XML Parsers

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XML Parsers. Overview Types of parsers Using XML parsers SAX DOM DOM versus SAX Products Conclusion. Types of Parsers. There are several different ways to categorise parsers: Validating versus non-validating parsers Parsers that support the Document Object Model
XML Parsers
  • Overview
  • Types of parsers
  • Using XML parsers
  • SAX
  • DOM
  • DOM versus SAX
  • Products
  • Conclusion
  • Types of ParsersThere are several different ways to categoriseparsers:
  • 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.)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
  • 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)
  • Parsing XMLTwo 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
  • 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
  • APIApplicationCreating 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
  • Parsing XML: DOMXML FileDOM TreeDOM 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
  • DOM Level
  • DOM Level 1
  • - 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.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
  • 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
  • Parsing XML: SAXXML FileSAX callsSAX 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
  • DOM pro and contraPRO
  • The file is parsed only once.
  • High navigation abilities : this is the aim of the DOM design.
  • More memory needed since the XML tree is in memory.
  • SAX pro and contraPRO
  • Low memory needs since the XML file is never entirely in memory
  • Can deal with XML streams
  • 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
  • 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
  • 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)
  • 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
  • The EndQuestions?Thank you!
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