[Xesam] Link-by-id documentation and ontology patching

[Evgeny Egorochkin]

В сообщении от Friday 09 January 2009 23:08:58 Mikkel Kamstrup Erlandsen 
написал(а):
> 2009/1/9 Evgeny Egorochkin <phreedom.stdin at gmail.com>
>
> > I should have written this a bit earlier.
> >
> > http://xesam.org/main/Hackfest2008/Ontology mentions link-by-id
> > refinement. It
> > wasn't voted on or discussed widely though, so let's do it now...
> >
> > The idea is to treat content authorship as a special case and
> > refine "dangling" link representation:
>
> I must admit that I am having some problems parsing your message, so I'll
> riposte with some questions :-)
>
> First: Are we talking xesam:creator only here or are we discussing a more
> general idea?

xesam:creator is more or less treated as an exception or as a properly typed 
version of original link-by-id
>
> 1) xesam:creator chilren are allowed to only link to xesam:ContactMedium of
>
> > xesam:Contact, which is consistent with the way it's usually done in RDF
> > world.
> >
> > 2) Links by ID between documents are resolved directly to URI of the
> > document(s) if it exists, or a dummy Document of appropriate type is
> > created
> > with ID assigned to it and xesam:Source set to xesam:Unavailable.
> >
> > Examples:
> > 1)      BookA references ISBN:xxx and there's a BookB with ISBN:xxx ==>
> >                user:BookA              xesam:links             user:BookB
> > 2)      BookA references ISBN:xxx and there's no document with ISBN:xxx
> > ==> user:BookA                      xesam:links
> > user:DummyBookB.
> >                user:DummyBookB rdf:type                xesam:Document;
> >                                                rdf:type
> >  xesam:Unavailable; # or maybe don't specify Source
> >                                                xesam:isbn
> >  "xxx".
> >        if BookB with ISBN:xxx appears, (2) is replaced with (1)
> >
> > pros:
> > * no need to turn all IDs into URIs
>
> We still want globally unique IDs, no? I can't see how that is possible
> without URI schemes

Yes, ID field values won't be globally unique then. Only values of a 
particular field stay unique. 

> * direct links work much faster
>
> What do you mean direct link? You link to BookB via its URI user:BookB just
> like one would use any other id...

You'd have to have an index for every id field for this to work fast enough 
and still you have several times more uris to match. Of course the 
performance penalty greatly depends on the rdf/sql backend.

> * better handing of dangling links:
> >        - links to available and unavailable objects "look" the same to
> > applications
> >        - dummy objects can have an appropriate type like Document or
> > Media and be
> > properly displayed
>
> As far as I can see the model described in the wiki can handle what you
> describe just fine..?

Indeed, you can create dummy objects when you use link-by-id... my bad, but a 
good idea nevertheless :)

> * documents can't be authored by audio files
>
>
> This is a bit academic, but true.

Not too academic though since you can expect to confront software with 
metadata it's not fully aware of with the only available description being an 
ontology.

> cons:
> > * reason for linking isn't specified when both objects are available.
> > This doesn't seem to matter to users for links by ISBN and such.
> > * if there are 2 documents with the same ISBN(eg PDF and ODF versions), a
> > link
> > by ISBN would target both of them. However, to properly link the second
> > document, the reason for linking(ISBN reference) must still somehow be
> > available
> > * xesam:creator sort of feels like a createdBy relation
>
> I must admit that I am pretty lost here... I this all about making
> xesam:creator a relation-but-not-quite?

More like dropping link-by-id for everything but creator :)

-- Evgeny