XML Processing and Validation Merging Together
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Where does the border lie between validation and the processing itself? The question is if those should be even two separate procedures at all. Let's start with something simple like what the default values are. The most of the other Schema languages allow you to specify the default value. But when should the default value be used? What if some external resources are needed for the default value itself, like a database or a different value in the same document? Does the default value really have to be static? Yes that sounds familiar, it is processing already.
And what about the processing, didn't you ever need to be sure that the input is valid? And there is another common case, when you need to take actions during the processing based on the fact that some part of the document is valid or not. Sometimes you can't determine the variation of invalidness but you need to take some action based upon that.
XDefinition merging processing and validation
XDefinition is a schema language developed from the beginning with close respect to the natural readability by keeping the form of the XML data source. Designed to be understandable not only for programmers but also to analysts, system architects and all the other parties concerned with the project. This kind of approach leaves no space to misinterpret data description during it's exchange, starting from the architects to database specialists. XDefinition merges the validation and processing of the XML document as much as you need and what is more important if you need.
In the example below we show the usage of an external method, based on the information obtained during the validation is called method. An External method could be any static method in the class supplied to the XDefinition processor through it's API.
<?xml version="1.0" encoding="UTF-8"?>
<!-- addAuthor(String author) is user defined Java/.NET method in Autors class,
supplied to XDefinition thru processor's API -->
<Book title="required string"
author="required string(5,40); onTrue addAuthor(getText());"
If you find this kind of approach interesting read the article about readability of the schema languages here on the Javalobby called XSD Schema is not the only way or try the Tutorial with examples.
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