W3C home > Mailing lists > Public > public-vocabs@w3.org > March 2014

How to avoid that collections "break" relationships

From: Markus Lanthaler <markus.lanthaler@gmx.net>
Date: Mon, 24 Mar 2014 16:24:05 +0100
To: <public-hydra@w3.org>, <public-lod@w3.org>, "'W3C Web Schemas Task Force'" <public-vocabs@w3.org>
Message-ID: <018401cf4775$1a18eaa0$4e4abfe0$@lanthaler@gmx.net>
Hi all,

We have an interesting discussion in the Hydra W3C Community Group [1]
regarding collections and would like to hear more opinions and ideas. I'm
sure this is an issue a lot of Linked Data applications face in practice.

Let's assume we want to build a Web API that exposes information about
persons and their friends. Using schema.org, your data would look somewhat
like this:

  </markus> a schema:Person ;
            schema:knows </alice> ;
            ...
            schema:knows </zorro> .

All this information would be available in the document at /markus (please
let's not talk about hash URLs etc. here, ok?). Depending on the number of
friends, the document however may grow too large. Web APIs typically solve
that by introducing an intermediary (paged) resource such as
/markus/friends/. In Schema.org we have ItemList to do so:

  </markus> a schema:Person ;
            schema:knows </markus/friends/> .

  </markus/friends/> a schema:ItemList ;
            schema:itemListElement </alice> ;
            ...
            schema: itemListElement </zorro> .

This works, but has two problems:
  1) it breaks the /markus --[knows]--> /alice relationship
  2) it says that /markus --[knows]--> /markus/friends

While 1) can easily be fixed, 2) is much trickier--especially if we consider
cases that don't use schema.org with its "weak semantics" but a vocabulary
that uses rdfs:range, such as FOAF. In that case, the statement

  </markus> foaf:knows </markus/friends/> .

and the fact that

  foaf:knows rdfs:range foaf:Person .

would yield to the "wrong" inference that /markus/friends is a foaf:Person.

How do you deal with such cases?

How is schema.org intended to be used in cases like these? Is the above use
of ItemList sensible or is this something that should better be avoided?


Thanks,
Markus


P.S.: I'm aware of how LDP handles this issue, but, while I generally like
the approach it takes, I don't like that fact that it imposes a specific
interaction model.


[1] http://bit.ly/HydraCG



--
Markus Lanthaler
@markuslanthaler
Received on Monday, 24 March 2014 15:24:44 UTC

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