- From: Frank Manola <fmanola@acm.org>
- Date: Fri, 12 Aug 2005 11:09:32 -0400
- To: Natasha Noy <noy@SMI.Stanford.EDU>
- CC: Guus Schreiber <schreiber@cs.vu.nl>, "Ralph R. Swick" <swick@w3.org>, swbp <public-swbp-wg@w3.org>
Natasha Noy wrote: > > Guus, > > Thank you very much for your comments. Some replies/discussion below. I > think some points require a bit more discussion (there maybe some > misunderstanding). > snip >> >> Again, examples 3 is the prototypical n-ary relation, so maybe this >> should be the first example. The point is that for people from >> relational databases the first two examples are not "real" n-ary >> relations: e.g. in example 1 the probability value is functionally >> dependent on the person and the disease. In example 3 there is no such >> dependency (the primary key is the combination of all three >> arguments). So, reification would work with examples 1 and 2, but not >> with example 3 (because the instances are not unique). > A small terminology quibble: As long as the first two examples can be expressed as n-ary relations in a relational database (which they can), they can be considered "real" n-ary relations even to people from relational databases. I think what you have in mind is that the resulting n-ary relations would not necessarily be in some normal form that eliminates specific dependencies (having to do with the semantics) that may exist, and hence that relational database designers would probably not represent these as single n-ary relations. But it's still possible (and people certainly design "unnormalized" relational schemas). --Frank
Received on Friday, 12 August 2005 15:06:53 UTC