Path: utzoo!yunexus!geac!daveb From: daveb@geac.UUCP (David Collier-Brown) Newsgroups: comp.databases Subject: Re: Informix 4GL Question? Summary: Parts 2 & 3 Keywords: Informix 4GL, SQL, Relational theory Message-ID: <2390@geac.UUCP> Date: 6 Mar 88 16:40:48 GMT Article-I.D.: geac.2390 Posted: Sun Mar 6 11:40:48 1988 References: <714@uel.uel.co.uk> <2314@geac.UUCP> <1169@ucsfcca.ucsf.edu> Reply-To: daveb@geac.UUCP (David Collier-Brown) Organization: The Geac Semantic Gap Department. Lines: 59 >In article <2314@geac.UUCP> daveb@geac.UUCP (David Collier-Brown) writes: >> This is interesting, in that it is a perfectly plausible request >>that does not **seem** to be well-defined in the relational >>algebra/calculus (and perhaps even less well-defined in the *#%!@?&& >>sublanguages we get with them). In article <1169@ucsfcca.ucsf.edu> brianc@daedalus.UUCP (Brian Colfer) writes: > Relational theory explicitly assumes that data is abstract and >therefore the sublanguages (SQL,etc.) should adhere to this assumption. >From E.F.Codd in Database programming and design vol. 1,no 2 (Feb. 88) [further clarification elided] >> 2) "give me the first n of" -- from a problem in bibliographic >> search >> 3) "give me any n of" > >Non-sensical from a relationship model perspective. That's what I was hoping to discover. Relational theory excludes significant consideration of certain uses of the data which it describes. And that is a prefectly reasonable thing for it to do: it is concerned with the nature and organization of data, not ad-hoc manipulations such as the ones I raised. This raises a semantic-gap problem, though, in that selected applications need operations which are not well-defined within the constraints of the theory. > Plus from a >application perspective to arbitrarialy select a set of row(s) because of >its position is illogical. Quite the contrary! In this case, one is doing bibliographic query on a very large database over a finite-speed link with limited display area for the results (lets assume bus speeds and a 1M*1M bit screen). Human inspection of an arbitrary subset, *traditionally* the first N encountered, is required to discover if the data requested is the data desired. Response is required to take less than a minute. Without a theory which accepts such illogical (:-) constraints as human, processing, communication and display limitations, one has two choices: 1) kludge it, or 2) improve the theory. I know how to do (1). Any suggestions on (2)? --dave c-b ps: As suggested in other postings, one can kludge this within SQL, with a wee bit of subtlety. -- David Collier-Brown. {mnetor yunexus utgpu}!geac!daveb Geac Computers International Inc., | Computer Science loses its 350 Steelcase Road,Markham, Ontario, | memory (if not its mind) CANADA, L3R 1B3 (416) 475-0525 x3279 | every 6 months.