OpenEdge Development: Working with XML - Product ...

Reading and Writing XML with the Document Object Model (DOM)
The ABL DOM interface
2–6
The Document Object Model (DOM) is the original application programming interface (API)
for XML documents, as defined by the W3C. It continues to be the W3C recommendation.
Note: Chapter 1, “Developing with XML in OpenEdge,” provides a comparative
introduction to the ABL DOM interface. See this chapter if you are currently
evaluating which ABL features best meet your needs for handling XML documents in
ABL applications.
A software module called an XML parser is used to read XML documents and provide access
to their content and structure. The XML parser does its work on behalf of another software
module—your application. ABL simplifies your interaction with DOM and its parser by
providing the familiar ABL programming constructs of built-in objects, handles, attributes, and
methods. This section describes the ABL objects that make up the DOM interface.
Note: The DOM API is designed to be compatible with a wide range of programming
languages. In implementing DOM within the ABL, Progress Software Corporation
adapted the specification to fit smoothly into the ABL environment. In some cases, the
World Wide Web Consortium (W3C) naming conventions conflicted with familiar
ABL naming conventions. In other cases, functionality in the DOM specification was
already available in ABL. In all these cases, the established ABL naming and
functionality was preserved.
Prerequisites
The ABL DOM interface is most quickly employed if:
• You understand XML
• You understand DOM programming
• You understand ABL programming including the use of built-in objects and their handles,
methods, and attributes
If you have not yet learned XML, then DOM programming is not a productive starting point for
you. Take the time to learn basic XML with any one of the many online or printed tutorials.
If you understand DOM, then you will find the ABL implementation to be a useful one that
implements all the features of DOM that are needed by an ABL programmer. It is not a complete
implementation of the entire DOM specification.
If you are not a DOM programmer, you can use this chapter to understand the ABL
implementation and to develop pragmatic skills for reading and writing XML documents, as
well as building XML documents or fragments in memory. The ABL implementation takes a
somewhat difficult technology and makes it much easier to exploit within the ABL
environment.