IBM Version 5 manual

￿XML Schema Part 0: This is a primer, it is intended to provide an easily readable description of the XML Schema facilities, and is oriented towards quickly understanding how to create schemas using the XML Schema language.

￿XML Schema Part 1: Structures specify the XML Schema definition language, which offers facilities for describing the structure and constraining the contents of XML 1.0 documents, including those which exploit the XML Namespace facility.

￿XML Schema Part 2: Datatypes 2: It defines facilities for defining datatypes to be used in XML Schemas as well as other XML specifications.

DTDs consists of elements that text string, text string with other child elements and a set of child elements. DTDs also offer limited support for types and namespaces. Lastly, the syntax in DTDs is not XML.

XML Schema is more powerful than DTD. Advantages of XML Schema over DTDs are:

￿Defines data types for elements and attributes, and their default and fixed values. Some of the data types can be of string, decimal, integer, boolean, date, time or duration. Altogether there are 19 built-in primitive data types and 23 built-in derived data types. Primitive data types are not defined in terms of any other data types, whereas derived data types are defined in terms of other data types.

￿Apply restrictions to elements, by stating minimum and maximum values, (for example, on age from 1 to 90 years), or restrictions of certain values (eg. redbooks, residencies, Redpieces with no other values accepted, such as in a drop-down list box). Restrictions can also be applied to types of characters and their patterns (eg. only accepting values ‘a’ to ‘z’ and also specifying that only three letters can be accepted). The length of the data can also be specified. (Eg. passwords must be between 4 and 8 characters.)

￿Specify complex element type. Complex types may contain simple elements and other complex types. Restrictions can be applied to the sequence and their frequency of their occurrences. These complex types can then be used in other complex type elements.

￿Since schemas are written in XML, they are also extensible. The also implies that the learning curve for learning another language has been eliminated, the available parsers need not be enhanced, transformation can be carried out using XSLT, and also its manipulation can be carried out using XML DOM.

￿With XML Schemas being extensible, they can be re-used in other schemas, we can reference multiple schemas from the same document, and also have the ability to create our own data types from standard data types.

20 The XML Files: Development of XML/XSL Applications Using WebSphere Studio