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Open Services for Lifecycle Collaboration
Partial Update Specification Version 2.0

Status: Working Draft

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Table of Contents

Contents

  • Appendix A: Notices and References

    • License

    Creative Commons Attribution 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 RFC2119. Domain name examples use RFC2606.

    Introduction

    There are many motivating cases for supporting a writable Web, existing approaches have focused heavily on the usage of HTTP PUT as the method for updating resources. As experience has shown, this method for updating resources comes with some significant limitations and performance costs. This has motivated the creation of the IETF Proposed Standard titled “PATCH Method for HTTP” RFC5789 which introduces a new HTTP verb called PATCH. RFC5789 defines the semantics of the new HTTP verb PATCH but does not endorse a patch representation or a patch model for Linked Data resources.

    Motivated by our use cases and requirements, partial update can be simple. Given a resource URL, triples can be added or removed.

    This document recommends to use HTTP PATCH to implement partial update, provides a patch model based on a subset of SPARQL Update SPARQL-Update, includes a recommended PATCH document formats based on existing RDF formats and provides examples of how this approach works. If additional use cases need to be satisfied, a full SPARQL Update solution can be used.

    Terminology

    Partial Update - The HTTP operation to modify only a subset of the triples for a given resource.

    Patch - See Partial update

    Patch document - Representation of the patch request indicating which updates (insertions or deletions) should be performed on a given resource.

    Use Cases & Requirements

    Use Cases:

    • Given a URI for a Change Request resource, I’d like to add a link to a related Test Plan. If the link already exists, then do nothing.
    • Given a URI for a Test Case resource, I’d like to replace all the blocking Defect links with the set of the Defect links I have (from a picked list of existing Defects from various providers).
    • Given a URI for a Test Case resource, I’d like to remove only one blocking Defect link whether it exists or not.
    • Given a URI for a Change Request resource, I’d like to update the link label (blank node) associated with the related Test Plan link.

    Requirements:

    • Add triples to an existing resource
    • Delete triples from a resource
    • Updating the object of a triple in a resource
    • Update reified statements on links, such as link labels
    • Guidance on collision detection
    • Reduce possibility of errors in updates because partial updates are safer than complete replace operations
    • Reduce bandwidth used and load on server because partial updates are smaller

    HTTP PATCH

    Patch Model

    OSLC clients SHOULD use the HTTP PATCH method to apply a partial update. If a server does not support PATCH on a resource, then it SHOULD respond with HTTP status code 405 (Method not allowed). If a server does support PATCH on a resource, then it SHOULD respond to a HTTP HEAD or OPTIONS operation with at least the token value "PATCH" for the response header Allow.

    For servers that support partial update but not the HTTP PATCH verb, an OSLC server MAY accept HTTP POST requests with the HTTP header X-Method-Override: PATCH to indicate that the request is a HTTP PATCH.

    OSLC Partial Update servers MUST treat a single HTTP PATCH request as a single resource update operation and not as independent insert and delete operations.

    OSLC Partial Update servers MUST treat HTTP PATCH request, on an existing resource identified by the canonical Request-URI, as an atomic modification to that resource. The patch model is limited to resources that are identified by their URI that typically maps to the subject of triples. HTTP PATCH of a resource is symmetric with the usage HTTP verbs of GET, PUT and DELETE which operate on a resource identified by the Request-URI.

    OSLC Partial Update servers MAY choose to allow the creation of new resources using HTTP PATCH. HTTP POST is the RECOMMENDED method for creating new resources.

    OSLC clients SHOULD use the HTTP If-Match header and HTTP ETags to ensure it is not modifying a resource that has changed since the client last retrieved its representation. OSLC servers SHOULD require the HTTP If-Match header and HTTP ETags to detect collisions. OSLC servers MUST respond with status code 412 (Condition Failed) if ETags fail to match if there are no other errors with the request. RFC2616

    A pre-defined named graph that represents the nodes to match or to insert is sufficient.
    The semantics of the PATCH model are based on SPARQL Update. Namely the subset of SPARQL Update is limited to:

    This model does not handle updating resources across multiple named graphs. Separate HTTP PATCH requests to each resource’s graph would need to be performed or utilizing a different method, such as SPARQL Update.

    Patch Document

    To use HTTP PATCH a client must provide with the request a Patch Document format that is able convey the change to be match in the partial update. This guidance recommends the use of named graph (quad) formats for the patch document. In this way, it does not require a new format or parsers to be created. Some quad formats available include TriG (Turtle-based) and TriX (XML-based).

    Proposed RESOLUTION: Since Core 2.0 requires RDF/XML it would make sense that those implementations would use TriX. For Core 3.0 (W3C LDP based), which requires Turtle, it would make sense that those implementations would use TriG (plus n-quads ).

    Insert triples about a resource

    Named graph URI: http://open-services.net/ns/core#insertGraph

    To insert new triples to a resource (graph), an OSLC client issues an HTTP PATCH request to the resource identified by the canonical Request-URI and request content of a Patch Document. The Patch Document indicates the insertion command by naming the graph http://open-services.net/ns/core#insertGraph and providing the triples to be inserted within that graph. In this case we use the SPARQL Update INSERT DATA command to specify the statements (triples) wish to insert.

    OSLC Partial Update servers MUST support inserting triples using the within the http://open-services.net/ns/core#insertGraph named graph following the semantics of INSERT DATA command as defined by SPARQL Update.

    Example - Simple insertion

    Here’s an example a client request to add new property values of dcterms:description and ex:status to a file or directory resource with URL of http://example.com/tasks/27.

    Before PATCH

    <http://example.com/tasks/27> <http://purl.org/dc/terms/modified> "1996-09-16T08:42:11.265Z" .
<http://example.com/tasks/27> <http://example.com/ns/terms/relatedTo> <http://example.com/resources/1> .

    Patch Document

    @prefix dcterms: <http://purl.org/dc/terms/>.
@prefix ex: <http://example.com/ns/terms#>.
<http://open-services.net/ns/core#insertGraph> { 
  <http://example.com/tasks/27> dcterms:description "Need to update Website owners as of May 2012" .
  <http://example.com/tasks/27> ex:status "PENDING" .
}

    After PATCH

    <http://example.com/tasks/27> <http://purl.org/dc/terms/description> "Website owners as of May 2012" .
<http://example.com/tasks/27> <http://example.com/ns/terms/status> "PENDING" .
<http://example.com/tasks/27> <http://purl.org/dc/terms/modified> "2012-05-21T17:02:13.265Z" .
<http://example.com/tasks/27> <http://example.com/ns/terms/relatedTo> <http://example.com/resources/1> .

    SPARQL Update mapping

    ToDo: Provide mapping details

    And here’s an example of adding a new dcterms:contributor value to a resource with URL of http://example.com/tasks/27. Note that the property has a value that is a blank-node of type foaf:Person. Also note that the subject of some of the triples is not the resource, but instead a blank-node reference.

    <http://open-services.net/ns/core#insertGraph> { 
  <http://example.com/tasks/27> <http://purl.org/dc/terms/contributor> _:bnode1 .
  _:bnode1 <http://www.w3.org/1999/02/22-rdf-syntax-ns#type> <http://xmlns.com/foaf/0.1/person> .
  _:bnode1 <http://xmlns.com/foaf/0.1/name> "Fernando Jones" .
}

    SPARQL Update mapping

    ToDo: Provide mapping details

    Delete triples from a resource

    Named graph URI: http://open-services.net/ns/core#deleteGraph

    To delete triples from a resource, a client will HTTP PATCH the in Patch Document (see examples below) to the resource URI with HTTP Header `Content-Type: application/x-trig’. In this case we use the SPARQL Update DELETE DATA command to specify the statements (triples) wish to remove.

    OSLC server implementations that support for Partial Update MUST support removing triples using the DELETE DATA command as defined by SPARQL Update.

    Example - Simple delete triples

    Here’s an example of what a client would patch to remove a triple from the resource at URL http://example.com/tasks/27.

    Before PATCH

    <http://example.com/tasks/27> <http://purl.org/dc/terms/description> "Website owners as of May 2012" .
<http://example.com/tasks/27> <http://example.com/ns/terms/status> "PENDING" .
<http://example.com/tasks/27> <http://purl.org/dc/terms/modified> "2012-05-21T17:02:13.265Z" .
<http://example.com/tasks/27> <http://example.com/ns/terms/relatedTo> <http://example.com/resources/1> .

    Patch Document

    @prefix ex: <http://example.com/ns/terms#>.
<http://open-services.net/ns/core#deleteGraph> { 
   <http://example.com/tasks/27> ex:relatedTo <http://example.com/resources/1> .
}

    After PATCH

    <http://example.com/tasks/27> <http://purl.org/dc/terms/description> "Website owners as of May 2012" .
<http://example.com/tasks/27> <http://example.com/ns/terms/status> "PENDING" .
<http://example.com/tasks/27> <http://purl.org/dc/terms/modified> "2012-05-21T17:27:42.265Z" .

    SPARQL Update mapping

    ToDo: Provide mapping details

    Updating the object of triples

    To update objects of triples for a resource, a client will send a HTTP PATCH request (see below) to the resource Request-URI with HTTP Header Content-type: application/x-trig or Content-type: application/trix+xml. In this case we use a SPARQL Update DELETE DATA command followed by an INSERT DATA command to specify the triples to be updated, the old triples and the new triples.

    OSLC Partial Update servers MUST support updating triples using the DELETE DATA and INSERT DATA commands as defined by SPARQL Update.

    OSLC Partial Update servers MAY allow only the the update of only those triples who’s subject is the HTTP Request-URI.

    Example - Simple update

    Before PATCH

    TBD

    Patch Document

    @prefix ex: <http://example.com/ns/terms#>.
<http://open-services.net/ns/core#deleteGraph> { 
  <http://example.com/files/file1> ex:parent <http://example.com/resources/1>.
  <http://example.com/files/file1> ex:favoriteTeam <http://example.com/teams/brazil>.
}
<http://open-services.net/ns/core#insertGraph> {
  <http://example.com/files/file1> ex:parent <http://example.com/resources/2>.
  <http://example.com/files/file1> ex:favoriteTeam <http://example.com/teams/paraguay>.
}

    After PATCH

    TBD

    SPARQL Update mapping

    ToDo: Provide mapping details

    Before PATCH

    @prefix ex: <http://example.com/bugtracker> .
@prefix oslc: <http://open-services.net/ns/core#> .
@prefix oslc_cm: <http://open-services.net/ns/cm#> .
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix dcterms: <http://purl.org/dc/terms/> .

<http://example.com/bugs/2314>
   a oslc_cm:ChangeRequest ;
   dcterms:identifier " 00002314 " ;
   oslc:shortTitle "Bug 2314" ;
   dcterms:title "Invalid installation instructions" ;
   oslc:instanceShape <http://example.com/shapes/defect> ;
   dcterms:description "Invalid installation instructions indicating invalid patches to be applied." ;
   oslc:discussedBy <http://example.com/bugs/2314/discussion> ;
   oslc_cm:relatedChangeRequest <http://myserver/mycmapp/bugs/1235> ,
      <http://remoteserver/mycmapp/defects/abc123> ;
   ex:priority " Medium " ;
   ex:severity " Normal " .

_:b1 dcterms:title "A bad link title";
   rdf:object <http://myserver/mycmapp/bugs/1235>;
   rdf:predicate oslc_cm:relatedChangeRequest;
   rdf:subject <http://example.com/bugs/2314>;
   a rdf:Statement.

    Patch document as TriG

    @prefix ex: <http://example.com/bugtracker>. 
@prefix oslc: <http://open-services.net/ns/core#>. 
@prefix oslc_cm: <http://open-services.net/ns/cm#>. 
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix dcterms: <http://purl.org/dc/terms/>.

oslc:deleteGraph { 
_:b1 dcterms:title "A bad link title";
   rdf:object <http://myserver/mycmapp/bugs/1235>;
   rdf:predicate oslc_cm:relatedChangeRequest;
   rdf:subject <http://example.com/bugs/2314>;
   a rdf:Statement.
}
oslc:insertGraph {
_:b1 dcterms:title "A very good link title";
   rdf:object <http://myserver/mycmapp/bugs/1235>;
   rdf:predicate oslc_cm:relatedChangeRequest;
   rdf:subject <http://example.com/bugs/2314>;
   a rdf:Statement.
}

    After PATCH

    TBD

    Mapped to SPARQL Update

    prefix ex: <http://example.com/bugtracker> 
prefix oslc: <http://open-services.net/ns/core#> 
prefix oslc_cm: <http://open-services.net/ns/cm#> 
prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> 
prefix dcterms: <http://purl.org/dc/terms/> 

DELETE {?s dcterms:title ?o . }
INSERT  {?s dcterms:title "A very good link title". } 
WHERE {
   ?s rdf:object <http://myserver/mycmapp/bugs/1235> .
   ?s rdf:predicate oslc_cm:relatedChangeRequest .
   ?s rdf:subject <http://example.com/bugs/2314> .
   ?s dcterms:title ?o .
}

    Before PATCH

    TBD

    Patch document as TriG

    @prefix oslc: <http://open-services.net/ns/core#>. 
@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#>.
@prefix dcterms: <http://purl.org/dc/terms/>.

oslc:deleteGraph {
_:b1 dcterms:title "A very good link title";
   rdf:object <http://myserver/mycmapp/bugs/1235>;
   rdf:predicate oslc_cm:relatedChangeRequest;
   rdf:subject <http://example.com/bugs/2314>;
   a rdf:Statement.
}

    After PATCH

    TBD

    Mapped to SPARQL Update

    prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> 
prefix dcterms: <http://purl.org/dc/terms/> 

DELETE  {?s dcterms:title "My special link title". } 
WHERE {
   ?s rdf:object <http://myserver/mycmapp/bugs/1235> .
   ?s rdf:predicate oslc_cm:relatedChangeRequest .
   ?s rdf:subject <http://example.com/bugs/2314> .
   ?s dcterms:title ?o .
}

    Note: a clever server may decide to remove the additional reification triples if decides there are no other interesting facts that they hold.

    Appendix A: Notices and References

    Contributors

    • SteveSpeicher (IBM, OSLC-Core Lead)
    • Arthur Ryman (IBM, OSLC-Core)
    • Nick Crossley (IBM, OSLC-Core)

    Reporting Issues on the Specification

    The working group participants who author and maintain this working draft specification, monitor a distribution list where issues or questions can be raised, see Core Mailing List

    Also the issues found with this specification and their resolution can be found at Core Issues.

    License and Intellectual Property

    We make this specification available under the terms and conditions set forth in the site Terms of Use, IP Policy, and the Workgroup Participation Agreement for this Workgroup.

    References

    Category:Supporting Documents

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