GIST NOTES 18 - XML
[DISCLAIMER: This is solely for non-commercial use. I don't claim ownership of this content. This is a crux of all my readings studies and analysis. Some of them are excerpts from famous books/sources on the subject. Some of them are my contemplation upon experiments with direct hand coded code samples using IDE or notepad.
I've created this mainly to reduce an entire book into few pages of critical content that we should never forget. Even after years, you don't need to read the entire book again to get back its philosophy. I hope these notes will help you to replay the entire book in your mind once again.]
>The Java API for XML Processing (JAXP)
>Simple API for XML (SAX), as developed cooperatively by the members of the XML-DEV mailing list.
>SAX (Simple API for XML) is an event-based sequential access parser API developed by the XML-DEV mailing list for XML documents. SAX provides a mechanism for reading data from an XML document that is an alternative to that provided by the Document Object Model (DOM). Where the DOM operates on the document as a whole, SAX parsers operate on each piece of the XML document sequentially.
SAX parsers have certain benefits over DOM-style parsers. The quantity of memory that a SAX parser must use in order to function is typically much smaller than that of a DOM parser. DOM parsers must have the entire tree in memory before any processing can begin, so the amount of memory used by a DOM parser depends entirely on the size of the input data. The memory footprint of a SAX parser, by contrast, is based only on the maximum depth of the XML file (the maximum depth of the XML tree) and the maximum data stored in XML attributes on a single XML element. Both of these are always smaller than the size of the parsed tree itself.
Because of the event-driven nature of SAX, processing documents can often be faster than DOM-style parsers. Memory allocation takes time, so the larger memory footprint of the DOM is also a performance issue.
Due to the nature of DOM, streamed reading from disk is impossible. Processing XML documents larger than main memory is also impossible with DOM parsers, but can be done with SAX parsers. However, DOM parsers may make use of disk space as memory to sidestep this limitation. 
>SAX processor generates events on start and end of element and text nodes with attributes reported along