XML Document Type Definition

The DTD can define the allowed syntax for all documents. For example, the following is the Open Software Description (OSD) DTD -- this is a proposed standard for "... describing software packages and their dependencies for heterogeneous clients."

<!ELEMENT ABSTRACT (#PCDATA)>

<!ELEMENT CODEBASE EMPTY>
  <!ATTLIST CODEBASE FILENAME CDATA #IMPLIED>
  <!ATTLIST CODEBASE HREF CDATA #REQUIRED>
  <!ATTLIST CODEBASE SIZE CDATA #IMPLIED>

<!ELEMENT DEPENDENCY (CODEBASE|SOFTPKG)* > 
  <!ATTLIST DEPENDENCY ACTION (Assert|Install) "Assert">

<!ELEMENT DISKSIZE EMPTY>
  <!ATTLIST DISKSIZE VALUE CDATA #REQUIRED>

<!ELEMENT IMPLEMENTATION (CODEBASE | DEPENDENCY | DISKSIZE | 
  IMPLTYPE | LANGUAGE | OS | PROCESSOR | VM)*>

<!ELEMENT IMPLTYPE EMPTY>
  <!ATTLIST IMPLTYPE VALUE CDATA #REQUIRED>

<!ELEMENT LANGUAGE EMPTY>
  <!ATTLIST LANGUAGE VALUE CDATA #REQUIRED>

<!ELEMENT LICENSE EMPTY>
  <!ATTLIST LICENSE HREF CDATA #REQUIRED>

<!ELEMENT MEMSIZE EMPTY>
  <!ATTLIST MEMSIZE VALUE CDATA #REQUIRED>

<!ELEMENT OS (OSVERSION)*> 
  <!ATTLIST OS VALUE CDATA #REQUIRED>

<!ELEMENT OSVERSION EMPTY> 
  <!ATTLIST OSVERSION VALUE CDATA #REQUIRED>

<!ELEMENT PROCESSOR EMPTY> 
  <!ATTLIST PROCESSOR VALUE CDATA #REQUIRED>

<!ELEMENT SOFTPKG (ABSTRACT | IMPLEMENTATION | DEPENDENCY | LICENSE | 
  TITLE)*>
  <!ATTLIST SOFTPKG NAME CDATA #REQUIRED>
  <!ATTLIST SOFTPKG VERSION CDATA #IMPLIED>

<!ELEMENT TITLE (#PCDATA) >

<!ELEMENT VM EMPTY>
  <!ATTLIST VM VALUE CDATA #REQUIRED>