Re: URIs and Unique IDs

See inline comments.

On Thu, Oct 30, 2008 at 4:20 PM, Michael Lang(Jr.) <
michaelallenlang@gmail.com> wrote:

> Michael,
>
> I'm not sure that its as cut and dry as:
>
> "Thus, any ontology versioning system of the future will rely on these two
> principles:
> 1. If the semantics of a term changes, then it needs to have a new unique
> ID.
> 2. If the semantics of a term does NOT change, then it should maintain the
> same ID in any future versions."
>
>
> There will certainly be times when an ontology-driven application is
> purposely dependent on the evolution of the semantics of a term.
>
>
 In other words, the application wants to change its behavior when the
> semantics of a term are changed.  In this case, the URI should not be
> changed if the semantics of a term are changed. If it was changed, the
> application would keep functioning in its original manner instead of
> adapting to the new meaning of the term.
>

Can you think of a clear example where the application will only do the
right thing when the unique identifier (UID) for a resource ceases to be
used for that [conceptual] resource and is instead used for a resource with
a different semantics?  In this case, do you propose that the application is
notified of the new meaning or, it just changes w/o notice? Note, I'm asking
about the UID in a world where it is de-conflated from the URI and the
physical location on the web.



> I think, in general, it should be left up to the community of users and/or
> managers of an ontology to communicate with each other and decide what
> approach to take when creating a new version of an ontology.  Different
> ontologies and different applications will require different approaches.
>

Proably true in general, but I need some concrete examples to be convinced
that willy nilly semantics changing of the semantics of resources is
desirable.


>
> Mike Lang
>
>
> On Thu, Oct 30, 2008 at 5:14 AM, Michael F Uschold <uschold@gmail.com>wrote:
>
>> I'm resending this message to the semantic web discussion group for the
>> record.
>>
>> On Wed, Oct 29, 2008 at 3:53 PM, Michael F Uschold <uschold@gmail.com>wrote:
>>
>>> Currently there is no accepted practice on how/whether to migrate to new
>>> URIs when a new version of an ontology is published. This is largely due to
>>> the fact that there is no good technology for managing versioning, and the
>>> W3C consciously (and probably sensibly) decided not to address the issue.
>>> Versioning information is meant to be placed on a version annotation.
>>>
>>> However the current situation is like the wild West, and everyone will be
>>> doing different things, resulting in a mess.
>>>
>>> Wordnet published a new version and minted all new URIs even though many
>>> or most of the entries were semantically identical.
>>> The SKOS working group is currently considering the pros and cons of
>>> various options. One is to adopt all new URIs in a new namespace, just like
>>> Wordnet. Another is to keep the exact same name space, and change the
>>> semantics of a small number of terms while keeping the same URI. A third is
>>> to keep the same URI for the unchanged terms, and mint new URIs for the
>>> terms with different semantics.
>>>
>>> This is a problem because they have no guidelines, they are basically
>>> stumbling along in the dark.
>>>
>>> I believe that this is an urgent matter that needs attention to prevent a
>>> nightmare from unfolding.
>>>
>>> In the current state of semantic web use, it may not matter to much what
>>> choice the SKOS team chooses. This is mainly relatively few applications
>>> will be impacted, which may be due to the fact that the applications are not
>>> driven by the ontologies.
>>>
>>> However, when usage of ontologies and ontology-driven applications
>>> becomes more mainstream, the differences could be profound. Given that this
>>> issue is intimately tied up with versioning, and that we have no good
>>> solutions yet, do we continue to throw our hands up and punt? Absolutely
>>> not, it is essential that a good precedent is set ASAP that is based on
>>> sound principles.
>>>
>>> Here is how.
>>>
>>> We should imagine a future where ontology versioning is handled properly
>>> and do things that are going to make things easy to migrate to that future.
>>> We don't know how the versioning black box will work, but we should be able
>>> to make some clear and definitive statements about WHAT it does.
>>>
>>> For example, in the future, ontology-driven applications will be fairly
>>> mainstream. URIs are used as unique identifiers. When applications are
>>> driven from ontologies, then they will break if you change the semantics in
>>> mid-stream.  Imagine an application that relied on the semantics of broader
>>> as it was originally specified with transitivity.  They loaded data that was
>>> created using that semantics. Then the SKOS spec changes and broader is no
>>> longer transitive. New datasets are created according to this new meaning.
>>> The application loads more data. It needs to know which data is subject to
>>> transitive closure and which is not. This is impossible, if the same SKOS
>>> URI is used for versions with different semantics.  They are different
>>> beasts, and thus MUST have different URIs.
>>>
>>> Similarly, if SKOS mints a whole new namespace and changes all the URIs,
>>> the application also has a problem. It has datasets with the old URI and
>>> datasets with the new URIs. This means that the datasets will not be linked
>>> like they should, they will treat the two different URIs for the same thing
>>> as being different.  If one wanted to go into OWL-Full, one can use
>>> owl:sameAs, but this is not very practical.  The only reasonable solution is
>>> to have the same URI for things with the same semantics.
>>>
>>> Thus, any ontology versioning systemof the future will rely on these two
>>> principles:
>>> 1. If the semantics of a term changes, then it needs to have a new unique
>>> ID.
>>> 2. If the semantics of a term does NOT change, then it should maintain
>>> the same ID in any future versions.
>>>
>>> If either of these two guidelines are broken, then so will the
>>> ontology-driven applications of the future.
>>>
>>> These maxims hold without exception for any standards that are formally
>>> released as standards.
>>> A question arises if we need to hold to the same standards for standards
>>> like SKOS which was never formally blessed.
>>>
>>> The practical difficulties will be the same whether the standard is
>>> blessed or not. It only really depends on whether the standard is a de facto
>>> standard,or whether it is getting significant use. If users build things and
>>> ontology producers break things through carelessness, this will hinder
>>> semantic web technology adoption.
>>>
>>> Another question is what to do if the original standard is belived to be
>>> incorrect, and the new one is the fixed one. Can one then keep the same URI?
>>> Again, the answer should be informed by the impact on applications. The
>>> same problems will occur if you change the semantics and keep the same URI
>>> even if you are fixing a mistake.  The URI with the wrong semantics must
>>> keep its original unique ID.
>>>
>>> Michael Uschold
>>>
>>
>>
>
>
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