1. XML Parsers Overview Types of parsers Using XML parsers SAX DOM
DOM versus SAX
Products
Conclusion

2. Types of Parsers There are several different ways to categorise
Validating versus non-validating parsers
Parsers that support the Document Object Model
(DOM)
Parsers that support the Simple API for XML (SAX)
Parsers written in a particular language (Java, C++,
Perl, etc.)

3. Non-validating Parsers
Speed and efficiency
It takes a significant amount of effort for an XML parser to process a DTD and make sure that every element in an XML document follows the rules of the DTD.
If only want to find tags and extract information - use non-validating

4. Using XML Parsers Three basic steps to use an XML parser
Create a parser object
Pass your XML document to the parser
Process the results
Generally, writing out XML is outside scope of parsers (though some may implement proprietary mechanisms)

5. Parsing XML Two established API's: SAX (Simple API for XML)
Define handlers containing methods as XML parsed
DOM (Document Object Model)
Defines a logical tree representing the parsed XML

6. Parsing XML: DOM Document Object Model
standard API for accessing and creating XML data
tree-based
programming language indepedent
developed by W3C
whole document is read into memory
read and write

7. Creating a DOM Tree
A DOM implementation will have a method to pass a XML file to a factory object that will return a Document object that represents root element of whole document
After this, may use DOM standard interface to interact with XML structure
A P I
Application

8. Parsing XML: DOM
XML File
DOM Tree

9. DOM Interfaces The DOM defines several interfaces
Node The base data type of the DOM
Element Represents element
Attr Represents an attribute of an element
Text The content of an element or attribute
Document Represents the entire XML document. A Document object is often referred to as a DOM tree

10. DOM Level - basic functionality for document navigation and
manipulation.
DOM Level 2
- includes a style sheet object model
- defines an event model and provides support for
XML namespaces.
DOM Level 3
- still under development
- addresses document loading and saving
- content model (DTDs and schemas) with document validation
support.

11. Parsing XML: SAX Simple API for XML API for accessing xml data
event based
programming language indepedent
application has to store fragments into memory
read only

12. Parsing XML: SAX
SAX is an interface to the XML parser based on streaming and call-backs
You need to implement the HandlerBase interface :
startDocument, endDocument
startElement, endElement
characters
warning, error, fatalError

13. Parsing XML: SAX
XML File
SAX calls

14. SAX versus DOM DOM: read and write need to move back and forth in data
document is human created
SAX:
read only
huge data or streams
data is machine generated

15. DOM pro and contra PRO The file is parsed only once.
High navigation abilities : this is the aim of the DOM design.
CONTRA
More memory needed since the XML tree is in memory.

16. SAX pro and contra
PRO
Low memory needs since the XML file is never entirely in memory
Can deal with XML streams
CONTRA
The file has to be parsed entirely to access any node. Thus, getting the 10 nodes included in a catalog ended up in parsing 10 times the same file.
Poor navigation abilities : no way to get easily the children of a given node or the list of "B" nodes

17. SAX versus DOM
If your document is very large and you only need a few elements - use SAX
If you need to process many elements and perform operations on XML - use DOM
If you need to access the XML many times use DOM

18. Parser Products Xerces4J / Xerces4C++ (Apache) James Clark’s XP (Java)
IBM XML4J / XML4C++
Java Project X (Sun)
Oracle’s XML Parser for Java
MSXML (Microsoft)
Dan Connolly’s XML Parser (Phyton) …

19. Conclusion The parser is key building block for every XML application.
When building XML applications, you have to think how will you handle large chunks of data
Choosing between SAX and DOM is not always trivial

20. The End
Questions?
Thank you!