[oslc-core] Oslc-Core Digest, Vol 11, Issue 24

Thu Dec 16 17:35:28 EST 2010

Martin,

I completely agree about the potential for misapplication of UML/OO 
concepts to web architecture, especially those that assume a closed world 
and tight coupling. 

That being said, it is consistent with web architecture principles and RDF 
for OSLC to define the semantics of URIs that belong to our namespace. In 
the case of type URIs, one extreme is to say nothing; the other is to 
demand compliance with a domain spec. It may be more useful to define a 
middle ground.

Regards, 
___________________________________________________________________________ 

Arthur Ryman, PhD, DE

Chief Architect, Project and Portfolio Management
IBM Software, Rational
Markham, ON, Canada | Office: 905-413-3077, Cell: 416-939-5063

From:
Martin Nally/Raleigh/IBM at IBMUS
To:
Arthur Ryman/Toronto/IBM at IBMCA
Cc:
oslc-core at open-services.net, oslc-core-bounces at open-services.net
Date:
12/16/2010 12:36 PM
Subject:
Re: [oslc-core] Oslc-Core Digest, Vol 11, Issue 24

Thanks, Arthur - I wasn't aware of the versioning section of the spec.

I completely agree with your comment about unexpected responses. I think 
we need to keep reminding ourselves of this. I'm sensitive to this issue 
because I see a recurring pattern of people carrying over incorrect 
assumptions that they are used to making from previous systems they have 
worked on. For example, I spoke to a group that was very surprised to 
learn that OSLC does not guarantee that if you follow a link from a 
resource that conforms to one OSLC domain (for example the link from an 
OSLC test case to the requirement that it validates) that you will 
necessarily land on a resource that conforms to some other compatible 
domain spec (for example the requirement spec). People who are steeped in 
a UML history are used to making exactly this assumption, which is one of 
the reasons I wince when I see UML diagrams connecting the OSLC domains. 
The problem with the UML assumption is that it creates a closed system, 
and all the domains reference each other transitively, so no single domain 
can be adopted without implicitly adopting all the others by transitive 
closure. This creates the sort of tight couplings that OSLC is trying to 
avoid.

Best regards, Martin

Martin Nally, IBM Fellow
CTO and VP, IBM Rational
tel: +1 (714)472-2690

From:
Arthur Ryman/Toronto/IBM at IBMCA
To:
Martin Nally/Raleigh/IBM at IBMUS
Cc:
oslc-core at open-services.net, oslc-core-bounces at open-services.net
Date:
12/15/2010 03:45 PM
Subject:
Re: [oslc-core] Oslc-Core Digest, Vol 11, Issue 24

Martin,

I agree that clients should be able to gracefully handle unexpected 
responses. 

Do you disagree with the statement in general, or just when the 
complications of versioning are considered, i.e. "If a service claims to 
comply with a domain spec then resources returned by that service must 
comply with the domain spec"

The OSLC Core does have a mechanism for requesting or specifying the 
version via the OSLC-Core-Version HTTP header. [1] The mechanism allows 
the service to return a version of a resource that the client can handle. 
It is therefore meaningful to talk about the version of the service, but 
this may include support for back-levels of the service too. Even though 
resources may have been created by different versions of the service, the 
service has a mechanism for returning a version of a resource that is 
compatible with the client. I assume that domain specs could define 
version headers specific to them.

[1] 
http://open-services.net/bin/view/Main/OslcCoreSpecification?sortcol=table;up=#Specification_Versioning

Regards, 
___________________________________________________________________________ 

Arthur Ryman, PhD, DE

Chief Architect, Project and Portfolio Management
IBM Software, Rational
Markham, ON, Canada | Office: 905-413-3077, Cell: 416-939-5063

From:
Martin Nally/Raleigh/IBM at IBMUS
To:
Arthur Ryman <ryman at ca.ibm.com>
Cc:
oslc-core at open-services.net, oslc-core-bounces at open-services.net
Date:
12/14/2010 07:08 PM
Subject:
Re: [oslc-core] Oslc-Core Digest, Vol 11, Issue 24

I think this confirms that the only safe option for a client is to assume 
nothing. I think the spec should say this. I don't think it's even safe to 
assume that "the resources that you get from a service that claims to 
comply with a domain spec must comply with that domain spec". Let's assume 
I'm a client that is programmed to understand version n of the XYZ OSLC 
specification. If I access an XYZ service, I might find resources created 
from version 1 through version n+m of the domain spec stored within the 
same service, so it probably isn't even meaningful to talk about the 
version of the service, unless it means simply the version of its 
service/service provider document. Since I can't know in advance what 
changes were introduced in versions n+1 through n+m, I can't really say 
what it means for the resources to be compliant with a spec, so I'd better 
be prepared for the unexpected.

Best regards, Martin

Martin Nally, IBM Fellow
CTO and VP, IBM Rational
tel: +1 (714)472-2690

From:
Arthur Ryman <ryman at ca.ibm.com>
To:
Martin Nally/Raleigh/IBM at IBMUS
Cc:
oslc-core at open-services.net, oslc-core-bounces at open-services.net
Date:
12/14/2010 06:50 PM
Subject:
Re: [oslc-core] Oslc-Core Digest, Vol 11, Issue 24

Martin,

When Jim raised this topic initially, I pointed out that OSLC does not 
currently make any statement about how type URIs should be used outside 
their domain specs, i.e. you should assume that the resource satisfies the 

domain spec. All you can count on is the service, i.e. the resources that 
you get from a service that claims to comply with a domain spec must 
comply with that domain spec. However, it does seem natural that the type 
URIs (and any other property URIs) defined by one domain might be useful 
to other domains or other non-OSLC services. Since these type URIs are in 
the OSLC namespace, it seems appropriate that OSLC should specify their 
intended use, with the usual understanding that no organization can 
restrict how other organizations use URIs.

No, I didn't consider versioning. I assume the versioning rules are 
specified by each domain and so any user of the type URIs should comply 
with that. Yes, this could be a can of worms when a resource has more than 

one type URI since you'd have to specify the versions for each of the 
domains. This is a great topic for the "Mutli-Type" workgroup to discuss.

Regards, 
___________________________________________________________________________ 

Arthur Ryman, PhD, DE

Chief Architect, Project and Portfolio Management
IBM Software, Rational
Markham, ON, Canada | Office: 905-413-3077, Cell: 416-939-5063

From:
Martin Nally <nally at us.ibm.com>
To:
oslc-core at open-services.net
Cc:
oslc-core at open-services.net, oslc-core-bounces at open-services.net
Date:
12/10/2010 11:30 AM
Subject:
Re: [oslc-core] Oslc-Core Digest, Vol 11, Issue 24
Sent by:
oslc-core-bounces at open-services.net

>> the RDF representation of T SHOULD satisfy the OSLC Domain 
specification
that defines T.

Have you thought about what this means for versioning? Does this mean the
2.0 version of the OSLC specification? All past and future versions? I
think this will open a can of worms. I think we should make the opposite
statement - that when something says it is of some OSLC type, this carries
no guarantees whatever. Caveat emptor.

Best regards, Martin

Martin Nally, IBM Fellow
CTO and VP, IBM Rational
tel: +1 (714)472-2690

  From:       oslc-core-request at open-services.net 

  To:         oslc-core at open-services.net 

  Date:       12/09/2010 12:00 PM 

  Subject:    Oslc-Core Digest, Vol 11, Issue 24 

  Sent by:    oslc-core-bounces at open-services.net 

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Today's Topics:

   1. Re: Resources that have Multiple rdf:type Values (Arthur Ryman)

----------------------------------------------------------------------

Message: 1
Date: Wed, 8 Dec 2010 17:25:40 -0500
From: Arthur Ryman <ryman at ca.ibm.com>
To: Dave <snoopdave at gmail.com>
Cc: oslc-core at open-services.net
Subject: Re: [oslc-core] Resources that have Multiple rdf:type Values
Message-ID:

<OFBE176E2F.3D444635-ON852577F3.007A354B-852577F3.007B3507 at ca.ibm.com>
Content-Type: text/plain; charset="US-ASCII"

Dave,

I was pointing out the status quo. However, our desire is that types be
used in a predictable way.

I am recommending that we add an explicit statement to our spec to avoid
"capricious" use of OSLC-defined types. We don't "enforce" this via an
ontology so we need to provide explicit guidance in the Core spec.

Regards,
___________________________________________________________________________

Arthur Ryman, PhD, DE

Chief Architect, Project and Portfolio Management
IBM Software, Rational
Markham, ON, Canada | Office: 905-413-3077, Cell: 416-939-5063

From:
Dave <snoopdave at gmail.com>
To:
Arthur Ryman/Toronto/IBM at IBMCA
Cc:
oslc-core at open-services.net
Date:
12/08/2010 04:56 PM
Subject:
Re: [oslc-core] Resources that have Multiple rdf:type Values

On Wed, Dec 8, 2010 at 12:22 PM, Arthur Ryman <ryman at ca.ibm.com> wrote:
> At the Core telecon today, Jim raised this topic. We need to continue
the
> discussion. Here is a suggestion for how to handle this:
>
> Any RDF resource representation MAY contain zero or more triples that
have
> a given URI, S, as the subject, and rdf:type as the predicate,  If there
> is a triple of the form (S, rdf:type, T) where T is a type URI defined
by
> some OSLC Domain specification, then the RDF representation of T SHOULD
> satisfy the OSLC Domain specification that defines T.

I thought you argued against this point today, saying that you can
only make that sort of inference when you that a resource is provided
by a service that implements an OSLC specification.

- Dave

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