Lecture Outline

In this week, we shall talk about several things about XML:

• Continue the discussion about XML Web Programming using a new example.
• Show how to write an XML DTD whose content is parameterized.
• Study the content model of XML DTD in more details, especial about its deterministic content models.

The study materials are listed in the course web site. This slide set just contain some pointers.

How to Parameterize a DTD?

• Use parameter entity: Instead of hard-coding the content model of an element type, one can use parameter entity declarations to associate a "name" to a "part" (which is just a string) in the content model. Later, a parameter entity reference can be used to substitute this part in the actual definition of the content model for the element type.
• Use conditional inclusion: The IGNORE and INCLUDE directives can be used to ignore and include portions of DTD, respectively.
• One can combine the use of parameter entity and conditional inclusion!
• Better yet, parameter entities can be redefined!
• A question of precedence: In the event of conflicting entity declarations, the first one encountered takes precedence. Especially,
  • If two parameter entity declarations appear in the same file, the first takes precedence.
  • Whatever appear in the internal DTD subset take precedence over what are in the original DTD.

Parameterized DTD, Examples

• Here is an example in combining parameter entity and conditional inclusion:
  

  <!ENTITY % notes_allowed "INCLUDE">
  
  <![%notes_allow;[
   <!ELEMENT production_note (#PCDATA)>
  ]]>
  

• Read pp. 54-56 and pp. 122-139 of XML in a Nutshell, third edition, by Elliotte Rusty Harold and W. Scott Means, for descriptions and examples.