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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] RE: Are people really using Identity constraints specif ied in
 Len, Why have the schema muck with this stuff at all? If you are going to have to use another layer to do the validation - why separate out part of it and delegate it elsewhere? And especially if you create registries of definitions that are referenced by the transactions - then it becomes moot - since the registry provides you the ability to manage the rules and propagate changes. That's the rub. Hard wiring in local contraints usually comes back to haunt you - even if you think what you are hardwiring is unlikely to ever change.... Cheers, DW ============================================================= Quoting "Bullard, Claude L (Len)" <len.bullard@i...>: > John Sowa posted the following to the CG list. > Not surprisingly, I disagree with the conclusion > in this situation, but I do agree with the > rest of the text: > > "The basic point of the paper is the following > restriction: "all quantifications are bounded > by some variables". This kind of restriction > is very common for most practical applications. > > For database queries and constraints, an even > stronger restriction holds: every quantifier is > bounded by a *constant*, namely the cardinality > (number of rows) of the corresponding table. > > In natural languages, it is extremely rare to > find any sentence with an unrestricted quantifier. > Even when the word "everything" is used, some > implicit domain is almost always intended. > Furthermore, those domains are almost always > finite. (The major exceptions are books, papers, > and courses on mathematics.) > > In logic, a noun phrase such as "every employee" > maps to a typed, sorted, or restricted quantifier > of the form (Ax:Employee). Those quantifiers > usually have a constant upper bound, although > that bound may be very large for the domains > of people, bacteria, or web pages. > > This means that for most practical applications, > theories stated in first-order logic with restricted > quantifiers are decidable. However, the domains > might be so large that even a polynomial amount > of time is beyond the age of the universe. > > Bottom line: The most important issue is > scalability, not decidability." > > > From: Roger L. Costello [mailto:costello@m...] > > Hi Folks, > > Here are some thoughts: > > 1. Constraints on data are not equal to business rules. > > 2. Business rules change. Constraints on data do not. > > 3. Constraints on data should be specified in XML Schemas. Business rules > should not. Business rules should be specified in higher level application > code. > > Example: > > A company has employees. The current company policy on the minimum age > requirement is 16. Should the company create an XML Schema that constrains > <minimum-age> to 16? Or, should the company create an XML Schema that > simply constrains <minimum-age> to an integer, and let applications higher > up provide further constraints? > > Answers: > > - Mandating that the minimum age of an employee be 16 is a business rule. > It is highly likely to change over time. > > - The value of the <minimum-age> must be an integer. This is a constraint > on the data. It will not change over time. > > Therefore, an XML Schema should simply constrain <minimum-age> to be an > integer. Higher level applications should implement the business rule that > <minimum-age> be further constrained to 16. > > Comments? > > How would you characterize the distinction between "business rules" and > "constraints on data"? /Roger > > ----------------------------------------------------------------- > The xml-dev list is sponsored by XML.org <http://www.xml.org>, an > initiative of OASIS <http://www.oasis-open.org> > > The list archives are at http://lists.xml.org/archives/xml-dev/ > > To subscribe or unsubscribe from this list use the subscription > manager: <http://www.oasis-open.org/mlmanage/index.php> > > 
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