Architecture

Although the DOM Architecture can be used for the creation of new documents not residing in some external resource, a DOM Implementation is usually not a piece of stand-alone software: in most cases, it is added as a separation layer between a XML parser and user applications. The distinction between the parser and the DOM implementation is not always so definite. For example, a DOM implementation can provide its own parsing module, so that the DOM layer appears as the lowest one from the application point of view. Alternatively, the XML parser could only be responsible to generate a proper sequence of SAX events, and then it is up to the DOM implementation to create the internal document representation. As we will see, the approach used in Gdome2 is somehow an hybrid of the two scenarios previously depicted. In fact, Gdome2 is based on the XML C library for Gnome (libxml2⁴ for short) which is much more than an mere XML parser. With respect to parsing, libxml2 exports three kinds of interfaces:

• a SAX event-based interface;
• a Pull method, which parses a whole document and then returns a corresponding document structure;
• a Push method, where the document is parsed on demand, as the application requires for more chunks to be parsed. This method is conceived to be used, for example, in interactive applications where it is not feasible to block the whole process while parsing a large document.

In particular, the last two methods build a libxml2-dependent tree representation of the document which largely borrows from the DOM core specification, and this is a crucial aspect of the whole Gdome2 implementation, as we will see.

Footnotes

... (libxml2⁴

http://xmlsoft.org