[topicmapmail] binary associatinons: Two roleSpecs or many more?

[Johannes Busse]

Hello XTM discussion list,


in defining an ontology I got the following
question: I am wondering, how many roleSpecs can (or
should be) "attached" to an association with *two*
members: Two roleSpecs or many more?


In some example-XTM I have looked at there are
always the same roleSpec attached to the members
of an association. Example:

<association>

  <instanceOf> 
      <topicRef      xlink:href="authorship" />
  </instanceOf>

  <member>           <!-- first member -->
      <roleSpec> 
          <topicRef  xlink:href="author"/>
      </roleSpec>
      <topicRef      xlink:href="Shakespeare"/>
  </member>

  <member>           <!-- second member -->
      <roleSpec> 
          <topicRef  xlink:href="work"/>
      </roleSpec>
      <topicRef      xlink:href="Hamlet"/>
  </member>

</association>


Once we know the type of an association (here:
authorship) we also know the roleSpecs of the
"first" and "second" assoc-member. The whole
semantic information is included in the
assoc-name. 

It seems to me that this often is a reminiscence to the
database-notion of an relation, where the
table headings are semantically not very interesting.

In XTM on the other side it enhances the "semantic
densness" if we attach many different roles to one
association type. In  the above example we could
exchange "author" with "editor", "publisher",
"referee", "web publisher" etc. Or we can exchange
"work" with more specific sorts of text. 

The ontology impregnated within the XMT-model for
me seems to be semantically mor rich than the
ontology of relational modeling. The nature of a
link between two topics consists always of three
elements: assoc, "left" role, "right" role.


My question to you: is that right? 


Iff this is right, there are several consequences:

(1) The topic-view of an XTM-Browser should show
not only associated topics, but also the attached
roles *for each topic*. (To my knowledge eg. the
omnigator does this not. Is this a feature or a
lack of function?) - Do you know, where this
slightly complex problem of visualisation is
solved?

(2) the notion of transitivity of associations
must keep in mind also the roleSpecs. 

(3) an association can be seen as a "sparse"
relation: 
- each row has indefinitely many columns, which
- most of them are empty or "undefined", whereby
- only very few of them are  used
- these which are used have to be made explicit by
  means of the roleSpec

?

thank you
Johannes Busse

(XTM-newby, 3 month experience :-)


--
Dr. Johannes Busse,  Erziehungswiss. Seminar,  Univ.Heidelberg
Akademiestr.3, 69117 HD  |  Kellereigasse 3, 69 526 Ladenburg  
tel 06221 / 54-7531      |  tel 06203 / 95 35 83
http://www.jbusse.de        mailto:busse@ews.uni-heidelberg.de