Re: c.d.theory glossary - RELATION

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"mAsterdam" <mAsterdam_at_vrijdag.org> wrote in message news:40929c58$0$36169$e4fe514c_at_news.xs4all.nl...

> > Sorry. The text at:
> > http://www.cs.sfu.ca/CC/354/zaiane/material/notes/Chapter2/node1.html
> > made a distinction between:
> > - ENTITY and ENTITY SETs
> > - RELATIONSHIP and RELATIONSHIP SETs
>
> A rephrase in their terminology would be:
> "ER-modelling has no way of representing an individual
> ENTITY, it only represents ENTITY SETs."
> But now I'am back where we started, because this would be a
> statement *within* ER-modeling.

We have some issues:
RELATIONs vs. RELATIONSHIPs
REPRESENTED vs. DESCRIBED
RELATION(SHIP)s vs RELATION(SHIP)s SET
FACT vs. THING (ENTITY).
First Order Logic vs. Higher Order Logic. What is the equivalent of an ENTITY(SET) in the RM ? Make sense to talk about ATTRIBUTES of a FACT ? How are those different from ATTRIBUTES of an ENTITY ? In ER modeling, a RELATIONSHIP is defined over ENTITIES: "A relationship is an association between several entities." In RM, a RELATIONSHIP is defined over VALUEs. What difference is between ENTITIES and VALUEs ?

> At the same site there is
> http://www.cs.sfu.ca/CC/354/zaiane/material/notes/Chapter2/node10.html,
> on how to get from ER to RM. They call it 'reducing' an
> ER-model to a relational model, which is BTW qualified as a
> 'record oriented' approach (I guess they needed something
> as opposed to object oriented). I don't see how this 'reduces'.
> More like 'expands', no?

Maybe they called it 'reducing' because some semantic information is lost by doing the translation ?

They don't talk about 'records' in the process of 'reducing'. They talk only about 'tables'.

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