Re: General semantics
Date: Sat, 22 May 2010 21:31:56 +1000
Message-ID: <4bf7c0ad$0$14086$afc38c87_at_news.optusnet.com.au>
Erwin wrote:
> If that is so, then what useful purpose does it serve to invoke the
> name "subset constraint", if in the aftermath, it doesn't give any
> distinction anyway ?
> Inventing such names is, imo, creating complexity for the sake of it.
Well, I think we'll have to agree to differ here. My experience is that when you restate a domain expert's constraint in one of the standard forms, they're happy to have been understood and be able to confirm what they meant in a formal way. Comprehension and confirmation becomes a two-way street, and I've seen that with no other modelling process.
>> The point here is that while RM is the most precise and succinct way >> to represent a model, in order to develop correct models, it's easier >> to use tools that lend themselves to better communication with non- >> experts. That's what the field of fact-oriented modeling is on about.
>
> Then you agree with me that ORM is at the conceptual modeling level ?
> Then you must also agree that this has nothing to do with RM per se,
> and you must also agree that you contradicted yourself when you said
> "This stuff is pure relational"). ORM is an exercise in informality,
> whereas 'pure relational' is an exercise in formality.
No, I disagree. An ORM model can be incomplete (invalid) and yet have captured much of the conceptual content of a business problem. At the point at which the tools identify that none of ORMs metaconstraints are violated, it is a formal model; just as formal as a RM, and in fact directly expressible as RM, i.e., there's a one- -one correspondence for every expression (this is what Terry's thesis established, indirectly through the mapping to KL). I therefore claim that ORM is RM expressed in another language.
Now why is that useful? Because it enables the process of developing a complete model. When a business person says "Person works for Company", I can write *nothing* in RM, because I haven't yet decided what keys will be used for Person or Company, so I have no domains to form a tuple. Yet now that the fact type has been expressed, I can enter it into an ORM tool, which will accept it, but not give assent to the model as being valid until I define a identification schemes (key) for both.
Clifford Heath. Received on Sat May 22 2010 - 13:31:56 CEST