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

[Martin Nally]

I agree, Arthur. I think that it's OK for a client to "demand compliance"
of a resource that uses the RDF type from a domain, so long as the client
is thoughtful about what compliance will mean over time as the spec
evolves. I think the trap to avoid is assuming compliance across a
relationship based on the predicate of the relationship, instead of based
on the resource that is discovered at the other end of the relationship

Best regards, Martin

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


Arthur Ryman/Toronto/IBM wrote on 12/16/2010 05:23:54 PM:

> [image removed]
>
> Re: [oslc-core] Oslc-Core Digest, Vol 11, Issue 24
>
> Arthur Ryman
>
> to:
>
> Martin Nally
>
> 12/16/2010 05:35 PM
>
> Cc:
>
> oslc-core, oslc-core-bounces
>
> 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
>
> [image removed]
>
> 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
>
> [image removed]
>
> 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:
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>    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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> End of Oslc-Core Digest, Vol 11, Issue 24
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