XML Schema is an XML-based alternative to DTD.
XML Schemas are much more powerful than DTDs.
The XML Schema language is also referred to as XML Schema Definition (XSD).
One of the greatest strength of XML Schemas is the support for data types.
With support for data types:
Another great strength about XML Schemas is that they are written in XML.
Some benefits of that XML Schemas are written in XML:
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:
ensures a mutual understanding of the content, because the XML data type "date" requires the format "YYYY-MM-DD".
XML Schemas are extensible, because they are written in XML.
With an extensible Schema definition you can:
A well-formed XML document is a document that conforms to the XML syntax rules, like:
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.