XML Hacks

Choose Tools for Creating an XML Vocabulary

XML provides the syntax necessary to create your own vocabulary or dialect of XML. Here are a few things you need to know about namespaces and schemas.

One of the best things about XML is that you can create your own tags—a vocabulary or dialect—if you want. To create a vocabulary, you should understand a couple of things about schemas and namespaces. You can use XML without schemas or namespaces, but sometimes you want to use one, the other, or both. This hack explains when you’ll want to use schemas and namespaces and when you’ll want to avoid them.

Well-Formedness, Validation, and Schemas

XML documents must be well-formed. This means that they must adhere to the syntax defined in the XML specification (http://www.w3.org/TR/REC-xml/). This syntax mandates such things as matching case in tag names, matching quotes around attribute values, restrictions on what Unicode characters may be used, and so on.

An XML document may also be valid. This means that such a document must conform to the restrictions laid out in an associated schema. Basically, a schema declares or defines what elements and attributes are allowed in a valid instance, including in what order the elements may appear. Governing document layout with schemas can greatly increase the reliability, consistency, and accuracy of exchanged documents.

DTD

The native schema language of XML is the document type definition or DTD [Hack #68] , which is part of the XML specification ...