Re: c.d.theory glossary - RELATION

"mAsterdam" <mAsterdam_at_vrijdag.org> wrote in message news:40965d96$0$65124$e4fe514c_at_news.xs4all.nl...
> x wrote:
>
> > mAsterdam wrote:
>
> > We have some issues:
>
> Yes. I don't pretend I can solve them all, nor
> am I going to try in one blow. I would
> appreciate comments by others, I'll see how
> I can make something out of it for the glossary.
>
> Just some remarks for now.
>
> > RELATIONs vs. RELATIONSHIPs
> Namespaces to make some distance? I mean in this case:
> RM.RELATION vs. ER.RELATIONSHIP

I think we would do well to start with mathematical RELATION (which flows through many of these discussions) and then RM RELATIONSHIPS and ER RELATIONSHIPS. So, one primary def for RELATION and two candidate defs ;-) for RELATIONSHIP.

>
> > REPRESENTED vs. DESCRIBED
> > RELATION(SHIP)s vs RELATION(SHIP)s SET

I would think we could squeeze "relationship set" into the ER def of RELATIONSHIP and not make another entry for it in the glossary

> > FACT vs. THING (ENTITY)

It sounds like we should have ENTITY as an entry in the glossary -- maybe someone wants to start a thread for it?
.
> > First Order Logic vs. Higher Order Logic.
> Count me out. Help!
>
> > What is the equivalent of an ENTITY(SET) in the RM ?
> I don't think there can be equivalence.

I thought RM avoided the term "entity"

There is no
> possible representation for values in ER-modelling, no
> room for ENTITIES in RM. I do think a mapping is possible:
> An ER-graph can be like a roadmap to a relational database.
>
> Traditionally there can be Multivalued ATTRIBUTES
> in ER, RM has atomic ATTRIBUTES.
> So: RM.ATTRIBUTE and ER.ATRRIBUTE ?
>
>
> > Make sense to talk about ATTRIBUTES of a FACT ?
"attributes of a proposition" or "attributes of a predicate" -- I would think the later, with attribute values being part of a proposition.

> > How are those different from ATTRIBUTES of an ENTITY ?
As many have pointed out, the RM has more rigor than other branches or techniques, so one difference is that with RM attributes we should be able to get a tight mathematical def. When talking about attributes of an entity with ER or XML or elsewhere, the terms will be defined from a language & concept perspective, but not with mathematical rigor.

> > 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 ?

makes sense to me ;-) [but, of course, RM is loss-less decomposition, so ...]
--dawn

<snip> Received on Mon May 03 2004 - 17:55:31 CEST