Document Type Definitions

A document type definition is used to describe the format of valid XML documents
It can be used to verify XML documents
It can be used to parse XML documents decomposing them into a tree
Defines allowed elements
For each element defines content and supported attributes
Specified element content can be

Parsed character data

Indicated by #PCDATA

Child element

Indicated (name)

Sequence of elements

Indicated by (child1, child2, ...)

Zero or one child elements

Indicated by name?

Zero or more child elements

Indicated by name*

One or more child elements

Indicated by name+

A choice among different child elements

Indicated by (name1 | name2 | ...)

Example:

  <!ELEMENT booklist (book)*>
    <!ELEMENT book (isbn,title,author+,price,edition?)*>
      <!ELEMENT isbn (#PCDATA)>
      <!ELEMENT title (#PCDATA)>
      <!ATTLIST title lang (german|english) "german">
      <!ELEMENT author (givenname,familyname)>
        <!ELEMENT givenname (#PCDATA)*>
        <!ELEMENT familyname (#PCDATA)>
      <!ELEMENT price (#PCDATA)>
      <!ELEMENT edition (#PCDATA)>