Re: Link profiles


Gentry, Edward <e.gentry@...>
 

A few ideas and observations and a concrete proposal:

 

  • A helpful idea was proposed by our French Sodius Colleague whose name escapes me.  He suggested in a conversation after our last call – and he’ll correct me if I don’t represent him well - that resource shapes should be extended so that tools could indicate which links they index.

 

  • @Jim Amsden’s  suggestion is also interesting (again he’ll correct me if I don’ represent him well) Each “link” might be represented as a pair of reciprocal predicates. For example: Let  (P and P’) be a pair of reciprocal predicates.  Then semantically, the triple (S0, P, O0), would have the same meaning the triple (O0, P’, S0).

 

  • Also I’d observe that “links” already have the concept of a reciprocal-names. Let N be the name for the P in triple (S0, P, O0) when viewed from the perceptive of S0. Then N’, the reciprocal-name is the title of P, is the title of P when it is viewed from the perspective of O2. Naturally if we had reciprocal predicates then the name of P’ (above) would be N’.

 

Besides discussing these more in detail, I’d like to make the following suggestion: We should reify the concept of link beyond just a single predicate – indeed above are examples of where we are already doing this. We should formalize what we mean by links, want kind of characteristics they may have: titles, reciprocal-links, reciprocal-labels, etc.

 

However has  @Eran Gery has emphasized all of this is beyond the scope of the first version of Link Profiles.

 

For me the link profile work would look something like this:

 

Version 0: Describe linking as it exists in ELM today keeping modifications to a minimum. Given the importance of GC’s for real life applications – and changing my position a bit here – this should include both opt in and opt out cases (with and out GCS), even though that means waving our hands a bit and just assuming the indexing for back links.  

 

Version 1: We reify links and include the concepts above and more.

 

 

From: Gentry, Edward <e.gentry@...>
Sent: Donnerstag, 26. Mai 2022 22:48
To: Jim Amsden <jamsden@...>; Robert Baillargeon <rbaillargeon@...>; Andrii Berezovskyi <andriib@...>; Eran Gery <eran.gery@...>; oslc-op@...; David Honey2 <david.honey@...>
Subject: Re: [oslc-op] Link profiles

 

Sorry I’ve missed the discussion today. It’s a holiday here. 

 

One thing for me is very clear. If by link we mean a single predicate then we always know where it is stored. Always. It is stored with the subject of the link. Always. 

 

We don’t store statements about resources we don’t control. And I certainly should not trust a statement made by another about a resource that belongs to me. 

 

Now if we understand a link more semantically then Jim’s suggestion that the concept “satisfies” could be expressed with two different predicates “satisfies” and “satisfies by” each potentially stored on the corresponding side is something we might consider. But I’d suggest as a second phase since nothing like this exists to my knowledge 


From: Jim Amsden <jamsden@...>
Sent: Thursday, May 26, 2022 9:33:00 PM
To: Robert Baillargeon <
rbaillargeon@...>; Andrii Berezovskyi <andriib@...>; Eran Gery <eran.gery@...>; Gentry, Edward <e.gentry@...>; oslc-op@... <oslc-op@...>; David Honey2 <david.honey@...>
Subject: RE: [oslc-op] Link profiles

 

I am specifically not proposing to store backlinks. What I’m suggesting is that which link is the forward link depends on the use case the servers are trying to support. So rather I’m proposing using constraints as a means of discovering and perhaps specifying in a profile, what the links mean in a particular situation.

 

Once discovered where the link is stored, there should be standard way of determining the incoming/inverse link.

 

 

From: Robert Baillargeon <rbaillargeon@...>
Date: Thursday, May 26, 2022 at 3:12 PM
To: Jim Amsden <
jamsden@...>, Andrii Berezovskyi <andriib@...>, Eran Gery <eran.gery@...>, "e.gentry@..." <e.gentry@...>, "oslc-op@..." <oslc-op@...>, David Honey2 <david.honey@...>
Subject: [EXTERNAL] Re: [oslc-op] Link profiles

 

I'm always for only storing the forward link. It has a clear advantage in the ability to better manage the configurations and the composition of configurations. If I could get rid of backlinks I would. ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍ ‍

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I'm always for only storing the forward link.  It has a clear advantage in the ability to better manage the configurations and the composition of configurations.  If I could get rid of backlinks I would. 

 

When moving entirely to reverse link discovery, I would also note that we will need to have some behaviors in the tools to address when a discovery task fails due to downstream authentication, timeout, or otherwise.  We have seen situations where the inverse link is not visible and user confusion about the cause.

 

That is an interesting thought that we could discover link ownership by inspecting the shape.  Let me consider that path and see if that is complete with the information we would expect.

 

 

 

The other interesting point is to 

Chief Product Officer – Linked Data

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Ph: 716 261 8338 
sodiuswillert.com

 

 

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From: oslc-op@... <oslc-op@...> on behalf of David Honey2 via lists.oasis-open-projects.org <david.honey=ibm.com@...>
Sent: Thursday, May 26, 2022 2:59 PM
To: Jim Amsden <
jamsden@...>; Andrii Berezovskyi <andriib@...>; Eran Gery <eran.gery@...>; e.gentry@... <e.gentry@...>
Cc:
oslc-op@... <oslc-op@...>
Subject: Re: [oslc-op] Link profiles

 

Always trying to create both forward and back links seems like the wrong thing to do, even in opt-out mode. Servers are free to either silently ignore RDF properties it doesn’t support, or to fail the whole PUT if it contains an unsupported property. That could give rise to unpredictable behaviour.

 

An OSLC client may be able to discover which direction(s) are to be used. Consider a user wanting to create a validates requirement link between a test case and a requirement. There are two potential links (as defined by OSLC specs):

  • oslc_qm:validatesRequirement stored on the test case
  • oslc_rm:validatedBy stored on the requirement

 

A caller can GET the test case, look for its oslc:instanceShape, get that shape, and then look for the presence or absence of an OSLC property for oslc_qm:validatesRequirement. It can then GET the requirement, look for its oslc:instanceShape, get that shape, and then look for the presence or absence of an OSLC property for oslc_rm:validatedBy.

I wonder whether that’s sufficient to do the right thing for ELM and for other applications.

 

Thinking about the opt-in case….

Say you have requirement R1 version 1 (R1-1), and test case TC1 version 1 (TC1-1).
You update the test case in the context of some ETM stream, creating TC1-2 that has a
oslc_qm:validatesRequirement link to the concept R1. In order to create the back-link, you’d need to update R1-1 in the context of a DNG stream, to create R1-2. A caller won’t know which stream to use for that backlink, so the only way I can see this working is if this is done in a GC context. It also has the side-effect of creating a new version of both the source and the target. If someone looked at R1 in a GC context that resolved to R1-1, and resolved TC1 to TC1-2, you end up with an inconsistency. The oslc_rm:validatedBy link didn’t exist on R1-1, but the forward link to that requirement exists on TC1-2. I think these were the reasons why ELM decided for opt-in, there would be no backlinks.

 

David.

 

From: Jim Amsden <jamsden@...>
Sent: 26 May 2022 18:46
To: Andrii Berezovskyi <andriib@...>; Eran Gery <eran.gery@...>; David Honey2 <david.honey@...>; e.gentry@...
Cc: oslc-op@...
Subject: Re: [EXTERNAL] Link profiles

 

This is a good start, but we should understand how it supports the use cases and common practice.

 

On the issues we’ve been discussing on links: the OSLC specifications define vocabularies and shapes that specify links that would be reasonably considered inverses. Requirement validatedBy TestCase and TestCase validatesRquirement Requirement is one such example. However, OSLC does not specify which one is the property, which would be considered the inverse property, which or  “owed by” any particular server that supports RM and/or QM domains. Rather this is a server implementation decision, often driven by use cases/scenarios that support a particular work-flow – i.e., requirements vs. test driven develop in this case.

 

Fundamentally OSLC ResourceShape constraints have no way of indicating what a server expects to store vs. expects another server involved in a link relationship expects/can/has to store. So, implementations do what works for them and what is stored where must be documented outside OSLC discovery.

 

Added to that, OSLC delegated dialogs don’t establish a clear distinction between the requester and provider of the delegated dialog and who’s supposed to “own” the link – that is, which link property the pair of tools considers the actual source and target of the link, and whether the source or target resource will be the subject of the link property triple.

 

Jazz.net tools attempt to make this transparent, so the user doesn’t have to know which server is storing the link, or how the incoming links are stored or calculated. This is purely a usability issue. However, the participating servers do have to know because even through the creation of the link can be created from either direction, the servers must know which one stores it and implement the link creation accordingly. Again, there is no way to discover this.

 

We could expand ResourceShape to define inverse property constraints to provide a discoverable way for clients and servers to interoperate when creating links from either direction. I expect that might be a better approach than defining a number of profile special cases.

 

 

 

From: Andrii Berezovskyi <andriib@...>
Date: Thursday, May 26, 2022 at 11:49 AM
To: Eran Gery <
eran.gery@...>, David Honey2 <david.honey@...>, Jim Amsden <jamsden@...>, "e.gentry@..." <e.gentry@...>
Cc: "
oslc-op@..." <oslc-op@...>
Subject: [EXTERNAL] Link profiles

 

Hi, I put together a simple table for the possible profiles after the call: https://docs.google.com/spreadsheets/d/1fjjGvHrv2yPru8S_6HNoJ5atn6617cUfFUDRz5xAfKQ/edit?usp=sharing Please look at them and tell me what you think. Thanks to Eran

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Hi,

 

I put together a simple table for the possible profiles after the call: https://docs.google.com/spreadsheets/d/1fjjGvHrv2yPru8S_6HNoJ5atn6617cUfFUDRz5xAfKQ/edit?usp=sharing

 

Please look at them and tell me what you think. Thanks to Eran for taking extra time to explain some things to me.

 

/A

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