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Open Services for Lifecycle Collaboration
Core Specification Version 2.0
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This Version
Latest Version
Authors
- Dave Johnson, Steve Speicher
Contributors
Table of Contents
License
This work is licensed under a
Creative Commons Attribution License.
Notation and Conventions
The key words "MUST", "MUST NOT", "REQUIRED, SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY" and "OPTIONAL" in this document are to be interpreted as described in
RFC-2119. This document is a mixture of normative and informative text. See the
the glossary below for definitions of these terms.
Overview
(this section is informative)
The Open Services for Lifecycle Collaboration (OSLC) initiative is creating a family of web services specifications for products, services and other tools that support all phases of the software and product lifecycle. The purpose of these specifications is to enable integration between products that support Application Life-cycle Management (ALM) and Product Life-cycle Management (PLM). Each part of the lifecycle or domain has its own group and specification, for example there are Change Management, Quality Management, Estimation & Measurement and more. Each of the domain specifications are built upon this core specification.
This OSLC Core Specification sets out the common features that every OSLC Service can be expected to support using terminology from the World Wide Web Consortium (W3C). New terminology that we introduce can be found in the glossary section below. This specification is mostly about OSLC Services, it specifies what OSLC Services MUST, SHOULD and MAY do. It also contains some required behaviors for OSLC clients and rules for OSLC domain specifications that extend this specification.
OSLC Services are accessible via a Service Provider Resource that describes the Services offered. Each Service can provide Creation Factories for resource creation, Query Capabilities for resource query and Delegated UI Dialogs to enable clients to create and select resources via a web UI. Query Capabilities and Creation Factories may offer Resource Shapes that describe the properties of resources managed by the service. This is illustrated in the diagram below. See the section below on Service Provider Resources for further discussion of these concepts.
Figure #1: OSLC Core Specification concepts and relationships
This specification establishes terminology and rules for defining resources in terms of the property names and value-types that are allowed and required. OSLC domain specifications are expected to use these rules and terminologies to describe their resources. See the OSLC Defined Resources section for more on this topic.
This specification also sets out rules for creating resource representations in RDF/XML, JSON, Atom and Turtle formats. OSLC domain specifications are expected to refer to these rules when specifying how their resources are to be represented. See the OSLC Defined Resource Representations section for the representation rules and examples of each format.
About the version number. We use the version number "2.0" even though there has never been an OSLC Core Version 1.0 specification. We do this because this OSLC Core specification was written after a series of version 1.0 domain specifications were finalized by OSLC workgroups. The version 2.0 domain specifications will all be based on this Core specification and
to avoid confusion this specification will also be known as Version 2.0.
About RDF. The resource and property-based data model used in OSLC resources is based on the Resource Description Framework (RDF) and OSLC requires RDF representations, but OSLC uses a small number of RDF concepts and does not require implementers to provide an RDF triple-store or a SPARQL query-engine.
Design considerations
The core philosophies of OSLC are to build on the powerful and scalable architecture of the World Wide Web and to do the simplest possible things that will work.
Build on the WWW. OSLC builds on the architecture of the WWW and follows the REST architectural pattern. This means that OSLC Services provide a uniform HTTP interface, OSLC URIs are stable and opaque and, in simple terms, OSLC works like the web.
Keep things simple. Doing the simplest things that will possibly work means a couple of different things in regard to OSLC. It means starting with simple and existing concepts. For example, we model everything as resources with property values and do not stray from that model. Keeping things simple also means building on established and well-known specifications, but also carefully limiting the number of other specifications that we reference. This simplicity is intended to enable loose coupling and to make life easier for everybody: OSLC domain work groups, OSLC Service implementers and OSLC client developers.
Accommodate different schemas. Because of the breadth of the OSLC domains, spanning lifecycle and platforms, OSLC has to work for systems with very different data schemas or no schemas at all. Flexibility is needed, but some OSLC Services must be able to offer information about resource properties so that clients can learn which are allowed and required for resource creation, query and reporting.
Accommodate different representations. Different client platforms might require or at least prefer different representations. For example, in the browser a JSON or Atom format representation might work best. OSLC Services will all support RDF/XML and may support other formats including JSON, Atom and Turtle.
Align with the W3C Linked Data initiative. Instead of defining a new data model, OSLC’s resource and property-value approach is based on industry standard Resource Description Framework (RDF) data model. This model allows OSLC to keep things simple, build on the WWW and accommodate different schemas.
Glossary of terms
This is a guide to some of the terminology used in this document. The following definitions are standard W3C concepts. OSLC uses these concepts without modification – their definitions are summarized here for the convenience of the reader. See
http://www.w3c.org.
- Resource: A network data object or service that can be identified by a URI. Resources may be available in multiple representations (e.g. multiple languages, data formats, size, resolutions) or vary in other ways. (reference: HTTP)
- Representation: An HTTP payload entity, included in an HTTP response, that is subject to content negotiation. There may exist multiple representations. associated with a particular HTTP response status. (reference: HTTP)
- URI: Uniform Resource Identifiers are simply formatted strings which identify--via name, location, or any other characteristic -- a resource (reference: URI Syntax)
Here are the OSLC specific terms used in this specification.
(these definitions are normative)
- OSLC Domain: an OSLC Domain is one ALM or PLM topic area such as Change Management, Requirements management or Automation. Each OSLC Domain will have its own OSLC specification that complies with this Core specification.
- OSLC Service: a set of capabilities that enable a web client to create, retrieve, update and delete resources managed by an ALM or PLM product or online service offering and associated with one OSLC Domain.
- OSLC Service Provider: a product or online service offering that provides an implementation of one or more OSLC Services, which may themselves implement different OSLC Domain specifications.
- OSLC Resource: a resource that is managed by an OSLC Service, may have properties and may link to other resources including those provided by other OSLC Services.
- OSLC Defined Resource: a resource that is defined by an OSLC specification, see OSLC Defined Resources below.
- OSLC Defined Properties: resource properties that are defined by an OSLC specification, defined by an OSLC Resource Shape or both.
- OSLC Resource Shape: defines the set of OSLC Properties expected in a resource for specific operations (i.e. creation, update or query) for each their value types, allowed values, cardinality and optionality. Examples of such operations include OSLC Creation Resource and Query Resource. Other examples might include applications that display data in tables.
- OSLC Creation Factory. A creation factory provides a URI used to create new resources via HTTP POST and may also provide Resource Shapes that describe the types of resources that may be created.
- OSLC Query Capability: A query capability provides a base URI for forming query resource URIs and, optionally, Resource Shapes that describe the property values that may be used in query expressions and returned in query results.
- OSLC Response Info Resource: An OSLC Defined Resource that provides information about a paged resource representation, e.g. the next page in a multi-page query result representation.
Here are some industry terms that we use in this specification:
- Application Lifecycle Management (ALM): ALM is the marriage of business management to software engineering made possible by tools that facilitate and integrate requirements management, architecture, coding, testing, tracking, and release management (http://en.wikipedia.org/wiki/Application_lifecycle_management).
- Product Lifecycle Management (PLM): In industry, product lifecycle management (PLM) is the process of managing the entire lifecycle of a product from its conception, through design and manufacture, to service and disposal (from http://en.wikipedia.org/wiki/Product_lifecycle_management).
And finally, we use the following two terms to describe portions of the OSLC Core specification:
- Normative. Normative sections of this document set forth requirements that must be met to establish conformance with the OSLC Core specification; or providing recommendations or optional courses of action. This is done using use words from RFC-2119 (e.g. MUST, SHOULD, MAY, etc.). For recommended or optional features, conformance is not dependent on the fact of implementation, but, if implemented, that implementation is as prescribed in this specification. Contrast with informative.
- Informative. Informative text provides background or explanation. Contrast with Normative. It should be clear which sentences and paragraphs are informative from the context and the absence of RFC-2119 keywords. Sections that are purely informative will be marked as informative. Informative text that might be mistaken for normative will also be marked.
OSLC Defined Resources
An OSLC Resource is a resource managed by an OSLC Service. An OSLC Resource is typically something like a Change Request, a Requirement or some other ALM or PLM artifact or record, but an OSLC Resource could also be a video or a presentation file. The resource’s storage medium is unconstrained by OSLC, e.g. it could be stored in a relational database, a flat-file on disk, a source code control system, or in any other way.
An OSLC Service can manage any type of resource; OSLC specifications only constrain an OSLC Service’s behavior with respect to resource types it manages that are defined by OSLC specifications (OSLC Defined Resources). OSLC Defined Resources may be specified in any OSLC specification, including this document. Resources are defined by the properties that are allowed and required in the resource.
OSLC Defined Resources
OSLC uses a simple model of resources with property values intended to be consistent with the Resource Description Framework (RDF) data model (reference: RDF Concepts). OSLC also builds upon the Extensible Markup Language (XML) namespace mechanism (reference: XML Namespaces).
When specifying a resource or a property, OSLC Specifications define its type as a URI which can be decomposed into a namespace URI and a name. We abbreviate type URIs as Prefixed Names (reference: Prefixed Names), which are represented in XML as QNames. The namespace used for resources defined in this specification is defined as follows:
- Namespace URI:
http://open-services.net/ns/core#
- Default Prefix:
oslc
When defining an OSLC Resource type, OSLC Specifications
MUST provide the following information:
- Name (String): name of the resource which MUST be valid as the Local Name part of a QName (reference: XML Namespaces).
- URI (URI): The URI of the resource definition. Per the rules of Prefixed Names, this URI is formed by appending the Name to the end of the Namespace URI in the specification that defines the resource. For example, the resource named Service (defined below) gets the Type URI of
http://open-services.net/ns/core#Service.
Once a resource type is defined, its allowed and required properties can be defined.
Regardless of any property definitions, providers and clients MAY impose implementation-specific limits on resources they accept. For example, they are not required to accept/create/store resources whose RDF triples contain objects with arbitrarily large literal values.
Defining OSLC Properties
OSLC Specifications
MAY provide a list of properties allowed and/or required for a particular domain and operation on an OSLC Defined Resource; if no operation is specified, then the list
applies to all operations governed by that specification. Specifications that provide a list of properties and constraints on them
SHOULD provide the following information for each property that they define.
- Name: name of the property which MUST be valid as the Local Name part of a QName (reference: XML Namespaces).
- URI: The URI that identifies the property. The URI is formed by appending the Name to the end of the Namespace URI associated with the property. For example, the resource named
oslc:ServiceProviderCatalog (defined below in the Service Providers Section) defines a property named domain with the URI of http://open-services.net/ns/core#domain
- Description: Description of the property.
- Occurs: value MUST be one of:
- Value-types: A property MAY allow multiple value-types and a value MUST satisfy one or more of them. Each value-type MUST be a URI that corresponds to one of the following:
- Literal value-types:
- Boolean: a boolean type as specified by XSD Boolean (
http://www.w3.org/2001/XMLSchema#boolean, reference: XSD Datatypes).
- DateTime: a Date and Time type as specified by XSD dateTime (
http://www.w3.org/2001/XMLSchema#dateTime, reference: XSD Datatypes).
- Decimal: a decimal number type as specified by XSD Decimal (
http://www.w3.org/2001/XMLSchema#decimal, reference: XSD Datatypes).
- Double: a double floating-point number type as specified by XSD Double (
http://www.w3.org/2001/XMLSchema#double, reference: XSD Datatypes).
- Float: a floating-point number type as specified by XSD Float (
http://www.w3.org/2001/XMLSchema#float, reference: XSD Datatypes).
- Integer: an integer number type as specified by XSD Integer (
http://www.w3.org/2001/XMLSchema#integer, reference: XSD Datatypes).
- String: a string type as specified by XSD String (
http://www.w3.org/2001/XMLSchema#string, reference: XSD Datatypes).
- XMLLiteral: a Literal XML value (
http://www.w3.org/1999/02/22-rdf-syntax-ns#XMLLiteral ).
- Resource value-types:
- Representation: for properties with a resource value-type, OSLC specifications should also specify how the resource will be represented. The options are
http://open-services.net/ns/core#Reference , http://open-services.net/ns/core#Inline or http://open-services.net/ns/core#Either .
- Range: for properties with a resource value-type, OSLC specifications should follow the best practices in Appendix C Guidance on Links and Relationships, which usually results in no restrictions on the range of possible resource types allowed, and an informative recommendation in the property description suggesting which resource types implementations should expect to find. This can be specified as a list of one or more resource types specified by URI reference; when no restrictions are required, use the string any. Clients SHOULD allow any resource type as the target of a link. Providers are strongly RECOMMENDED to behave reasonably for all resource types listed in a property’s description, and to degrade gracefully for others, as defined in Appendix C.
- Read-only: Boolean indication of whether or not clients are permitted to replace the property’s value after the resource has been created. Allowable values are: true, false, unspecified.
- True indicates that providers SHOULD NOT permit clients to change the property’s value after the resource has been created.
- False indicates that providers MAY permit clients to change the property’s value after the resource has been created.
- Unspecified indicates that the domain specification leaves the choice up to provider implementations.
In the rest of this document we will define OSLC resources as described above. The below section titled OSLC Defined Resource Representations defines how OSLC resources are to be represented in RDF/XML, JSON and other formats.
OSLC Services that wish to provide the information above in a machine-readable format
MAY use OSLC Resource Shapes, see
Appendix A: Common Properties and Resources for more information.
NOTE: we do not mention Internationalization of strings here because we expect standard HTTP content-negotiation and representation (e.g.
xml:lang) mechanisms to be used for such.
Unknown properties and content
For OSLC Defined Resources, clients
SHOULD assume that an OSLC Service will discard unknown property values. An OSLC Service
MAY discard property values that are not part of the resource definition or Resource Shape known by the server. If a client needs verification that the requested update was accepted it
SHOULD note the HTTP response header ETag value returned with the HTTP PUT, Immediately HTTP GET the resource back and compare the HTTP response header ETag value and contents with its expectations. The Service
SHOULD not return an error code for unrecognized content. A Service
MUST return an error code if recognized content is invalid.
The rule is different for clients. When doing an update, OSLC clients
MUST preserve any unknown property-values and other content in OSLC Defined Resources.
See following section on Resource Update.
Resource Operations
OSLC Services use HTTP for create, retrieve, update and delete operations on resources. OSLC Services
MUST comply with the HTTP specification (reference: HTTP).
Resource Creation
(this section is informative)
To create an OSLC Defined Resource, or any type of resource managed by an OSLC Service, an OSLC client HTTP POSTs a representation of that resource to a Creation URI. See the section on
Creation Factories for more information.
Resource Removal
(this section is informative)
To delete an OSLC Defined Resource, or any type of resource managed by a service, a client performs an HTTP DELETE on the resource's URI.
Resource Update
To update an OSLC Resource in an OSLC Service, a client fetches a representation of that resource via HTTP GET. The client updates the representation and then uses HTTP PUT to send the new representation to the resource's URI.
Recall from
OSLC Defined Resources: Unknown properties and content above that, when doing an update, OSLC clients must preserve any unknown property-values and other content in OSLC Defined Resources.
Because the update process involves first getting a resource, modifying it and then later putting it back to the server there is the possibility of a conflict, e.g. some other client may have have updated the resource since the GET. To mitigate this problem, OSLC Services
SHOULD use the HTTP
If-Match header:
- If the HTTP
If-Match header is missing OSLC Services SHOULD return HTTP Bad Request (400) status code to indicate that the header is required.
- If the HTTP
If-Match header is present OSLC Services MUST behave as described in the HTTP specification, returning an HTTP Precondition Failed (412) error to indicate that the header does not match.
- If the HTTP
If-Match header is present and it matches, but there is some other problem or conflict with the update then OSLC Services MAY return an HTTP Conflict (409) to indicate that problem.
Note that section
Error Responses below, we specify that when an error occurs and useful information can be provided to clients OSLC Services
SHOULD return error information in the body of the response.
Resource Paging
OSLC Services
MAY support a technique called Resource Paging to enable clients to retrieve resources one page at a time.
When a client requests a resource, the client can expect that the entire resource will be returned in the response, with all property values. This can be problematic because, in some cases, resources may be so large that a client might not want to retrieve the entire resource in one HTTP response.
One solution for response size-sensitive Clients is to check size before loading. Clients that do not wish to load large resources can use the HTTP HEAD method to determine the size of a resource and, according to the rules of HTTP the server's
SHOULD include an HTTP Content-Length header that indicates the size of the resource as the "decimal number of OCTETs." If the size is too large, a client can choose not to retrieve the resource.
Another solution is to use Resource Paging; here's how it works. To get a paged version of a resource, a client adds the "key=value" pair
oslc.paging=true to the query component of the resource URI and the server
MAY respond by returning a representation that contains partial information about the resource; only a subset of the resource's property values.
When a page is returned and it is
NOT the last page in the sequence, then it
SHOULD include an
oslc:ResponseInfo (defined below), which that contains a resource-valued property
oslc:nextPage that links to a resource that represents the next page of property-values. Because paging is unstable (see below), by the time a client follows an
oslc:nextPage link there may no longe be a next page, in this case the server
MAY respond with an HTTP 404 Page Not Found status code.
A client can also request paging by adding the "key=value" pair
oslc.pageSize to the query string component of the resource URI. By adding this, a client requests that the server respond with a specific number of property values. For example,
oslc.pageSize=20 indicates to the server that the client would like 20 values per page. OSLC Services
MAY ignore
oslc.pageSize.
When Resource Paging is used, the values of a multi-valued property
MAY be split across resource pages. Each property value
MUST be represented in its entirety and not split across multiple partial resource pages.
Provider response-size limitations
When a client requests a resource that an OSLC Service considers to be too large to return in one response and the client has not indicated that it desires paging (via oslc.paging or oslc.pageSize), the OSLC Service
MAY redirect the client to a representation that contains partial information about the resource, as follows:
- The OSLC Service receives an HTTP GET request for a resource that exceeds size limits and URL does not include
oslc.paging or an oslc.pageSize key/value pair.
- The OSLC Service returns an HTTP Status 302 redirect a URL that does include the key/values for paging, as follows:
- If the client did not indicate paging, the new redirect URL MUST include the
oslc.paging pair.
- If the client indicated a page size, then the redirect URL MUST include the
oslc.pageSize pair with a size value that is acceptable to the service.
- The client MAY choose to follow the redirect and receive a representation that contains partial information about the resource.
On receiving a resource representation, OSLC Clients
SHOULD check for the presence of an
oslc:nextPage value to determine if the representation contains partial information about the resource. If the value is present, then paging is in effect and the representation contains partial information about the resource.
Unstable Paging
Because HTTP is a stateless protocol and OSLC Services manage resources that can change frequently, OSLC clients
SHOULD assume that resources can change as they page through them using the
oslc:nextPage mechanism.
Stable Paging
Some OSLC Services might wish to guarantee stable paging, meaning that the chain of
oslc:nextPage links in a resource represent a snapshot in time and will not change as the client pages through them. OSLC specifications that require stable paging
SHOULD state this requirement and specify to which resources it applies.
Note that because stable paging implementations are based on server-side state, it is possible that such state will expire. Implementations
MAY use the HTTP response code 410 (Expired) to indicate to clients that the next-page link they requested has expired.
Response Information
Resource representations returned via Resource Paging
MUST include a resource of type
oslc:ResponseInfo, as defined in this section. A response info resource representation describes information about a paged HTTP response body in which it appears.
- Name:
ResponseInfo
- URI:
http://open-services.net/ns/core#ResponseInfo
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
dcterms:title |
zero-or-one |
True |
XML Literal |
n/a |
n/a |
Title of the response |
dcterms:description |
zero-or-one |
True |
XML Literal |
n/a |
n/a |
Description of response |
oslc:nextPage |
zero-or-one |
True |
Resource |
Reference |
any |
Link to next page of response |
oslc:totalCount |
zero-or-one |
True |
Integer |
n/a |
n/a |
This optional property indicates the total number of results across all pages, its value should be non-negative. In the context of a query resource, this value SHOULD be the total number of results, i.e. the number of resources that match the query. In the context of other resources, the value SHOULD be the total number of property values (i.e. RDF triples) of the resource. Unless Stable Paging is in effect, the total count MAY vary as a client retrieves subsequent pages. |
The subject resource URI of the
oslc:ResponseInfo resource representation will be the HTTP request URI, or URI from subsequent redirects. The response representation may also include properties from subject resources different from the one identified by the request URI.
Here's an example, using the OSLC Core RDF/XML representation guidance, that illustrates how the
oslc:ResponseInfo resource representation is included in addition to the blog entry resource representation.
Example: Resource Paging, partial response with response info resource representation
Example URI:
http://example.com/blogs/entry/1?oslc.paging=true&pageno=2
<rdf:RDF
xmlns:oslc_blog="http://open-services.net/ns/bogus/blogs#"
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:foaf="http://http://xmlns.com/foaf/0.1/"
xmlns:dcterms="http://purl.org/dc/terms/">
<oslc_blog:Entry
rdf:about="http://example.com/blogs/entry/1">
<!-- partial property values of of the blog entry -->
</oslc_blog:Entry>
<oslc:ResponseInfo rdf:about="http://example.com/blogs/entry/1?oslc.paging=true&pageno=2">
<oslc:nextPage rdf:resource="http://example.com/blogs/entry/1?oslc.paging=true&pageno=3" />
</oslc:ResponseInfo>
</rdf:RDF>
Refer to the OSLC Defined Resource Representation guidance for an explanation of how the response info resource may be represented in RDF/XML.
Selective Property Values
OSLC Services
MAY support a technique called Selective Properties to enable clients to retrieve only selected property values.
By adding the key=value pair
oslc.properties, specified below, to a resource URI, a client can request a new resource with a subset of the original resource's values. Here's how the selective properties values
oslc.properties and
oslc.prefix work.
oslc.properties
The
oslc.properties key=value pair lets you specify the set of properties to be included in the response. Both immediate and nested properties may be specified. A nested property is a property that belongs to the resource referenced by another property. Nested properties are enclosed in brace brackets, and this nesting may be done recursively, i.e. a nested property may contain other nested properties.
For example, suppose we have a bug report resource at the following URL:
http://example.com/bugs/4242
Suppose this bug resource has properties such as
dcterms:title,
dcterms:description, and
dcterms:creator, and that
dcterms:creator refers to a person resource that has properties such as
foaf:givenName and
foaf:familyName. Suppose you want a representation of the bug report that includes its
dcterms:title and the
foaf:givenName and
foaf:familyName of the person refered to by its
dcterms:creator. The following URL illustrates the use of the
oslc.properties query value to include those properties:
http://example.com/bugs/4242?oslc.properties=dcterms:title,dcterms:creator{foaf:givenName,foaf:familyName}
Syntax
The
oslc.properties pair is defined by the
oslc_properties term in the following BNF grammar:
oslc_properties ::= "oslc.properties=" properties
properties ::= property ("," property)*
property ::= identifier | wildcard | nested_prop
nested_prop ::= (identifier | wildcard) "{" properties "}"
wildcard ::= "*"
identifier ::= PrefixedName
PrefixedName ::= /* see "SPARQL Query Lanaguage for RDF", http://www.w3.org/TR/rdf-sparql-query/#rPrefixedName */
oslc.prefix
In our examples of
oslc.properties, property names include a URI prefix, i.e.
dcterms: or
foaf:. An OSLC Service
SHOULD predefine URI prefixes for its properties. Here we assume that OSLC has predefined the Dublin Core (
dcterms:) and Friend of a Friend (
foaf:) prefixes. However, OSLC resources
SHOULD also be open to new content, which means that new properties may not have predefined URI prefixes. We therefore need a way to define new URI prefixes in resource requests. The
oslc.prefix value lets you specify URI prefixes used in property names. For example, suppose the
foaf: prefix was not predefined. The following URL illustrates the use of the
oslc.prefix value to define it:
http://example.com/bugs/4242?oslc.prefix=foaf=<http://xmlns.com/foaf/0.1/>&oslc.properties=foaf:lastName,...
Syntax
The syntax of the
oslc.prefix is defined by the
oslc_prefix term in the following BNF grammar:
oslc_prefix ::= "oslc.prefix=" prefix_defs
prefix_defs ::= prefix_def ("," prefix_def)*
prefix_def ::= prefix "=" uri_ref_esc
prefix ::= PN_PREFIX
PN_PREFIX ::= /* see "SPARQL Query Lanaguage for RDF", http://www.w3.org/TR/rdf-sparql-query/#rPN_PREFIX */
uri_ref_esc ::= /* an angle bracket-delimited URI reference in which > and \ are \-escaped. */
Common Properties
OSLC domains specifications are strongly encouraged to use the common properties approved by the OSLC Core Workgroup (See
OSLC Core Spec Appendix A) rather than defining new properties.
Service Provider Resources
OSLC Services are accessible via a Service Provider Resource that describes each service, which domain specifications the service implements as well as the creation, query and delegated UI capabilities of each service.
Additionally, a provider may offer a Service Provider Catalog that lists related Service Providers.
Conceptual Model
The conceptual model of Service Provider Catalog and Service Provider resources is simple. They are both resources with property values. The values allowed and required in each type of resource are defined below.
The diagram below illustrates the Service Provider Catalog and Service Provider concepts and relationships. As you can see there are two Resources defined: Service Provider Catalog and Service Provider. There are also a set of Local In-Line Resources that are used inside the Resources to define namespaces, OAuth configurations, contributors as well as services and their capabilities.
Figure #2: Service Provider concepts and relationships
Next, we will formally define the Service Provider Catalog and Service Provider resources.
Resource: Service Provider Catalog
An OSLC implementation that offers one or more Service Provider resources (see below), MAY also provide Service Provider Catalog to enable OSLC clients to find Service Providers offered. These catalogs may contain other nested catalogs as well as service providers.
- Name:
ServiceProviderCatalog
- URI:
http://open-services.net/ns/core#ServiceProviderCatalog
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
dcterms:title |
zero-or-one |
True |
XMLLiteral |
n/a |
n/a |
Title of the service provider catalog |
dcterms:description |
zero-or-one |
True |
XMLLiteral |
n/a |
n/a |
Description of the service provider catalog |
dcterms:publisher |
zero-or-one |
True |
Local Resource |
Inline |
oslc:Publisher |
Describes the software product that provides the implementation. |
oslc:domain |
zero-or-many |
True |
Resource |
Reference |
n/a |
Namespace URI of the specification that is implemented by this service. In most cases this namespace URI will be for an OSLC domain, but other URIs MAY be used. |
oslc:serviceProvider |
zero-or-many |
True |
Resource |
Either |
oslc:ServiceProvider |
A service offered by the service provider. |
oslc:serviceProviderCatalog |
zero-or-many |
True |
Resource |
Either |
oslc:ServiceProviderCatalog |
Additional service provider catalog. |
oslc:oauthConfiguration |
zero-or-many |
True |
Local Resource |
Inline |
oslc:OAuthConfiguration |
Defines the three OAuth URIs required for a client to act as an OAuth consumer. |
Resource: Service Provider
A Service Provider describes a set of services offered by an OSLC implementation.
- Name:
ServiceProvider
- URI:
http://open-services.net/ns/core#ServiceProvider
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
dcterms:title |
zero-or-one |
True |
XMLLiteral |
n/a |
n/a |
Title of the service provider |
dcterms:description |
zero-or-one |
True |
XMLLiteral |
n/a |
n/a |
Description of the service provider |
dcterms:publisher |
zero-or-one |
True |
Local Resource |
Inline |
oslc:Publisher |
Describes the software product that provides the implementation. |
oslc:service |
one-or-many |
True |
Local Resource |
Inline |
oslc:Service |
Describes a service offered by the service provider. |
oslc:details |
zero-or-many |
True |
Resource |
Reference |
any |
A URL that may be used to retrieve a web page to determine additional details about the service provider. |
oslc:prefixDefinition |
zero-or-many |
True |
Local Resource |
Inline |
oslc:PrefixDefinition |
Defines a namespace prefix for use in JSON representations and in forming OSLC Query Syntax strings. |
oslc:oauthConfiguration |
zero-or-one |
True |
Local Resource |
Inline |
oslc:OAuthConfiguration |
Defines the three OAuth URIs required for a client to act as an OAuth consumer. |
Resource: Service
A Service describes the specific services offered by an implementation of an OSLC specification.
- Name:
Service
- URI:
http://open-services.net/ns/core#Service
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
oslc:domain |
exactly-one |
True |
Resource |
Reference |
n/a |
Namespace URI of the specification that is implemented by this service. In most cases this namespace URI will be for an OSLC domain, but other URIs MAY be used. |
oslc:creationFactory |
zero-or-many |
True |
Local Resource |
n/a |
oslc:CreationFactory |
Enables clients to create new resources |
oslc:queryCapability |
zero-or-many |
True |
Local Resource |
n/a |
oslc:QueryCapability |
Enables clients query across a collection of resources |
oslc:selectionDialog |
zero-or-many |
True |
Local Resource |
n/a |
oslc:Dialog |
Enables clients to select a resource via UI |
oslc:creationDialog |
zero-or-many |
True |
Local Resource |
n/a |
oslc:Dialog |
Enables clients to create a resource via UI |
Resource: Creation Factory
A Creation Factory describes a creation factory, capable of creating new resources via HTTP POST.
- Name:
CreationFactory
- URI:
http://open-services.net/ns/core#CreationFactory
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
dcterms:title |
exactly-one |
True |
XMLLiteral |
n/a |
n/a |
Title string that could be used for display |
oslc:label |
zero-or-one |
True |
String |
n/a |
n/a |
Very short label for use in menu items |
oslc:creation |
exactly-one |
True |
Resource |
Reference |
n/a |
To create a new resource via the factory, post it to this URI |
oslc:resourceShape |
zero-or-many |
True |
Resource |
Reference |
oslc:ResourceShape |
A Creation Factory MAY provide Resource Shapes that describe shapes of resources that may be created. |
oslc:resourceType |
zero-or-many |
True |
Resource |
Reference |
n/a |
The expected resource type URI of the resource that will be created using this creation factory. These would be the URIs found in the result resource's rdf:type property. |
oslc:usage |
zero-or-many |
True |
Resource |
Resource |
n/a |
An identifier URI for the domain specified usage of this creation factory. If a service provides multiple creation factories, it may designate the primary or default one that should be used with a property value of http://open-services.net/ns/core#default |
Resource: Query Capability
A Query Capability describes a query capability, capable of querying resources via HTTP GET or POST.
- Name:
QueryCapability
- URI:
http://open-services.net/ns/core#QueryCapability
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
dcterms:title |
exactly-one |
True |
XMLLiteral |
n/a |
n/a |
Title string that could be used for display |
oslc:label |
zero-or-one |
True |
String |
n/a |
n/a |
Very short label for use in menu items |
oslc:queryBase |
exactly-one |
True |
Resource |
Reference |
n/a |
The base URI to use for queries. Queries are invoked via HTTP GET on a query URI formed by appending a key=value pair to the base URI, as described in Query Capabilities section. |
oslc:resourceShape |
zero-or-one |
True |
Resource |
Reference |
n/a |
The Query Capability SHOULD provide a Resource Shape that describes the query base URI. |
oslc:resourceType |
zero-or-many |
True |
Resource |
Reference |
n/a |
The expected resource type URI that will be returned with this query capability. These would be the URIs found in the result resource's rdf:type property. |
oslc:usage |
zero-or-many |
True |
Resource |
Reference |
n/a |
An identifier URI for the domain specified usage of this query capability. If a service provides multiple query capabilities, it may designate the primary or default one that should be used with a property value of http://open-services/ns/core#default |
Resource: Dialog
A Dialog describes a delegated user interface (UI) which can be used to allow a user to interactively create a new resource or pick a resource.
- Name:
Dialog
- URI:
http://open-services.net/ns/core#Dialog
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
dcterms:title |
exactly-one |
True |
XMLLiteral |
n/a |
n/a |
Title string that could be used for display |
oslc:label |
zero-or-one |
True |
String |
n/a |
n/a |
Very short label for use in menu items |
oslc:dialog |
exactly-one |
True |
Resource |
Reference |
n/a |
The URI of the dialog |
oslc:hintWidth |
zero-or-one |
True |
String |
n/a |
n/a |
Values MUST be expressed in relative length units as defined in the W3C Cascading Style Sheets Specification (CSS 2.1) Em and ex units are interpreted relative to the default system font (at 100% size). |
oslc:hintHeight |
zero-or-one |
True |
String |
n/a |
n/a |
Values MUST be expressed in relative length units as defined in the W3C Cascading Style Sheets Specification (CSS 2.1) Em and ex units are interpreted relative to the default system font (at 100% size). |
oslc:resourceType |
zero-or-many |
True |
Resource |
Reference |
n/a |
The expected resource type URI for the resources that will be returned when using this dialog. These would be the URIs found in the result resource's rdf:type property. |
oslc:usage |
zero-or-many |
True |
Resource |
Reference |
n/a |
An identifier URI for the domain specified usage of this dialog. If a service provides multiple selection or creation dialogs, it may designate the primary or default one that should be used with a property value of http://open-services/ns/core#default |
Resource: Publisher
A Publisher identifies and describes the software product that provides the OSLC implementation.
- Name:
Publisher
- URI:
http://open-services.net/ns/core#Publisher
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
dcterms:title |
exactly-one |
True |
XMLLiteral |
n/a |
n/a |
Title string that could be used for display |
oslc:label |
zero-or-one |
True |
String |
n/a |
n/a |
Very short label for use in menu items |
dcterms:identifier |
exactly-one |
unspecified |
String |
n/a |
n/a |
A URN that uniquely identifies the implementation |
oslc:icon |
zero-or-one |
True |
Resource |
reference |
n/a |
URL to an icon file that represents the provider. This icon should be a favicon format and 16x16 pixels in size |
Resource: Prefix Definition
Service Providers
MUST provide a Prefix Definition for each prefix supported by the service. Each Prefix Definition defines a namespace prefix that clients
MAY use in forming OSLC Query Syntax strings.
- Name:
PrefixDefinition
- URI:
http://open-services.net/ns/core#PrefixDefinition
Resource: OAuth Configuration
Service Providers that support OAuth Authentication
SHOULD provide a way for clients to automatically discover the three OAuth URIs necessary to act as an OAuth Consumer.
- Name:
OAuthConfiguration
- URI:
http://open-services.net/ns/core#OAuthConfiguration
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
oslc:oauthRequestTokenURI |
exactly-one |
True |
Resource |
Reference |
n/a |
URI for obtaining OAuth request token |
oslc:authorizationURI |
exactly-one |
True |
Resource |
Reference |
n/a |
URI for obtaining OAuth authorization |
oslc:oauthAccessTokenURI |
exactly-one |
True |
Resource |
Reference |
n/a |
URI for obtaining OAuth access token |
The next sections cover the Creation Factory and Query Capability in more detail.
Creation Factories
An OSLC Service can provide one or more creation factory to enable the creation of new resources. A creation factory provides a Creation URI used to create new resources via HTTP POST and may also provide Resource Shapes that describe the types of resources that may be created. To create a new OSLC Resource, an OSLC client POSTs a representation of that resource to a Creation Factory's Creation URI.
- An HTTP POST of content to a Creation URI SHOULD result in the creation of a new resource or an explanation of why creation did not occur via the appropriate HTTP status code.
- The response to a successful HTTP POST of content to a Creation URI SHOULD include a HTTP Location header that specifies the URI of the newly created resource.
Creating an OSLC Defined Resource
To create an OSLC Defined Resource, an OSLC Client first forms an representation of that resource including the desired and required property values. A client can learn what properties are allowed in a new OSLC Defined Resource via the OSLC specification that defines or, in some cases via a Resource Shape resource. Next the client uses HTTP POST to post that representation to a Creation URI.
- The response to a successful HTTP POST of a representation to a Creation Resource URI MAY include a representation of the newly created resource.
- The resource returned MAY contain changes to properties made by the server or new properties added by the server.
Query Capabilities
An OSLC Service may provide one or more Query Capabilities to enable query of resources. A Query Capability provides a base URI for forming Query Resource URIs and
MAY provide Resource Shapes that describe the property values that may be expected in the resources that are queryable via the query capability. Thus, Query Capabilities provide a way to discover the resources managed by an OSLC Service.
In a Query Capability, the base URI, as defined by the
oslc:queryBase property, is itself a resource managed by the service and it acts as the starting subject resource for the queries based on it. Since the list may contains hundreds of thousands of members, queries are used to filter the list for members that satisfy certain conditions, e.g. the bugs that have high priority and were created this week.
Conceptual Model
To perform a query an OSLC client first creates a URI by starting with a Query Capability's base URI as a base and adding a URI Query String to express the query criteria. The OSLC client then uses HTTP GET to request a Query Resource representation of the query results. The Query Resource representation will contain property values about the query and a collection of resources that match the query criteria.
HTTP GET Queries
To perform an HTTP GET query, an OSLC client starts with the base URI as defined by the
oslc:queryBase property of a Query Capability, and appends to it query parameters in a syntax supported by the service. The resulting URI is the query URI. The OSLC client sends an HTTP GET request to the query URI, optionally specifying the preferred content media type for the query response in the HTTP Accept header. OSLC Services
MUST support query responses in RDF/XML format (media type
application/rdf+xml) and
MAY support other formats. OSLC Services
SHOULD support the Query Syntax defined in this specification, but
MAY support other syntaxes.
Query Syntax
A query URI can be formed by adding a query string to the end of the Query Capability's base URI (or by sending the query string in the request body when using HTTP POST). The syntax used to express the query criteria in that string is specified by each OSLC domain specification.
The
OSLC Core Spec Query Specification document defines a standard set of OSLC query parameters that other OSLC domain specifications
MAY use to query resources.
Query Specification errors
If there is an error in the specification of the query, whether the query is specified by key=value pairs in the HTTP GET URL or key=value pairs in the body of an HTTP POST, then the provider
MUST respond with an error. The error response should be an HTTP 400 Bad Request error and an explanation of the error in the OSLC Error Response format (see Error Responses below).
Delegated User Interface Dialogs
OSLC specifications target specific integration scenarios. In some cases, allowing one product to delegate to a user interface defined in another product is a more effective way to support a use case than an HTTP interface that can only be accessed programmatically. There are two cases where this is especially true:
- Resource creation: when a user of a web application needs to create a new resource in an OSLC Service Provider. In this case the web application asks the service provider to provide a UI for resource creation and the provider notifies the application when the creation has been completed or canceled by the user.
- Resource selection: when a user of a web application and needs to pick a resource managed by a OSLC Service Provider. In this case the web application asks the service provider to provide a UI for resource selection and the provider notifies the application when a resource or resources has been selected or if the selection was canceled.
To support these two cases, below we define OSLC Delegated User Interface (UI) Dialogs. Delegated UI Dialogs are a technique where one provider can embed a creation or selection UI into another using a combination of an HTML <iframe> and JavaScript code. The diagram below illustrates how delegated UI dialogs work in a scenario where Provider A wants to allow a user to select or create a resource managed by Provider B.
Figure #3: Delegated UI Dialog interactions
Next, the details of the Delegated UI Dialog protocol.
Terminology
The following terms are used in discussions of Delegated UI Dialogs:
- UI Consumer - a web application that is embedding a Delegated UI Dialog from an OSLC Service Provider. This consumer could be a web page, with the Delegated UI Dialog loaded into an iframe or a native application, e.g. an IDE like Eclipse, that is embedding a web browser component.
- UI Provider - an OSLC Service provider that offers one or more Delegated UI Dialogs. These dialogs will be specified in the provider's Service Provider resource.
The next sections explain how Delegated UI Dialogs work.
Post Message and Window Name protocols
To support the widest range of web browsers, we define two different protocols for communicating the information about the user's action from the UI Provider and back to the UI Consumer. These are the Post Message and Window Name protocols described below.
In both the Post Message and Window Name protocols, the way that a UI Consumer includes a Delegated UI Dialog in an HTML page is to create an
iframe and specify the
src as the URI of the Delegated UI Dialog to be included. The UI Consumer indicates the protocol to be used by appending one of the two fragment identifiers below to the URI:
-
#oslc-core-postMessage-1.0 - Indicates that the Post Message protocol is to be used
-
#oslc-core-windowName-1.0 - Indicates that the Window Name protocol is to be used
The JavaScript code example below shows now a UI Provider can determine which protocol is in use:
if (window.location.hash == '#oslc-core-windowName-1.0') {
// Window Name protocol in use
} else if (window.location.hash == '#oslc-core-postMessage-1.0') {
// Post Message protocol in use
}
iframe Creation Considerations
Regardless of the protocol in effect, it is recommended that UI Consumers follow the below iframe creation guidelines to provide a more seamless user experience:
- Embed the
iframe within a div element, with height and width set based on the relative length values specified in the Service Resource that declares the Delegated UI Dialog.
- Set the
iframe border size to '0'
- Set the
iframe scrolling to 'auto'
Next, the details for each of the two protocols.
Post Message Protocol
The Post Message protocol relies on the HTML5 function
window.postMessage() (reference: HTML5), available in the latest or pending releases of most browsers. UI Consumers must anticipate other, unrelated uses of postMessage(), and should ignore messages not conforming to this protocol.
Typically, the embedded page will be loaded in a window inside another window, such as a iframe inside some surrounding webpage. In such cases,
postMessage() must be called on that parent window. But in a native application, an outer page is not needed and the embedded page may be shown directly in the browser's "root" window. When the embedded page has no parent window, it must call
postMessage() on its own window.
Here are the responsibilities of the UI Consumer and UI Provider in Post Message protocol.
The UI Consumer's responsibilities
- Include the Delegated UI Dialog via iframe (i.e setting iframe src to the URI of the Delegated UI Dialog) or via an embedded browser. Append the fragment identifier #oslc-core-postMessage-1.0 to the URL to indicate that Post Message is the desired protocol.
- Add a 'message' listener to the outer window to receive messages from the Delegated UI Dialog.
- Listen for window 'message' events, ignoring events from other sources or not prefixed with "oslc-response:"
- When message from Delegated UI Dialog indicates user completed action, free resources and handle action.
The UI Provider's responsibilities
- Provide Delegated UI Dialog, an HTML page that provides a user interface for resource creation or selection.
- Allow the user to perform resource creation or selection.
- Once the user has created, selected or canceled, send notification using
postMessage() to the page's parent window, passed in event.data string, that is prefixed with "oslc-response:" See below for the two possible response formats, one for resource selection and one for creation.
- If the page is not parented, then the message is posted to the page's own window. The page must ignore this message to itself.
The below JavaScript code example shows how a UI Provider page would send a response using
postMessage() and taking into account the fact that some pages are not parented.
function respondWithPostMessage(/*string*/ response) {
(window.parent | window).postMessage("oslc-response:" + response, "*");
}
Now, the Window Name protocol.
Window Name Protocol
The Window Name protocol uses the HTML DOM
window.name property to communicate the response (reference: Window Object) from the UI Provider to the UI Consumer. This special property of window maintains its value even as the window navigates to a different origin, but the ifame's
window.name can only be read when the accessing window shares the same origin. For this to happen, when the embedded page is finished it must set the
window.name and also change the
window.location to a page with the same origin as the outer frame. This not only allows the UI Consumer to access the result, but also fires an event telling the UI Consumer when to do so. This return location is passed to the embedded page using the
window.name property.
Here are the responsibilities of the UI Consumer and UI Provider in Window Name protocol.
The UI Consumer's responsibilities
- Include the Delegated UI Dialog via iframe (i.e setting iframe src to the URI of the Delegated UI Dialog) or via an embedded browser. Append the fragment identifier #oslc-core-windowName-1.0 to the URL to indicate that Window Name is the desired protocol.
- On the iframe, set the frame's
window.name to indicate the Return URL.
- On the iframe, Listen for 'onload' events
- When an 'onload' event occures an the frame's location is equal to the Return URL then read the response from the window.name.
The following Javascript code illustrates the protocol. The code for the
destroyFrame(),
handleMessage() and
displayFrame() methods are not provided in this example, but should be obvious to a JavaScript developer. The UI Consumer must provide these methods.
var pickerURL = ... // URL of Provider's Delegated UI Dialog
var returnURL = ... // Consumer's Return URL
var frame = document.createElement('iframe');
function windowNameProtocol() {
// Step #1: create iframe with fragment to indicate protocol
// Step #2: set the iframe's window.name to indicate the Return URL
if (ie > 0) {
frame = document.createElement('<iframe name=\'' + returnURL + '\'>');
} else {
frame = document.createElement('iframe');
frame.name = returnURL;
}
frame.src = pickerURL + '#oslc-core-windowName-1.0';
frame.width = 450;
frame.height = 300;
displayFrame(frame);
// Step #3: listen for onload events on the iframe
var ie = window.navigator.userAgent.indexOf("MSIE");
if (ie > 0) {
frame.attachEvent("onLoad", onFrameLoaded);
} else {
frame.onload = onFrameLoaded;
}
}
function onFrameLoaded() {
try { // May throw an exception if the frame's location is still a different origin
// Step #4: when frame's location is equal to the Return URL
// then read response and return.
if (frame.contentWindow.location == returnURL) {
var message = frame.contentWindow.name;
destroyFrame(frame);
handleMessage(message);
}
} catch (e) {
// ignore: access exception when trying to access window name
}
}
The UI Provider's responsibilities
As soon as the embedded page has loaded, perform the following:
- Provide Delegated UI Dialog, an HTML page that provides a user interface for resource creation or selection.
- Read the Return URL from the window.name variable
- Allow user to perform resource creation or selection.
- Once user has created, selected or canceled, communicate the user's response by setting the window.name variable to the response. See below for the two possible response formats, one for resource selection and one for creation.
- Indicate that user has responded by setting the window.location to the Return URL specified by the UI Consumer.
The JavaScript example below shows a UI Provider notifying its UI Consumer after a user has responded.
function respondWithWindowName(/*string*/ response) {
// Step #2: read the return URL
var returnURL = window.name;
// Step #4: send the response via the window.name variable
window.name = response;
// Step #5: indicate that user has responded
window.location = returnURL;
}
Resource Selection
Resource Selection can be used when a UI Consumer wants to allow a user to pick a resource that is managed by an OSLC Service. Using either the Post Message or Window Name protocols defined above, the UI Consumer uses an iframe to embed a selection dialog that is provided by the service, then awaits notification that the user has selected a resource.
To enable Resource Selection, an OSLC Service
MUST provide in its Service Resource a value for the
oslc:selectionDialog property. The property value will include a
oslc:dialogURI property that indicates the URI of the selection dialog.
Regardless of how the response from the UI Provider is conveyed to the UI Consumer, the response
SHOULD be formatted as follows:
- Name:
results
- URI:
http://open-services.net/ns/core#results
An empty array indicates that the resource selector has been canceled
An example Resource Selection response:
{
"oslc:results" : [{
"oslc:label": "Bug 123: Server crash",
"rdf:resource": "http://example.com/bug123"
}, {
"oslc:label": "Bug 456: Client hangs on startup",
"rdf:resource": "http://example.com/bug456"
}
]
}
Resource Creation
Resource Creation can be used when a UI Consumer wants to allow a user to create a new resource that is managed by an OSLC Service. Using either the Post Message or Window Name protocols defined above, the UI Consumer uses an iframe to embed a creation dialog that is provided by the service, then awaits notification that the user has created a resource.
To enable Resource Creation, an OSLC Service
MUST provide in its Service Resource a value for the
oslc:creationDialog property. The property value will include a
oslc:dialogURI property that indicates the URI of the creation dialog.
Regardless of how the response from the UI Provider is conveyed to the UI Consumer, the response
SHOULD be formatted as defined by
oslc:results
Example:
{
"oslc:results" : [ {
"oslc:label": "Bug 123: Server crash",
"rdf:resource": "http://example.com/bug123"
}, {
"oslc:label": "Bug 456: Client hangs on startup",
"rdf:resource": "http://example.com/bug456"
}
]
}
Prefilling Creation Dialogs
Service providers
MAY support receiving a POST request whose content body is a resource definition to the Creation Dialog URI to retrieve a URI that represents the embedded page to be used. Service providers
MUST respond with a response status of 201 (Created) with the response header
Location whose value is the URI to request the newly created form. After some elapsed time, service providers
MAY respond with a 404 (Not Found), 410 (Gone) or 3xx (Redirect) to an HTTP GET request for these URIs.
Dialog Resizing
Delegated UI dialogs receive their initial size (dimensions) based on the
oslc:hintWidth and
oslc:hintHeight properties described in
oslc:Dialog resource description. There are cases where UI Provider recognizes that the initial size of a Delegated UI dialog is not sufficient and needs a way to ask the UI Consumer to resize the dialog. In this section we specify a mechanism that enables dialog resizing, but only when Post Message Protocol is used.
Consumers
MAY honor a dialog's ability to dynamically resize. Those that do (a)
MUST use Post Message Protocol, (b)
MUST use the
oslc:resize value instead of any static width or height, and and (c)
MUST register a handler to receive dialog resize messages sent by the dialog Provider and adjust the size of the dialog accordingly.
Since a dialog is allowed to resize itself any number of times, the Consumer
MUST keep a handler registered and react appropriately each time it received a dialog resize message from that dialog.
UI Providers
SHOULD NOT request sizes larger than 95% of the current
viewport, to avoid covering the entire viewport with the dialog.
Here are the responsibilities of the UI Consumer and UI Provider in dialog resizing.
The UI Consumer's responsibilities
- Include the Delegated UI Dialog via iframe (i.e setting iframe src to the URI of the Delegated UI Dialog) or via an embedded browser.
- Add a 'message' listener to the outer window to receive messages from the Delegated UI Dialog.
- Listen for window 'message' events, ignoring events from other sources or not prefixed with "oslc-resize:". Multiple resize 'message' events may be sent while the dialog is visible.
- When message from Delegated UI Dialog indicates user completed action, free resources and handle action.
The UI Provider's responsibilities
- Provide Delegated UI Dialog, an HTML page that provides a user interface for resource creation or selection.
- Allow the user to perform resource creation or selection.
- Once the Provider needs to resize the dialog, send notification using
postMessage() to the page's parent window, passed in event.data string, that is prefixed with "oslc-resize:". Multiple resize messages may be sent. See below for the response format.
- If the page is not parented, then the message is posted to the page's own window. The page must ignore this message to itself.
The below JavaScript code example shows how a UI Provider page would send a response using
postMessage() and taking into account the fact that some pages are not parented.
function respondWithPostMessage(/*string*/ resize_response) {
(window.parent | window).postMessage("oslc-resize:" + resize_response, "*");
}
Regardless of how the response from the UI Provider is conveyed to the UI Consumer, the response
SHOULD be formatted as follows:
An example Dialog Resize response with new height of '600px' and a width of '400px':
{
"oslc:hintHeight" : "600px",
"oslc:hintWidth" : "400px"
}
That brings us to the end of the Delegated UI section. Next up, another UI related topic.
User Interface Previews
OSLC providers
MAY support a technique known as User Interface (UI) Preview, that can be used to show a user in-context information when displaying a link to a resource, and to show more information when the user's mouse lingers over the link.
OSLC providers which offer UI Preview
MUST do so in accordance with the
OSLC Core UI Preview Specification.
Authentication
OSLC Services use standard web protocols for authentication. OSLC Services can use HTTP Basic Authentication, OAuth or both.
HTTP Basic Authentication
OSLC Services
MAY protect resources with HTTP Basic Authentication. OSLC Services that use HTTP Basic Authentication
SHOULD do so only via SSL.
OAuth Authentication
OSLC Services
MAY protect resources with OAuth Authentication.
Form Based Authentication
OSLC Services
MAY use other authentication mechanisms, including those common described as Form Based Authentication. OSLC Services that choose to use other authentication mechanisms are responsible for specifying how those mechanisms work.
Error Responses
OSLC Services the standard mechanisms of HTTP to report status and error codes to clients. When an error occurs and useful information can be provided to clients OSLC Services
SHOULD return error information in the body of the response.
OSLC Services
SHOULD use the Error resource defined below as the basis for forming error responses. OSLC Services
SHOULD return an Error resource using the same representation requested by the client via the HTTP Accept header.
Conceptual Model
The following OSLC Defined Resource can be used as the basis for forming an error response.
Resource: Error
- Name:
Error
- URI:
http://open-services.net/ns/core#Error
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
oslc:statusCode |
exactly-one |
True |
String |
n/a |
n/a |
The HTTP status code reported with the error. |
oslc:message |
exactly-one |
True |
String |
n/a |
n/a |
An informative message describing the error that occurred. |
oslc:extendedError |
zero-or-one |
True |
Either |
Either |
oslc:ExtendedError |
Extended error information |
Resource: Extended Error
- Name:
ExtendedError
- URI:
http://open-services.net/ns/core#ExtendedError
| Prefixed Name |
Occurs |
Read-only |
Value-type |
Represen-tation |
Range |
Description |
oslc:moreInfo |
zero-or-one |
True |
Resource |
Reference |
Any |
A resource giving more information on the error SHOULD be of an HTML content-type. |
oslc:rel |
zero-or-one |
True |
String |
n/a |
n/a |
If present and set to 'alternate' then indicates that work-around is provided, behavior for other values is undefined. |
oslc:hintWidth |
zero-or-one |
True |
String |
n/a |
n/a |
Values MUST be expressed in relative length units as defined in the W3C Cascading Style Sheets Specification (CSS 2.1) Em and ex units are interpreted relative to the default system font (at 100% size). |
oslc:hintHeight |
zero-or-one |
True |
String |
n/a |
n/a |
Values MUST be expressed in relative length units as defined in the W3C Cascading Style Sheets Specification (CSS 2.1) Em and ex units are interpreted relative to the default system font (at 100% size). |
Specification Versioning
One of the goals of the OSLC initiative is to mitigate or eliminate the need for lock-step version upgrades, where clients or services target one version of a specification and break when new versions are introduced -- requiring all services to be upgraded simultaneously.
In this section we specify a version header that will enable old "Version 1" OSLC clients to continue to work and share the same resource URIs as used by clients that specifically target the Core. And we establish rules that will enable clients to continue to work as new versions of specifications are introduced.
Supporting pre-Core clients
We anticipate that the OSLC Core and domain specifications will each be versioned independently and each version will be assigned a version number, but we would like to avoid exposing version numbers in OSLC implementations. There is one use case that requires version information to be exposed. We must ensure that old OSLC "Version 1" clients continue to work.
To enable OSLC Service specifications to evolve without breaking existing clients, we introduce an HTTP Header,
OSLC-Core-Version set to the Core specification version number
"2.0". We expect clients that target the Core to send this HTTP header.
- If the
OSLC-Core-Version header is present and set to a version that the service can support, then the service MUST return a representation that is complies with the specified version.
- If the
OSLC-Core-Version header is present and indicates a specification version that the service cannot support, the service SHOULD respond with what it determines is the most compatible version that it can return.
- If the
OSLC-Core-Version header is not present then the OSLC Service SHOULD respond by returning a resource that conforms to the earliest or most compatible (as determined by the implementation) specification version's representation. Services that never offered an OSLC Version 1 interface can ignore this restriction.
- When returning an OSLC Defined Resource, OSLC Services MUST return the
OSLC-Core-Version header set to the Core specification with which the representation complies.
Rules for new versions of OSLC specifications
When specifying a new version of an OSLC specification the rule is this:
A new version of an OSLC specification is not allowed to introduce changes that will break old clients.
Here are some guidelines for OSLC workgroups defining new specifications or upgrades to existing ones:
- If you believe that you need a property but cannot agree on the value-type, then this is a strong indication that you should not attempt to standardize on the property. Once you decide on a value-type you are stuck with it forever. Wait until you have the scenarios or implementation experience needed to agree on type.
- When introducing a new capability in a new version of a specification, e.g. a creation factory, query capability or delegated UI dialog; one that works differently than those specified in the Core spec or older versions of your own specification, you should create a new resource type to represent the service. This will enable old clients to continue to work against old services and new clients to work with your new capabilities.
- When defining resources, do not remove, change the meaning or the value-type of any properties that you defined in earlier versions of the specification. You can add new properties but not change those that already exist.
- It is possible to relax restrictions on clients, because relaxing restrictions should not break clients. But it is not possible to relax restrictions on services, because clients expect to find the required fields and if they are missing, clients will break.
- Before defining a new property within your OSLC domain's namespace consult the list of common properties in OSLC Core Spec Appendix A to see if using a common property would be more appropriate.
Migrating to the Core Specification
Most of the first OSLC specifications were developed before this Core specification existed and do not implement versioning as described above and so must use some other mechanism to migrate to the OSLC Core v1.0 specification.
OSLC implementations that wish to continue to support old pre-Core OSLC or OSLC v1.0 specifications can do so by keeping the old implementation in place and adding the new OSLC Core v1 implementation with different service provider, query capability and creation factory URIs.
OSLC Defined Resource Representations
This section specifies what resource representations are required for OSLC resources, some requirements for providing representations and some rational for the requirement that OSLC Services provide RDF/XML representations.
OSLC resource representations come in many forms and are subject to standard HTTP mechanisms for content negotiation.
OSLC domain specifications (1)
SHOULD require the representations needed for the specific scenarios that they are addressing and (2)
SHOULD recognize that different representations are appropriate for different purposes. For example, browser oriented scenarios might be best addressed by JSON or Atom format representations. For these reasons, OSLC Services
MAY provide and accept standard or emerging standard formats such as XML, JSON, HTML, Turtle and the Atom Syndication Format.
OSLC domain specifications are also expected to follow common practices and conventions that are in concert with existing industry standards and offer consistency across domains. All of the OSLC specifications are built upon the standard RDF data model, allowing OSLC to align with the
W3C? 's Linked Data initiative. In addition, all OSLC specifications have adopted the convention to illustrate RDF/XML representations and will typically require RDF/XML representations to enable consistency across OSLC implementations. For those reasons, OSLC Services
SHOULD provide and accept RDF/XML representations for each OSLC resource.
Though the OSLC Core workgroup does provide guidance on how to form RDF/XML representations using a subset of RDF/XML (reference:
Appendix B - Representation Guidance and Examples), OSLC clients
SHOULD NOT assume any specific form of RDF/XML. It is
RECOMMENDED that OSLC Services also provide an HTML representation for each resource.
Use standard content-types
Note that existing standard content-types are used, e.g.
application/rdf+xml and
application/json, in this document and no new content-types are introduced (except for the one introduced in the
UI Preview specification). Those writing OSLC specifications are strongly encouraged to follow this pattern -- use standard and existing content-types and avoid inventing new content-types for existing formats.
In past OSLC specifications we defined a specific RDF/XML format for each resource defined and gave each its own content-type. This implied to consumers that each resource had a different format when in reality they were all standard RDF/XML. Using different content-types makes it more difficult to write generic tools, crawlers and other services that work across all data.
Order of property values insignificant
This specification defines how OSLC property values are to be represented in a variety of formats. Except in the case of a sorted Query Response, the ordering of property values is insignificant. OSLC clients and service providers
MUST not place any significance on the ordering of property values in representations.
Use Absolute URIs
OSLC representations
MUST use absolute URIs in all cases except XML representations, where the
xml:base attribute may be used to allow relative URIs to be resolved to absolute form (reference: XML Base).
Before a resource representation that uses xml:base is posted to an OSLC Service for creation, it may include relative URIs that cannot be resolved until the OSLC Service has received, created and assigned a URI to the new resource.
Appendix A: Common Properties and Resources
See separate page
OSLC Core Spec Appendix A
Appendix B: Representation Guidance and Examples
See separate page
OSLC Core Spec Appendix B
Appendix C: Guidance on Links and Relationships
See separate page
OSLC Core Spec Appendix C
Appendix D: References
These are the specifications referenced by the OSLC Core Specification.
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