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Narrative

Steve divides the application into four parts:

1. Core XML Processing

Five Java packages provide functions for representing and manipulating XML documents (including controlling, but not actually performing, parsing):

• XML Atoms (package xa) to encapsulate low-level knowledge of the XML language itself. While normally embedded in parsers themselves, the idea is to allow other software (eg. an editor) to use this information.
• Grove (xg). Nothing revolutionary here!
• XML Manipulator (xm) provides a range of document manipulation capabilities, including factory classes, a base parsing 'engine' class, and document model and document listener classes (to co-ordinate changes made in multiple document views). This package also contains the 'node type registry' for specialised element and other classes.
• Customizer (xc), fulfilling the same role as JavaBean customizers via a collection of classes to display and edit the standard types of XML entities.
• View (xv), containing swing.text.View classes to be used for display elements in a Swing styled editor.

Any supported parser can drive the application, in a similar manner to SAX, but at a higher level. (SAX is, however, a supported 'parser'). The engine generates the xg grove as the parse proceeds, and also supports a progress bar (if the parser provides the necessary position information - which SAX does not).

Steve's own parser (package xe) is not covered in this presentation, but follows the lead of the other packages of dividing its processing among many classes; it has a parser class for each type of XML entity (and allows new parser classes to be added via the node type registry). This parser is incomplete, is not fast, and is non-validating, but functions reasonably well in practice.

3. Specialised XML Usages

The vanilla application manipulates vanilla XML documents, but semantic knowledge can be embedded in specialised classes. Three such usages are implemented: an XSL engine (incomplete), UI configuration, and rendering a database schema in XML via JDBC. The basis for expandability is to 'register' information about specific XML element types:

• Element class name. Specialised element classes can contain whatever specialised processing they wish. Such processing can be invoked as part of the parse by calling the 'verify()' method on each element when its parsing is complete.
• Customizer class name, for specialised display and editing.
• Parser class name, primarily to allow special PI parsers to be slotted in.
• View class name, meaning a swing.text.View class to be used for styled display and editing of an XML document. (See the xv package.)

These ideas are brought together in the XML Testbed application (package xt), which implements them all and is also a basic XML authoring environment.

There is also an Online Help package (oh) containing a frame class for the display of HTML help. This also uses the xu package to configure its user interface, especially the menu of what help options are available. (A toolbar can be added simply by editing its XML configuration file, after obtaining the images to display on its buttons.)