The data set may include information from a tax declaration form as well as information from the employee's hiring form, with both elements named Note - The default namespace is actually a specific namespace.
It is defined as the "namespace that has no name." So you cannot simply use one namespace as your default this week, and another namespace as the default later.
If the schema definition does not define a target namespace, then it applies to the default (unnamed, or null) namespace.
So, in our example, you would expect to see these target namespace declarations in the schemas: An array of Objects can be used only when the schema language has the ability to assemble a schema at runtime.
Finally, you cannot "back up" to an earlier part of the document, or rearrange it, any more than you can back up a serial data stream or rearrange characters you have read from that stream.
For those reasons, developers who are writing a user-oriented application that displays an XML document and possibly modifies it will want to use the DOM mechanism described in Chapter 3, Document Object Model.
It does not have any value to speak of (no name), but it is still precisely defined.
Again, the schemas can be declared either as part of the XML data set or in the program. In general, though, it is a good idea to keep all the declarations together in one place.) To declare the schemas to use for the preceding example in the data set, the XML code would look something like the following.
declaration consists of entry pairs, where the first entry in each pair is a fully qualified URI that specifies the namespace, and the second entry contains a full path or a relative path to the schema definition. In that way, only one copy of the schema will tend to exist.
(To learn more about XML Schema, you can review the online tutorial, XML Schema Part 0: Primer.
At the end of this section, you will also learn how to use an XML Schema definition to validate a document that contains elements from multiple namespaces.