[OSLC-RM] Link types

Wed Oct 7 08:11:17 EDT 2009

I absolutely agree.  A uniform linking approach is critical to cross domain
collaboration.

The problem is that most of the new OSLC workgroups are on the hook to
provide a 1.0 specification by the end of this calendar year.  The
governing philosophy of the OSLC has been to deliver small sets of
specifications that provide value immediately, and that can be built on
later.

With that said we can either skip any attempt to define how links can be
managed, since it will most likely change once things are consolidated
later (the OSLC is working on providing common specifications across all
domains).  Or we can provide something that is useable now, but will most
likely have to be changed later.

If we don't do anything now, the spec will be incomplete with respect to
the essential use cases, since it will require additional knowledge of the
implementing system to be able to manage links, and that is essentially
another form of point-to-point integration that we see across the tools
today.  If we do specify either a flexible approach, or just define a fixed
set of what we consider common link types, then clients built to this spec
will have to change (possibly losing functionality) when the later ones
come out.

<jim/>

jim conallen
jconallen at us.ibm.com
Rational Software, IBM Software Group

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  |"Simon Wills" <simon.wills at integrate.biz>                                                                                                         |
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  |"Ian Green1" <ian.green at uk.ibm.com>, James Conallen/Philadelphia/IBM at IBMUS                                                                        |
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  |<oslc-rm at open-services.net>                                                                                                                       |
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  |10/07/2009 07:47 AM                                                                                                                               |
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  |RE: [OSLC-RM] Link types                                                                                                                          |
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Hi:

I think that there are three distinct issues here, namely:

      a.       Whether there is a need for a uniform approach to defining
      link-related resources across OSLC;
      b.      Whether we attempt to define a minimal set of standardised
      link types;
      c.       Assuming that we *do* adopt a uniform approach to linking
      across OSLC, how and when we do so.
Of these points, deciding whether or not to implement a uniform linking
model is by far and away the most important.  Standardising link labels is
a ‘nice to have’ that follows on from this first decision (this was the
main focus of the RM discussion document), but is something that we can
live without.  And the last point is to do with implementation.

Ben’s interests (i.e. reporting) provide a good illustration of the key
issue.  If I understand correctly, he wants to be able to generate reports
about lifecycle artefacts, some of which may require him to traverse links
between artefacts, without having to make allowances for the domains in
which those artefacts live.  This seems to me to be entirely reasonable –
and reporting isn’t the only domain for which this expectation holds.

OSLC stands for Open Services for Lifecycle Collaboration.  Lifecycle
collaboration requires that we leverage relationships between lifecycle
artefacts.  If we don’t tackle the issue of uniformity in the handling of
links, we risk ending up with a series of poorly connected domain islands,
each with its own domain-specific linking paradigm.  Surely there is a
prima facie case to recognise that links are the things that tie these
domains together, and hence that the definition of link-related resources
and their behaviour should be common across all OSLC domains?

Best regards

Simon

From: oslc-rm-bounces at open-services.net [
mailto:oslc-rm-bounces at open-services.net] On Behalf Of Ian Green1
Sent: 07 October 2009 11:39
To: James Conallen
Cc: oslc-rm at open-services.net
Subject: Re: [OSLC-RM] Link types

Hello Jim,

I think your description of how OSLC links currently work in the defining
of a relationship is accurate.  There has been some discussion about the
merit of such a design, since it is exposed to a fragility, namely, that
for each link, there should be a corresponding link in the other direction.
The need for the "backlink" as it has been called, aids navigability (we
typically want the relationship to be navigable in both directions).  It is
also reasonably easy to implement.

The fragility is maintaining this invariant: for example, when a resource
is deleted, any "backlinks" to that resource should be removed. There are
other "relationship management" designs which don't have this weakness.

My reading of Simon's document is that it is talking about these
relationships, rather than the lower-level "nuts and bolts" of how one
resource links to some other resource.   We need to think about how we can
uniformly manage these relationships across all the domains.

best wishes,
   -ian

ian.green at uk.ibm.com (Ian Green1/UK/IBM at IBMGB)
Chief Software Architect, Requirements Definition and Management
IBM Rational

 From:     James Conallen <jconallen at us.ibm.com>                           

 To:       Benjamin Williams/UK/IBM at IBMGB                                  

 Cc:       Ian Green1/UK/IBM at IBMGB, oslc-rm at open-services.net              

 Date:     06/10/2009 16:44                                                

 Subject:  Re: [OSLC-RM] Link types                                        

I have one concern about the link types document's attempt to define *both*
the forward and reverse links. I believe that the general OSLC mechanism
for creating bi-directional links is to create two unidirectional links
managed by each server, and hope that it is possible with a query on the
other server to find the right back link when deleting.

If this is the case, then we should probably restrict the definition of the
link types to those that are managed by the OSLC RM implementing service,
and not make assumptions that all the other services (i.e. OSLC CM, OSLC
AM, OSLC QM, ...) will support these OSLC RM defined link types.

In the OSLC AM space our scenarios have all sorts of link types that are
referenced. For example a model element can implement a requirement, or
specify a requirement, or a requirement resource can be documentation (i.e.
how to guide) for a model element. Given that both models and requirements
can be used in many different ways, it is hard to pin down, generically,
just a few relationship types between AM resources and requirements. With
this said, if we just say that links from Requirements to Architecture
Management Resources will be one of (modeledBy, realisedBy or
incorporatedBy) that will be fine from an OSLC AM client point of view.

<jim/>

jim conallen
jconallen at us.ibm.com
Rational Software, IBM Software Group

Inactive hide details for Benjamin Williams ---10/06/2009 10:22:09 AM---Ian
As per my other email on reporting, I feel that sucBenjamin Williams
---10/06/2009 10:22:09 AM---Ian As per my other email on reporting, I feel
that such such collaboration

 From:    Benjamin Williams <bwilliams at uk.ibm.com>                         

 To:      Ian Green1 <ian.green at uk.ibm.com>                                

 Cc:      oslc-rm at open-services.net, oslc-rm-bounces at open-services.net     

 Date:    10/06/2009 10:22 AM                                              

 Subject: Re: [OSLC-RM] Link types                                         

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

Ian

As per my other email on reporting, I feel that such such collaboration and
consistency across domains will be extremely important, if not absolutely
necessary.
Specifically in the context of reporting, the features exposed by service
providers across each domain will need to (consistently) support the
requirements and use-cases defined in the Reporting domain such that
reporting consumers can leverage lifecycle data without needing any
knowledge of the source domains and any differences in the way they expose
data.

The scenarios and use-cases that we are defining in the reporting domain
should be entirely domain agnostic, as far as I am concerned. We can use
specific examples for both single domain reporting as well as cross domain
reporting, but the domains used in the examples should be freely
interchangeable without any impact on the reporting consumer.

The reporting domain is still in its infancy, and my involvement in OSLC is
only just beginning, but from what I understand, the reporting domain might
be one of the first things to force us to think about some of the cross
domain issues that you and Simon have discussed.

/Ben

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

Benjamin Williams
Senior Product Manager - Rational Publishing Engine

Email: bwilliams at uk.ibm.com
Tel: +44 20 8818 4360
Cell: +44 7710 637 067
IBM Extension: 364360
IBM ITN: 37364360
-----------------------------------------------------------------------------

 From:        Ian Green1/UK/IBM at IBMGB                                      

 To:          "Simon Wills" <simon.wills at integrate.biz>                    

 Cc:          oslc-rm at open-services.net                                    

 Date:        06/10/2009 14:16                                             

 Subject:     Re: [OSLC-RM] Link types                                     

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

Hello Simon,

this is good progress both on explaining our current position w.r.t. link
types, and also taking a longer term view of the role we see link types
playing the future. Thanks very much for putting this together.

Steve/Scott: whilst there is no pressure as yet to drive this forward,
Simon makes a good case for any such effort to be cross-OSLC domains. How
do you see this shaping up over time? Is there some tension between
designing an OSLC-wide vocabulary and being entirely scenario-driven?

best wishes,
-ian

ian.green at uk.ibm.com (Ian Green1/UK/IBM at IBMGB)
Chief Software Architect, Requirements Definition and Management
IBM Rational

 From:        "Simon Wills" <simon.wills at integrate.biz>                    

 To:          Ian Green1/UK/IBM at IBMGB                                      

 Date:        05/10/2009 15:42                                             

 Subject:     Link types                                                   

Hi Ian

Just to let you know ... I’ve put a new section titled ‘Discussion Topics’
in the right hand sidebar of the main RM page, and put a link to a
discussion document on link types (at
http://open-services.net/bin/view/Main/RmDiscussionLinkTypes). Haven’t
quite sussed out how to format tables properly in the Wiki editor, but the
content is all there.

Would you like me to put out an announcement on the mailing list?

Cheers

Simon

Simon Wills
Managing Director
integrate systems engineering ltd
m: +44 (0)7967 091824
t: +44 (0)1225 859991
f: +44 (0)1225 859993
e: simon.wills at integrate.biz
w: www.integrate.biz

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