XML Namespaces

We make a big deal out of the fact that XML describes data, not presentation information. But what good are data descriptions if you are the only one who describes a particular kind of data that way? XML allows authors to invent new element names and publish them for others to use and thus agree upon standard terms for common data elements. These published namespace s prevent name conflicts and indicate who defined a term. They also will make the work of search engines easier, as tags become more meaningful.

A name begins with a letter or one of a few punctuation characters, and continues with name characters, which include letters, digits, underscores, hyphens, colons, and periods. Names beginning with the string xml are reserved. Here's an example of some XM L that calls two defined data description namespaces -- one for an order, one for a digital signature (such as a VeriSign signature):

<xml>
<xml:schema>
<namespaceDcl href="http://www.company.com" name="co"/>
<namespaceDcl href="http://www.dsig.org" name="dsig"/>
</xml:schema>
<xml:data>
<ORDER>
<SOLD-TO>
<PERSON><LASTNAME>Layman</LASTNAME>
<FIRSTNAME>Andrew</FIRSTNAME>
</PERSON>
</SOLD-TO>
<SOLD-ON>19970317</SOLD-ON>
<dsig:DIGITAL-SIGNATURE>1234567890</dsig:DIGITAL-SIGNATURE>
<ORDER>
</xml:data>
</xml>

An author can also specify an element's data type and format. A lextype attribute can be used for this purpose:

<SOLD-ON lextype="DATE-ISO8061">19970317</SOLD-ON>

"DATE-ISO8061" specifies that SOLD-ON contains a date in the format specified by ISO 8061. Authors can design their own data types and use public types. Microsoft is working with the World Wide Web Consortium to define a set of standard types and will publish a list that anyone can freely use.