Editing XML schema (section)

==== Disadvantages ====

W3C XML Schema is complex and hard to learn, although that is partially because it tries to do more than mere validation (see [[PSVI]]).

Although being written in XML is an advantage, it is also a disadvantage in some ways. The W3C XML Schema language, in particular, can be quite verbose, while a DTD can be terse and relatively easily editable.

Likewise, WXS's formal mechanism for associating a document with a schema can pose a potential security problem. For WXS validators that will follow a [[URI]] to an arbitrary online location, there is the potential for reading something malicious from the other side of the stream.<ref name="clark">James Clark (co-creator of RELAX NG). [http://www.imc.org/ietf-xml-use/mail-archive/msg00217.html RELAX NG and W3C XML Schema] {{webarchive |url=https://web.archive.org/web/20070927235958/http://www.imc.org/ietf-xml-use/mail-archive/msg00217.html |date=September 27, 2007 }}</ref>

W3C XML Schema does not implement most of the DTD ability to provide data elements to a document.

Although W3C XML Schema's ability to add default attributes to elements is an advantage, it is a disadvantage in some ways as well. It means that an XML file may not be usable in the absence of its schema, even if the document would validate against that schema. In effect, all users of such an XML document must also implement the W3C XML Schema specification, thus ruling out minimalist or older XML parsers. It can also slow down the processing of the document, as the processor must potentially download and process a second XML file (the schema); however, a schema would normally then be cached, so the cost comes only on the first use.