Cart
|
[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Re: Strong versus (weak|runtime) typing
 There's been surprisingly little discussion of Sean's original question: >Is the strong/weak/runtime typing argument over XML any different from >that debate in programming languages. I do think that this argument is different for XML. In programming languages, it is rare to argue whether integers should be allowed to exist in data, or whether the serialization should be considered the true form of the data. Most programming languages that allow complex structures also have fairly strong typing - though it may well be runtime typing rather than static typing. Personally, I believe that XML documents contain a wide range of type information, from very loosely typed information without even a DTD, to rigidly structured data corresponding to relational data or objects. A language designed for processing XML needs to be able to deal with this fact gracefully, avoid imposing assumptions on what is allowed that conflict with what is actually found in the data, allow data to be managed without turning explicit casts into a common idiom, and allow the programmer to focus on the documents being processed and the task to be performed rather than the quirks of the type system. Some people seem to feel that only weakly typed systems meet those requirements. I disagree. I think that a language whose type system matches exactly the types found in XML documents will be most graceful for processing XML. If the XML is governed only by a DTD or has no schema, the appropriate types are document, element, attribute, node, text node, processing instruction, comment, ID, IDREF, IDREFS, etc. A strongly typed language that does not support these types tends to get in the way, because it is a poor match for the data being processed. It insists on the wrong things. If W3C XML Schema is used, then documents can also contain the kinds of types typically found in strongly typed programming languages, plus some types typically not found anywhere. Again, the most graceful type system for a programming language is the one that best matches the data being processed. And even in this case, the type system must be very flexible, because the output types may be quite different from the input types. Strong typing is not synonymous with needing to write the names of types everywhere and do lots of explicit casts, though this is common in many strongly typed languages. Implicit typing allows a programming language to infer a type, assigning the correct type to a variable without requiring the programmer to write down the name of the type. The ideal is to come up with a type system that catches errors early without imposing too much overhead on programmers. This is difficult and subtle, and you have to both look at it theoretically and by looking at lots and lots of examples. But I think that XML has become important enough to deserve such a type system. 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
|
|||||||||
