Re: [Crm-sig] URI Management [Issue 460]

Tue, 28 Sep 2021 09:25:18 -0700

All

I do not think it is good practice to limit access to deprecated resources by intercepting requests. A general coded response may trigger an exception in a consuming application, but no appropriate action can be taken until the specific reason is known. In the case of deprecation, appropriate action might include replacing the deprecated resource in the local application, removing the deprecated resource, or leaving it untouched (in which case the application remains out of synch with the CRM - but that is their choice).

I think it is better to return deprecated resources on request, but clearly mark them as deprecated. A consuming application can set up an exception when the mark is encountered (or not, if synchronization is not an issue).

I don't think there is any commonly-agreed method of marking the status of resources. For what it's worth, the RDA Registry uses a local status property and coded value (see http://www.rdaregistry.info/rgAbout/updates/deprecation.html).

Redirection to a 'better' or replacement non-deprecated resource can be handled by publishing a mapping from the deprecated resource. Again, this is more flexible for consuming applications, and is also easier to maintain and manage. Human redirection can be handled by a comment attached to the resource.
On 27/09/2021 15:29 Ethan Gruber via Crm-sig <crm-sig@ics.forth.gr> wrote:


What about 410 Gone:

"Indicates that the resource requested is no longer available and will not be available again. This should be used when a resource has been intentionally removed and the resource should be purged. Upon receiving a 410 status code, the client should not request the resource in the future. Clients such as search engines should remove the resource from their indices.[42] Most use cases do not require clients and search engines to purge the resource, and a "404 Not Found" may be used instead."

So if you request a deprecated property/class with content negotiation for application/rdf+xml, the response you get tells you it no longer exists. I think the semantics of 410 are more clear than 404.

There are probably multiple scenarios for redirections.

Deprecated and replaced with a single new URI: 303 See Other
Deprecated and replaced with more than one URI: 300 Multiple Choices (in this case, you can use the Link HTTP header to provide multiple links, but the user will have to make a choice).
Deprecated and not replaced at all: 404 or 410.

We have similar scenarios in dealing with new editions of Roman coin typologies. A new volume might have decided that one typology from an old volume is now actually two typologies. So we implemented 300 Multiple Choices when people request the URI from the old volume. Otherwise, in 1:1 relations between the old and new volume, it's a 303.

Ethan

On Mon, Sep 27, 2021 at 10:11 AM Pavlos Fafalios <fafal...@ics.forth.gr> wrote:
Thank you Ethan. 

Redirecting to Migration Instructions for a deprecated class seems reasonable when the request is of type HTML. However, I think this is impossible when the request type is RDF/XML; we either point to 404 or (?) redirect to some other class, e.g., the one mentioned in the migration instructions (e.g., using 303). Not sure if the latter is a good option (it also does not seem straightforward to implement in some cases, e.g. for P88, P115 and others).

Best,
Pavlos 

On Mon, Sep 27, 2021 at 4:55 PM Ethan Gruber <ewg4x...@gmail.com> wrote:
I agree with Rob.

In the case of Part D, I suggest the HTTP 303 See Other for a replacement/renaming. I agree there shouldn't be a 404 for a deprecation, but there should be a 3xx code for redirecting to the Migration Instructions. 301? Not sure.

On Mon, Sep 27, 2021 at 9:40 AM Robert Sanderson via Crm-sig <crm-sig@ics.forth.gr> wrote:

Reordering to most important first..

(C) BASE URI (NAMESPACE) FOR CLASSES AND PROPERTIES 
What base URI should we use for the classes and properties of each version when serving RDF content? There are three options:
Option B1. Always use an unversioned base URI, i.e., http://www.cidoc-crm.org/cidoc-crm/ for all ontology versions. 


This is the correct answer, according to 2 decades of RDF / Semantic Web  experience.
In particular, FOAF, one of the earliest RDF ontologies and written by one of the original authors for RDF Dan Brickley, warns us in the specification:

Much of FOAF now is considered stable. Each release of this specification document has an incrementally increased version number, even while the technical namespace ID remains fixed and includes the original value of "0.1". It long ago became impractical to update the namespace URI without causing huge disruption to both producers and consumers of FOAF data. We are left with the digits "0.1" in our URI. This stands as a warning to all those who might embed metadata in their vocabulary identifiers.
(emphasis added). http://xmlns.com/foaf/spec/ 

Please, do NOT put a version number into the URIs. It makes everyone's lives worse, and breaks interoperability between systems. It also makes it much harder for people to upgrade systems and retract/republish data, meaning we will leave folks behind in previous versions. It also makes it harder to aggregate data, as the same property (say, P2) has different URIs in different systems.

I would go so far as to say that, given we already have different RDFS and OWL namespaces, that if there was further fragmentation, it would further harm adoption and most users would simply pick the one that was easiest for them given the already incompatible URIs. 

In looking at similar topics (XML namespaces, API versions) the results are the same -- URIs should be persistent, and versions / dates make them either less persistent or appear out of date, both of which are harmful.

Thanasis has already made a point about not using versioned base URI:
"I am suggesting that classes do not need versions at all. Doing reasoning on a per class and per version basis would be bad practice, no? One would expect that the whole RDF/OWL representation would be used for reasoning. I think class URIs are only used as identifiers. This also avoids the problem of ensuring correct older versions for deprecated classes."
Thanasi, could you please elaborate more on this? It's not clear to us why/how reasoning considering a particular ontology version is affected when versioned URIs are used for the classes and properties.

As above, but Thansis is 100% correct - URIs are used as identifiers. We wouldn't change the numbers in the ontology (E22, P2 etc) ... in RDF the URI has the same function.


On Mon, Sep 27, 2021 at 6:41 AM Pavlos Fafalios via Crm-sig <crm-sig@ics.forth.gr> wrote:
Dear all,

We (at FORTH) have started working on the URIs management issue, i.e. on how to provide resolvable URIs for the different versions of CIDOC-CRM and its compatible models. We would like to hear you opinion about the following: 

(A) HAVING BOTH UNVERSIONED AND VERSIONED ONTOLOGY URIS  

The URI http://www.cidoc-crm.org/cidoc-crm/ will always resolve to the last official version of CIDOC-CRM ('official' according to the definition here). 
A question (also raised by George) is if we want to point to the last 'published' version (which is "a stable version of the standard and can be used for implementation, referencing and any other official purpose").

In parallel, each version will have its own versioned URI, e.g., 
http://cidoc-crm.org/cidoc-crm/6.2.9/ for version  6.2.9, etc. etc.

Yes. Best practice would be that the documentation for each version has a separate URI, and a common URI can be used to always refer to the latest version.

This is less important than (C) (people are better at concluding identity than machines!) but still important :)


(B) SERVING HTML OR RDF (BASED ON HTTP REQUEST TYPE)

Different content will be served based on the type of the HTTP request. So, if one asks for 
will get either the HTML content of the last official version (using text/html content type), 
or the RDFS of the last official version (using rdf/xml content type).  We will do the same for also the versioned URIs. 

Excellent.


Now, if one requests a specific class or property, e.g.: 
or (for the case of rdf/xml) will get the entire RDFS of the last official version OR the star-view of that particular class (i.e., subclasses, superclasses, incoming properties, outgoing properties). 

Star view, or just the term itself. You can always get the entire RDFS by going to the namespace.


(D) WHAT WE DO WITH RENAMED AND DEPRECATED CLASSES

1/ Renamed: When resolving a class/property (of a specific version) which has been renamed, we can point the user to the information about the renamed class (since semantics stay the same). For example:
users will get information about http://www.cidoc-crm.org/cidoc-crm/E78_Curated_Holding 
(once URI resolving has been implemented)

Yes, and ... via an HTTP redirect to the new name for the class/property please.


2/ Deprecated: When resolving a class/property (of a specific version) which has been deprecated, we (Pavlos and Elias) suggest not returning anything (404 response code).  In our opinion, this makes sense since the ontology version does not anymore contain the requested class/property. In the case of HTML content type, we can also point the user to the Migration Instructions (page 229). Any comments?

Yes, agreed.



(E) COMPATIBLE MODELS  

The plan is to follow the same approach for the compatible models. Here, it seems that having versioned URIs for the ontology and the extension models solves the problem of how to point to specific versions (as mentioned by Francesco). We just need to include the versioned namespaces of the considered models in the RDFS.

Yes, agreed.

Thanks!

Rob

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--
Dr. Pavlos Fafalios
Postdoctoral research fellow
Project ReKnow (MSCA Individual Fellowship) 

Centre for Cultural Informatics / Information Systems Laboratory
Institute of Computer Science (ICS)
Foundation for Research and Technology (FORTH)
   and
Visiting Lecturer
Department of Management Science & Technology (MST),
Hellenic Mediterranean University (HMU)

Address: N. Plastira 100, Vassilika Vouton, 70013 Heraklion, Greece
Email: fafal...@ics.forth.gr 
Tel: +30-2810-391619 
  
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Cheers

Gordon

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