Thorsten Ottosen wrote:
Daniel Walker wrote:
On 4/23/06, Thorsten Ottosen <thorsten.ottosen@dezide.com> wrote:
Schemas give you data types and type checking, which obviously is nice to have when you're dealing with data. I think XML schema validation is one of the most import features of XML for the same reason that I like C++ templates and type-safe compile time polymorphism: making sure your data types are correct before hand gives you one less thing to worry about.
Why is that better than a run-time exception when loading the file?
Why is what better? Maybe I wasn't clear. When an XML file includes a schema and fails validation when loaded, you do get a run-time exception. I was trying to say that's a good thing. An XML validating parser is similar to a compiler for a strongly typed language: it catches type errors (in addition to syntax errors) immediately before you actually try to use the file.
Ok, why is that exception better than the one I generate if I don't meet the tag I expect, of if the contents of a tag is not of the type I expect?
-Thorsten _______________________________________________ Unsubscribe & other changes: http://lists.boost.org/mailman/listinfo.cgi/boost
It's not that the exception is atomically better, but the question seems similar to the old-time 2-phase construction programmer asking why it's better to avoid 2-phase construction. The parsing/validation of XML allows me to trust that my data structure has been constructed fully and as a valid foo - or that an exception was thrown for some appropriate reason. For XML, malformed XML itself is akin to a constructor call where it can only be determined to be malformed at runtime. In fact, in each of the places where I've used XML to transmit data , it has been a representation of an invariant. This is no different than a class which properly represents an invariant, and I prefer not to be able to receive broken objects from factories. Pardon me if I'm missing the point of your question... Brian Allison