[topicmapmail] multiple Source Locators

[Lars Marius Garshol]

* Lars Marius Garshol
|
|  - topic maps support n-ary relationships

* Thomas B. Passin
| 
| Actually, so does rdf, de facto.

Oh, certainly. Maybe I should have expanded on the above and said that 

  - topic maps support n-ary relationships that are structurally
    identical to binary relationships

| If you let a node have a type like what we would call an association
| type, and hand a number of triples off that node, then it looks
| exactly like a topic map association, where the rdf predicates
| correspond to the topic map roles.

Yep. This is how my TM-to-RDF conversion works, described in the
"Living with RDF and Topic Maps". I *think* this is also what's in the
SWBP-WG proposal for modelling n-ary relationships in RDF, but that
drew criticism internally, precisely because it means having to
represent relationships of arity 2 and >2 differently.
 
| And of course in real like, you are likely to have this show up
| frequently.  For example, think of representing a row in a
| relational database.  You would have a node for the role, and a
| binary association hangind off the row node for each column entry.
| In relational database language, a row is termed a "relation", and
| that is just what it is.

Yep.
 
| The joke is that if you did this for a binary relationship (think of
| a 2-column table), you would in effect be reifying the relationship
| ("reifying" in the topic map sense"), but I have never seen this
| notion mentioned anywhere. 

One of the industrial track papers for ISWC '04 describes an ontology
that does this, because they wanted relationships to be "first class",
which, if I remember correctly, meant that they wanted to say things
about the relationships. IMHO they should have used topic maps.

| So rdf does has a way to provide for topic map-style reification
| after all, and it seems perfectly sensible to me. Of course,
| standard rdf processors wouldn't quite know what you were up to, but
| it would be legal and reasonable.

It would also be harder to query and different from non-reified
relationships. So it works in a pragmatic way, but is hardly perfect.

Anyway, you are absolutely right that RDF can support n-ary
relationships; I should have explained myself better.

-- 
Lars Marius Garshol, Ontopian         <URL: http://www.ontopia.net >
GSM: +47 98 21 55 50                  <URL: http://www.garshol.priv.no >