Document Type Definition

A schema definition language for XML

Declaration

1. Element <>

Element Declaration §

<!ELEMENT book (title, author*, publisher?, year?, section*)>

• the element book must contain the following child elements, in order:
  1. one title
  2. zero or more authors
  3. zero or one publisher
  4. zero or one year
  5. zero or more sections

<!ELEMENT p (#PCDATA | p | ul | dl | table | h1 | h2 | h3)* >

• element p may contain:
  • {dtd}#PCDATA pure text only (no child elements)
  • p elements
  • ul elements
  • etc.
  • * → and zero or more repetitions of them.

Attribute Declaration §

<!ATTLIST img
   src    CDATA          #REQUIRED
   id     ID             #IMPLIED
   sort   CDATA          #FIXED "true"
   print  (yes | no)     "yes"
>

• Type is…
  • ID: is the unique id of that element.
    • ! ID is globally unique, regardless of attribute name, element name, etc.
    • See xml - DTD - uniqueness of ID attributes - Stack Overflow
  • IDREF: reference of some id
  • CDATA: any string
  • (val1|…): can only be either of these values.
• Value is…
  • #REQUIRED: necessary
  • #IMPLIED: optional
  • #FIXED: constant
  • ⇒ “Final column "default": default value of that attribute