Example: Restrict the content model for the <topic> element using DTD

This section is non-normative.

In this scenario, the DITA architect for Acme Incorporated wants to redefine the content model for the topic document type. They want to omit certain elements, make the <shortdesc> element required, and disallow topic nesting.

Specifically, the DITA architect wants to redefine the content model in the following ways:

• Remove <abstract>
• Require <shortdesc>
• Remove <related-links>
• Remove the %task-info-types; entity in order to disallow topic nesting

1. The DITA architect creates a constraint module: acme-TopicConstraint.mod.
2. They add the following content to acme-TopicConstraint.mod:

   
   <!-- ============================================================= -->
   <!--                    CONSTRAINED TOPIC ENTITIES                 -->
   <!-- ============================================================= -->
   
   <!-- Declares the entities referenced in the constrained content  -->
   <!-- model.                                                       -->
   
   <!ENTITY % title            "title">
   <!ENTITY % shortdesc        "shortdesc">
   <!ENTITY % prolog           "prolog">
   <!ENTITY % body             "body">
   
   <!-- Defines the constrained content model for <topic>.            -->
   
   <!ENTITY % topic.content
                          "((%title;),
                            (%shortdesc;), 
                            (%prolog;)?, 
                            (%body;)?)"
   >

3. They add the constraint module to the catalog.xml file.
4. They then integrate the constraint module into the document-type shell for topic by adding the following content to the "Element-Type Configuration Integration section:

   <!-- ============================================================= -->
   <!--           ELEMENT-TYPE CONFIGURATION INTEGRATION              -->
   <!-- ============================================================= -->
   
   <!ENTITY % topic-constraints-c-def  
     PUBLIC "-//ACME//ELEMENTS DITA Topic Constraint//EN" 
     "acme-TopicConstraint.mod">
   %topic-constraints-c-def;

5. They check their test topic to ensure that the content model is modified as expected.