Cart
|
[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: XQuery types was Re: Yet another plea for XUpdat
 At 08:27 PM 5/4/2002 -0700, Dare Obasanjo wrote: >So I'll try to explain my point in lay terms. The main >benefit of a type system is so that things can be done >*statically* at compile time instead dynamically at >run time. Validation is a dynamic process. In other words, static typing means that you can find errors without testing them against data that exposes a particular error. The system tells you that there is a bug that would be exposed if you happened to run into the right data. This is a very good thing, because you don't always manage to construct tests that test everything in your code, and the data that will expose the problem may not exist yet. Validation, as you say, is a dynamic process, defined in terms of a schema and an instance. That's why you need structural subsumption, called the subtype relationship in our formal semantics. This is used to look at a query expression and the schema for a dataset and report whether there are any errors. The schema describes all possible instances that would validate. The type system of XQuery is based on structural subsumption for this reason. >Thus a "type system" based on validation isn't really >type system especially to people with a programming or >database background. True. Which is why we need the Formal Semantics, which is largely about structural subsumption. >Bottom Line: The XQuery type system although onerous >and complex does not forestall the need for >post-update validation if/when XQuery becomes a DML >and not just a query language. Therefore claims that a >"type system" is necessary before update semantics can >be added to XQuery are ill-considered. There *are* some things, like identity constraints and facets, that are not part of the static type system in XQuery. These things must be tested dynamically. Jonathan 
|
PURCHASE STYLUS STUDIO ONLINE TODAY!Purchasing Stylus Studio from our online shop is Easy, Secure and Value Priced! 
Download The World's Best XML IDE!Accelerate XML development with our award-winning XML IDE - Download a free trial today! Subscribe in XML format
|
|||||||||
