Minutes: https://github.com/oslc-op/oasis-open-project/blob/master/minutes/2022/2022-05-26.md

/Andrew

oslc-op Weekly Contributors Meeting

When:
06/09/2022
10:00am to 11:00am
(UTC-04:00) America/New York

Where:
https://meet.jit.si/oslc-op

Organizer: Jim Amsden jamsden@...

View Event

Description:
oslc-op contributors weekly telecon. 

Following the discussion today, please find attached the spreadsheet with the updates made during the call. The profiles in the second sheet are described in https://docs.google.com/spreadsheets/d/1fjjGvHrv2yPru8S_6HNoJ5atn6617cUfFUDRz5xAfKQ/edit#gid=0

Cell F22 in the second sheet is an “anomalous anomaly”, which requires TRS but not configuration management, I simply marked it with the Bidi profile + an ad-hoc TRS support requirement.

The idea of the table is too keep the product names in the row 8 and 19 as it and replace the product names in the column D with OSLC domain names to indicate in the future which profiles 3^rd-party tools need to support to integrate with the corresponding Jazz products.

Looking forward to your feedback.

/Andrew

Thu 2^nd June is a UK public holiday, so I won’t be attending the OSLC OP meeting.

I will look at this next week.

David

Can you please look up the link storage/discovery tables I sent and confirm? These tables are a practical basis to discuss the linking profile.

Would be great if you can do before tomorrow’s meeting… shouldn’t take you more than 5 minutes.

(See XL attachment to the original message)

Thanks

Eran

Hi David, all,

Again, pulling back towards the pragmatic principle “let’s define a profile that at least guarantees ELM (jazz) cross linking”.

Let’s push to the background for now discussions around “good architectural specification”. Profiles here are all about (ugly) pragmatics.

Note: there are some ELM anomalies we may not include in a profile, only document. Obviously we need ELM to fix that. Some examples:

-          ELM currently does not support AM/AM linking (RMM). Obviously we cannot enforce this in a profile. We are pushing hard to fix it this year.

-          While in opt-in mode incoming link discovery is done via LDX, RM expects AM to support OSLC query for that. This means that LDX support is not enough for an AM provider, and it needs to support both LDX feed and OSLC query. Again we can document it but recommend LDX usage across all opt-in incoming link discoveries.

-          In OptOut mode (no config) ELM assumes backlinking. So for example if a Jira connector creates a link to a requirement, it also needs to create a backlink on the requirement. Ouch.

So for that purpose a question about “opt out” mode: how does ELM behave here, between using a single link with incoming implemented with OSLC query, vs. using backlinks. As far as I recall, all CCM links are using backlinking, and other (RM:QM, RM:AM, AM:QM) use a query. Is that correct?

As for shapes based discovery: I think we also need to specify the storage policy, as creating apps based on discovery requires a higher level of sophistication and preparing for variability. Between two providers, if both have shapes that claim ownership, one need to concede. So to simplify we need to provide ownership map. Also another related question: do the shapes change between opt-out and opt-in mode? For example. RM in opt-out would keep a backlink to CCM. In opt-in not. Does it maintain two shapes?

Also for Anrew’s request attached is a spreadsheet  I created at the time for opt-in mode. We also need to create on for opt-out.  @David Honey2

Can you please confirm its accuracy?

Hope this makes sense…

Regards,

Eran

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.

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.

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

hi

I will also be away today.

Hi,

I will attend an off-site project meeting on Thursday and won’t be able to join the OP call. Please make sure to have someone take minutes.

/Andrew

Thu 2^nd June is a UK public holiday, so I won’t be attending the OSLC OP meeting.

I will look at this next week.

David

Can you please look up the link storage/discovery tables I sent and confirm? These tables are a practical basis to discuss the linking profile.

Would be great if you can do before tomorrow’s meeting… shouldn’t take you more than 5 minutes.

(See XL attachment to the original message)

Thanks

Eran

Hi David, all,

Again, pulling back towards the pragmatic principle “let’s define a profile that at least guarantees ELM (jazz) cross linking”.

Let’s push to the background for now discussions around “good architectural specification”. Profiles here are all about (ugly) pragmatics.

Note: there are some ELM anomalies we may not include in a profile, only document. Obviously we need ELM to fix that. Some examples:

• ELM currently does not support AM/AM linking (RMM). Obviously we cannot enforce this in a profile. We are pushing hard to fix it this year.
• While in opt-in mode incoming link discovery is done via LDX, RM expects AM to support OSLC query for that. This means that LDX support is not enough for an AM provider, and it needs to support both LDX feed and OSLC query. Again we can document it but recommend LDX usage across all opt-in incoming link discoveries.
• In OptOut mode (no config) ELM assumes backlinking. So for example if a Jira connector creates a link to a requirement, it also needs to create a backlink on the requirement. Ouch.

So for that purpose a question about “opt out” mode: how does ELM behave here, between using a single link with incoming implemented with OSLC query, vs. using backlinks. As far as I recall, all CCM links are using backlinking, and other (RM:QM, RM:AM, AM:QM) use a query. Is that correct?

As for shapes based discovery: I think we also need to specify the storage policy, as creating apps based on discovery requires a higher level of sophistication and preparing for variability. Between two providers, if both have shapes that claim ownership, one need to concede. So to simplify we need to provide ownership map. Also another related question: do the shapes change between opt-out and opt-in mode? For example. RM in opt-out would keep a backlink to CCM. In opt-in not. Does it maintain two shapes?

Also for Anrew’s request attached is a spreadsheet  I created at the time for opt-in mode. We also need to create on for opt-out.  @David Honey2

Can you please confirm its accuracy?

Hope this makes sense…

Regards,

Eran

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.

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.

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

David

Can you please look up the link storage/discovery tables I sent and confirm? These tables are a practical basis to discuss the linking profile.

Would be great if you can do before tomorrow’s meeting… shouldn’t take you more than 5 minutes.

(See XL attachment to the original message)

Thanks

Eran

Hi David, all,

Again, pulling back towards the pragmatic principle “let’s define a profile that at least guarantees ELM (jazz) cross linking”.

Let’s push to the background for now discussions around “good architectural specification”. Profiles here are all about (ugly) pragmatics.

Note: there are some ELM anomalies we may not include in a profile, only document. Obviously we need ELM to fix that. Some examples:

• ELM currently does not support AM/AM linking (RMM). Obviously we cannot enforce this in a profile. We are pushing hard to fix it this year.
• While in opt-in mode incoming link discovery is done via LDX, RM expects AM to support OSLC query for that. This means that LDX support is not enough for an AM provider, and it needs to support both LDX feed and OSLC query. Again we can document it but recommend LDX usage across all opt-in incoming link discoveries.
• In OptOut mode (no config) ELM assumes backlinking. So for example if a Jira connector creates a link to a requirement, it also needs to create a backlink on the requirement. Ouch.

So for that purpose a question about “opt out” mode: how does ELM behave here, between using a single link with incoming implemented with OSLC query, vs. using backlinks. As far as I recall, all CCM links are using backlinking, and other (RM:QM, RM:AM, AM:QM) use a query. Is that correct?

As for shapes based discovery: I think we also need to specify the storage policy, as creating apps based on discovery requires a higher level of sophistication and preparing for variability. Between two providers, if both have shapes that claim ownership, one need to concede. So to simplify we need to provide ownership map. Also another related question: do the shapes change between opt-out and opt-in mode? For example. RM in opt-out would keep a backlink to CCM. In opt-in not. Does it maintain two shapes?

Also for Anrew’s request attached is a spreadsheet  I created at the time for opt-in mode. We also need to create on for opt-out.  @David Honey2

Can you please confirm its accuracy?

Hope this makes sense…

Regards,

Eran

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.

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.

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

Hi,

I will attend an off-site project meeting on Thursday and won’t be able to join the OP call. Please make sure to have someone take minutes.

/Andrew

Well IBM/ELM/Jazz has a discovery namespace: http://jazz.net/xmlns/prod/jazz/discovery/1.0/

This was developed after 3.x because it of perceived architectural limitations of the rootservices. But rootservices was never deprecated so now Jazz has both.

The discovery service idea was actually pretty good. Applications contribute services to the JTS and the JTS allows these to be discovered. You can see some of this in the browser, also do GET on /rm/scr to see the contribution.

I suspect, that what your seeing is perhaps a relic of this, where the discovery idea was to be contributed to OSLC.

Could someone refresh my memory on what xmlns:oslc_disc=“http://open-services.net/xmlns/discovery/1.0/” is and when was it deprecated, please?

Sorry I should have been more careful with my vocabulary. I meant reify in generic sense not in an RDF sense.

I meant to formalize what we mean by and expect from links – and indeed we already doing this.

Re: We should reify the concept of link beyond just a single predicate

OSLC avoids and discourages the use of reification. It can make querying problematic, especially for OSLC query. I don’t think we should set a precedent just for this use case.

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.

Hi Eran,

Yes OSLC query for opt out makes sense, and it’s straight forward. we should discuss.

Ed,

Thanks for coming back to version 0…. Indeed this is what we should focus on and we rather call it version 1.

As I mentioned in my other note, IMO for Opt-out we should not recommend link index as this is too far from how Jazz behaves. I think we should recommend OSLC query. That also reduces the requirement to support TRS in that case. And again, there is the CCM anomaly that still relies on backlinking.

Regards,

eran

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.

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.

I do have one concern about Jim’s inverse link suggestion (though I generally think it’s a good idea).

Implementing inverse links is more significant implementation work for IBM ELM.

• All ELM tools need to understand that a “link” has inverse-labels and may also have inverse-links
• Tools will need to allow the creation of and query for both (filtering in the GC as appropriate

IBM ELM is still the 1000 ton gorilla in the OSLC space. Any new feature, as good as it might be, until implemented in IBM ELM is irrelevant in the real world.

This is why I much prefer the approach (which is compatible with above) that was suggested by the sodius team.  Tools should indicate in resource shapes for which links they query. In contrast to above, this is a very small step for IBM ELM – its just modified meta-data. It sets us up nicely for some of David’s suggestions below about further extensions to resource shapes.

Re: We should reify the concept of link beyond just a single predicate

OSLC avoids and discourages the use of reification. It can make querying problematic, especially for OSLC query. I don’t think we should set a precedent just for this use case.

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.

Re: We should reify the concept of link beyond just a single predicate

OSLC avoids and discourages the use of reification. It can make querying problematic, especially for OSLC query. I don’t think we should set a precedent just for this use case.

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.

As you suggest Jim, we could add a new property of an oslc:Property to indicate the reverse predicate for a link. This is not without its problems. Say we added a oslc:inversePropertyDefinition property. Consider the following use case (with imprecise Turtle):

Resource shape 1:

<prop1>
      a oslc:Property ;
      oslc:properyDefinition <forwardPredicate1> ;
     oslc:inversePropertyDefinition <reversePredicate1> ;
     ...

<prop2>
      a oslc:Property ;
      oslc:properyDefinition <forwardPredicate2> ;
     oslc:inversePropertyDefinition <reversePredicate1> ;

Resource shape 2:

<prop3>
      a oslc:Property ;
      oslc:properyDefinition <reversePredicate1> ;
     oslc:inversePropertyDefinition <forwardPredicate1> ;
     ...

Resource shape 3:

<prop4>
      a oslc:Property ;
      oslc:properyDefinition <reversePredicate1> ;
     oslc:inversePropertyDefinition <forwardPredicate2> ;
     ...

Now when you ask the question what is the inverse predicate for <reversePredicate1> across resource shapes, you get two solutions <forwardPredicate1> and <forwardPredicate2>. For reporting solutions that query for type system models in LQE (such as Report Builder) this doesn’t work.

This is a common pattern. You might use some predicate P1 for all link to some resource of type T1 regardless of the type of the subject resource. So there might be multiple resource types T2, T3, T4 that all use that predicate P1 to resources of type T1. However, the reverse predicate from type T2 to T1 is almost always different from type T3 to T1, and from type T4 to T1.

If you look at any single resource shape, it’s unambiguous.

I think we need to consider such a proposal carefully.

David.

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.