> -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf > Of baffled > Sent: Sunday, July 04, 2010 4:43 AM > To: jBASE > Subject: Re: how to create STUDENT database > > Jim > > I agree with you that having positionally-dependent multivalues is > often a poor design, but what exactly is wrong with having multivalued > phone numbers with an associated phone type? Surely that's an > appropriate use of an NR model and why WHEN clauses were invented.
As I said, if there is no implied order, such that MV #2 is always expected to be HOME and #3 WORK etc, then there isn't anything inherently wrong with that. But, if there are only 3 types, why would you want to complicate things by using output limiting clauses and string comparisons? With millions of records that would be a lot of overhead. Also, when you want to change the HOME number then you have to find it in the list first. So phone numbers tend not to be good examples after all unless you have lots of them and do not know what their name tags are in advance, in which case you would use a model something like that. > It's no different from how you would store it in a relational format, > with the benefits of the loss of the extra table and foreign key > columns (and the indexing and obvious join and transaction > overheads...) But most relational databases will optimize the heck out the storage for such a related table and the overhead isn't what it used to be. > > But there is a more general point: I've never come across a good > publication or course that taught how to design a multivalue database. > Plenty on how to code one up, administer one, use the various > languages etc. but nothing that dealt with the first principles of > design. Perhaps it's the assumption that everyone in the field is > migrating from some previous multivalue incarnation or working on some > kind of legacy application.. but they all seem to assume that you want > to build a house without laying the foundations. I don't think it has ever really been written up properly (but then, I would not have read much of other people's literature on the subject to be honest. Jim -- Please read the posting guidelines at: http://groups.google.com/group/jBASE/web/Posting%20Guidelines IMPORTANT: Type T24: at the start of the subject line for questions specific to Globus/T24 To post, send email to [email protected] To unsubscribe, send email to [email protected] For more options, visit this group at http://groups.google.com/group/jBASE?hl=en
