Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!snorkelwacker!bloom-beacon!eru!luth!sunic!tut!uta!csosnu
From: csosnu@uta.fi (Ossi Numminen)
Newsgroups: comp.software-eng
Subject: Re: CASE tools, esp. Software through Pictures.
Message-ID: <923@kielo.uta.fi>
Date: 13 Feb 90 07:33:51 GMT
References: <1990Feb6.215234.6561@is.uu.no> <1378@island.uu.net>
Reply-To: csosnu@kielo.UUCP (Ossi Numminen)
Organization: University of Tampere, Finland
Lines: 47

In article <1378@island.uu.net> dav@island.uu.net (David McClure) writes:
>We're using Software through Pictures (StP) for design of some internal 
>Personally, I find the Chen model both inadequate and misleading for design 
>of the information model, especially where many-to-many and non-binary
>relationships are concerned.  Until more advanced techniques are developed,
>I find a simple mapping of foreign key references and expansion of more
>complex relationships to be more helpful than Chen notation.
>

I also find Chen model inadequate in that version which is normally
supported by CASE tools.

One problem are participation/existence constraints. The ability to
represent these are missing in many CASE tools. Why not just to put these
two together and mark the cardinalities from 0 to n. This notation
is also more general that cardinalities marked from 1 to n with
participation constraints marked as T or P. At least IEW handles this
nicely.

Why can't you find weak entity types in ER editors in CASE-tools?
They are useful in many cases. The implementation of this facility
should definitely be not a problem.

I also wonder, why specialization/generalization hierarchies are
not implemented in ER editors in todays CASE tools? they are
extremely useful in every day modelling situations. It's true
that the graphical notation of these extended capabilities are
not commonly agreed, but the missing of them still bothers me.

In some CASE tools you can use recursive relationships (entity
types having a relationship to itself) but the situation could
be better. Without this facility, how do you model BOM-structures
or organization hierarchies in basic ER model in such a way
that the idea is conceptually clear in the first look?

>I would like to start a thread on these last two topics in comp.databases
>if I can get enough feedback.  Please post any ideas you have about extended
>ER models and levelling/consistency checking in DFD editors, or any other
>topics you feel are relevant.  Perhaps if we can reach some sort of
>consensus from the user-community on what is needed, the vendor-community
>could be inspired to respond (but I won't hold my breath)...
>-- 
>David McClure

 I'm looking very forward to the coming discussions.

Ossi Numminen