====== Why Use XML Schemas? ======

XML Schemas are much more powerful than DTDs.

===== XML Schemas Support Data Types =====

One of the greatest strength of XML Schemas is the support for data types.

With support for data types:

  * It is easier to describe allowable document content
  * It is easier to validate the correctness of data
  * It is easier to work with data from a database
  * It is easier to define data facets (restrictions on data)
  * It is easier to define data patterns (data formats)
  * It is easier to convert data between different data types

===== XML Schemas use XML Syntax =====

Another great strength about XML Schemas is that they are written in XML.

Some benefits of that XML Schemas are written in XML:

  * You don't have to learn a new language
  * You can use your XML editor to edit your Schema files
  * You can use your XML parser to parse your Schema files
  * You can manipulate your Schema with the XML DOM
  * You can transform your Schema with XSLT

===== XML Schemas Secure Data Communication =====

When sending data from a sender to a receiver, it is essential that both parts have the same "expectations" about the content.

With XML Schemas, the sender can describe the data in a way that the receiver will understand.

A date like: "03-11-2004" will, in some countries, be interpreted as 3.November and in other countries as 11.March.

However, an XML element with a data type like this:

<date type="date">2004-03-11</date>

ensures a mutual understanding of the content, because the XML data type "date" requires the format "YYYY-MM-DD".

===== XML Schemas are Extensible =====

XML Schemas are extensible, because they are written in XML.

With an extensible Schema definition you can:

  * Reuse your Schema in other Schemas
  * Create your own data types derived from the standard types
  * Reference multiple schemas in the same document

===== Well-Formed is not Enough =====

A well-formed XML document is a document that conforms to the XML syntax rules, like:

  * it must begin with the XML declaration
  * it must have one unique root element
  * start-tags must have matching end-tags
  * elements are case sensitive
  * all elements must be closed
  * all elements must be properly nested
  * all attribute values must be quoted
  * entities must be used for special characters

Even if documents are well-formed they can still contain errors, and those errors can have serious consequences.

Think of the following situation: you order 5 gross of laser printers, instead of 5 laser printers. With XML Schemas, most of these errors can be caught by your validating software.