David Cressey wrote:
> "Bob Badour" <bbadour_at_pei.sympatico.ca> wrote in message
> news:47558e4d$0$5265$9a566e8b_at_news.aliant.net...
>
>>David Cressey wrote:
>>
>>>"Jon Heggland" <jon.heggland_at_ntnu.no> wrote in message
>>>news:fj1iog$vcc$1_at_orkan.itea.ntnu.no...
>>>
>>>
>>>>Quoth David Cressey:
>>>>
>>>>
>>>>>I don't think of "formal" as a code word for "scientific". In fact, I
>>>>>don't even think "engineering" is code for "scientific". Science is
>>>
>>>about
>>>
>>>
>>>>>discovery. Engineering is about invention. There is a lot of overlap
>
> in
>
>>>the
>>>
>>>
>>>>>language, the tools, the method and the mode of thought. But they
>>>
>>>aren't
>>>
>>>
>>>>>interchageable.
>>>>
>>>>Yes, I was being sloppy. My (poor) defense is that the Norwegian word
>>>>for science ("vitenskap") is used rather more broadly than the English
>>>
>>>term.
>>>
>>>No problem. If I look up "ciencia" in a Spanish-English dictionary,
>
> the
>
>>>first meaning given is "science". But the second meaning given is
>>>"knowledge". That meaning is still in widespread use. I suspect that,
>
> not
>
>>>too long ago, the same would have been true in English.
>>>
>>>
>>>
>>>
>>>>>And I'll accept that information systems evolve along with changing
>>>>>requirements. But
>>>>>I'll also claim that some good analysis can accomplish in weeks when
>>>
>>>take
>>>
>>>
>>>>>months worth of iterative development.
>>>>
>>>>Yes, but despite my nifty definition, I still have a hard time
>>>>separating analysis and design/development. I find it very difficult to
>>>>imagine one without the other.
>>>
>>>I find it hard to imagine correct design/development without a correct
>>>understanding of the problem to be solved. Obtaining a correct
>>>understanding of the problem to be solved may be too informal a process
>
> for
>
>>>some people to give it a name like "analysis". Some people say they
>
> just
>
>>>sit down and chat with the users. But I think it's "analysis" whether
>
> it's
>
>>>a formal process or an informal one, and whether it's performed once at
>
> the
>
>>>outset of a project, or repeated between each iteration of an iterative
>>>development process.
>>>
>>>
>>>
>>>
>>>>>It would be interesting to know if there is a way of deriving relvars
>>>
>>>from
>>>
>>>
>>>>>some form of data analysis that doesn't involve ER. I am convinced
>
> that
>
>>>a
>>>
>>>
>>>>>set of relvars embeds design decisions, but I don't know from direct
>>>>>experience. What do you say?
>>>>
>>>>Well, what do you mean by "design decisions"? Relvars and constraints
>>>>(including, but not limited to, keys and foreign keys) represent
>>>>business rules. A specification of business rules seems like a natural
>>>>product of analysis to me. Of course, you could start with the business
>>>>rules and go to relvars from there.
>>>
>>>I agree. And a specification of all the business rules probably
>
> captures
>
>>>(at least) all the information recorded in an ER model.
>>>
>>>Now it's time for me to ak a dumb question:
>>>
>>>What is a relvar?
>>
>>A variable whose value is a relation.
>>
>>
>>
>>>How is it different from a relational table?
>>
>>SQL has tables. Relvars are relational variables -- either stored or
>>derived or automatic or global or local etc.
>>
>>
>>
>>>Is the difference mainly one of terminology?
>>
>>No.
>>
>>
>>
>>>or is there a subtle concept here that I need to learn?
>>
>>The differences between tables and relations are not all that subtle.
>>Relvar was introduced to disambiguate between relation values and
>
> variables.
>
>>
>>>What benefit was derived by introducing the term "relvar"?
>>
>>It avoids confusion when discussing relation variables versus relations
>>ie. relation values.
>>
>>
>>
>>>When was it introduced?
>>
>>Circa Third Manifesto
>>
>>
>>
>>>Are relvars designed?
>>
>>Yes.
>>
>>
>>
>>>Could there be more than one set of relvars derived from the same set of
>>>business rules?
>>
>>Yes.
>>
>
>
> Thanks for all these answers, Bob.
>
> Are tables not variables? If not, why not?
If you are talking about named tables in an SQL database, yes, those are
variables. Such a table is a variable as is a named view in an SQL
database. Each holds or associates with a table value.
Received on Tue Dec 04 2007 - 15:03:47 CST
