Summary

This chapter covered a lot of ground. Some of the specifications discussed are completed and others are still works in progress. The five primary categories discussed were advanced markup, namespaces, XLink, XPointer, and XML Schemas.

The advanced markup section covered all the areas of the XML 1.0 specification left out in Chapter 1. Here is a brief description of the topics covered in this section:

• Character references enable you to represent any Unicode character in your XML document.

• Entities allow you to abbreviate some replacement data and refer to that data via an entity reference. There are several categories of references to include general, parameter, internal, external, parsed, and unparsed.

• All attributes are typed in order to constrain the values that may be assigned to them. The legal attribute types (in a DTD) are CDATA, Enumeration, NOTATION, ID, IDREF, IDREFS, ENTITY, ENTITIES, NMTOKEN, and NMTOKENS.

• Attribute values are normalized before being passed on to the processing application.

• The xml:space attribute can be attached to any element to determine how whitespace should be handled.

• Element content specifications describe how subelements may be nested. We discussed the ANY and mixed content models.

• CDATA sections allow you to pass raw text (even XML) on to your processing application without it being treated as XML.

• A processing instruction may be used to pass additional information on to one specific application.

• The standalone document declaration is used to signify whether the XML processor is required to fetch the DTD.

Namespaces are a W3C recommendation to create element and attribute names that are globally unique. A unique name is created by separating an XML name into two parts: a prefix and a local part. The prefix is further mapped to a URI.

The XLink specification defines how to create links in XML documents. Links are created via attributes in the XLink namespace. XLink defines two types of links: simple and extended.

The XPointer and XPath specifications define a syntax to refer to a specific element or set of elements inside of an XML document. XPointers use location path expressions. A location path is a series of location steps separated by a /.

XML Schemas define a new syntax for describing the structure and datatypes of a class of XML documents. Unlike DTDs, XML Schemas are a markup language that conforms to XML syntax. XML Schemas also have a larger set of built-in datatypes than DTDs to include float, int, date, and uriReference.