XSLT

Chapter 5. Creating Links and Cross-References

If you’re creating a web site, publishing a book, or creating an XML transaction, chances are many pieces of information will refer to other things. This chapter discusses a several ways to link XML elements. It reviews three techniques:

• Using the id() function

• Doing more advanced linking with the key() function

• Generating links in unstructured documents

Generating Links with the id() Function

Our first attempt at linking will be with the XPath id() function.

The ID, IDREF, and IDREFs Datatypes

Three of the basic datatypes supported by XML Document Type Definitions (DTDs) are ID, IDREF, and IDREFS. Here’s a simple DTD that illustrates these datatypes:

<!--glossary.dtd-->
<!--The containing tag for the entire glossary-->
<!ELEMENT glossary  (glentry+) >

<!--A glossary entry-->
<!ELEMENT glentry  (term,defn+) >

<!--The word being defined-->
<!ELEMENT term  (#PCDATA) >
<!--The id is used for cross-referencing, and the 
    xreftext is the text used by cross-references.-->
<!ATTLIST term
               id  ID    #REQUIRED 
               xreftext  CDATA    #IMPLIED  >

<!--The definition of the term-->
<!ELEMENT defn  (#PCDATA | xref | seealso)* >

<!--A cross-reference to another term-->
<!ELEMENT xref   EMPTY  >

<!--refid is the ID of the referenced term-->
<!ATTLIST xref
               refid  IDREF    #REQUIRED >

<!--seealso refers to one or more other definitions-->
<!ELEMENT seealso EMPTY>
<!ATTLIST seealso
                  refids   IDREFS  #REQUIRED >

In this DTD, each <term> element is required to have an id attribute, ...