Example: Redefine the content model for the <topic> element

In this scenario, an information architect for Acme, Incorporated wants to redefine the content model for the topic document type. She wants to omit the <abstract> element and make the <shortdesc> element required; she also wants to omit the <related-links> element and disallow topic nesting.

  1. She creates a .mod file using the following naming conventions: qualiferTagnameConstraint.mod, where qualifer is a string the describes the constraint, and Tagname is the element type name with an initial capital. Her contraint module is named acme-TopicConstraint.mod.
  2. She adds the following content to acme-TopicConstraint.mod:
    <!-- ============================================================= -->
<!--                    CONSTRAINED TOPIC ENTITIES                 -->
<!-- ============================================================= -->

<!-- Declares the entity for the constraint module and defines     -->
<!-- its contribution to the @domains attribute.                   -->

<!ENTITY topic-constraints     
  "(topic basic-Topic-c)"
>

<!-- Declares the entities referenced in the constrained content  -->
<!-- model.                                                       -->

<!ENTITY % title            "title">
<!ENTITY % titlealts        "titlealts">
<!ENTITY % shortdesc        "shortdesc">
<!ENTITY % prolog           "prolog">
<!ENTITY % body             "body">

<!-- Defines the constrained content model for <topic>.            -->

<!ENTITY % topic.content
                       "((%title;), 
                         (%titlealts;)?,
                         (%shortdesc;), 
                         (%prolog;)?, 
                         (%body;)?)"
>
  3. She then integrates the constraint module into her document-type shell for topic by adding the following section above the "TOPIC ELEMENT INTEGRATION" comment:
    <!-- ============================================================= -->
<!--                    CONTENT CONSTRAINT INTEGRATION             -->
<!-- ============================================================= -->

<!ENTITY % topic-constraints-c-def  
  PUBLIC "-//ACME//ELEMENTS DITA Topic Constraint//EN" 
  "acme-TopicConstraint.mod">
%topic-constraints-c-def;
  4. She then adds the constraint to the list of domains and constraints that need to be included in the value of the @domains attribute for <topic>:
    <!-- ============================================================= -->
<!--                    DOMAINS ATTRIBUTE OVERRIDE                 -->
<!-- ============================================================= -->

<!ENTITY included-domains 
                          "&hi-d-att; 
                           &ut-d-att; 
                           &indexing-d-att;
                           &topic-constraints;
  "
>
  5. After updating the catalog.xml file to include the new constraints file, her work is done.