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Intro to XML

Intro to XML. Originally Presented by Clifford Lemoine Modified by Box. Introduction to XML. Review of XML What is different XML parsing? Simple Example program Wrap-up References. Quick XML Review. XML – Wave of the future Method of representing data

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Intro to XML

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  1. Intro to XML Originally Presented by Clifford Lemoine Modified by Box

  2. Introduction to XML • Review of XML • What is different XML parsing? • Simple Example program • Wrap-up • References

  3. Quick XML Review • XML – Wave of the future • Method of representing data • Differs from HTML by storing and representing data instead of displaying or formatting data • Tags similar to HTML tags, only they are user-defined • Follows a small set of basic rules • Stored as a simple ASCII text file, so portability is insanely easy

  4. Quick XML Review • Syntax • Every XML document has a preamble • <?xml version=“1.0” ?> • An XML document may or may not have a DTD (Document Type Definition) or Schema • <!DOCTYPE catalog>

  5. Quick XML Review • Syntax cont. • Every element has a start and end tag, with optional attributes • <catalog version=“1.0”> … </catalog> • If an element does not contain any data (or elements) nested within, the closing tag can be merged with the start tag like so: • <catalog version=“1.0”/>

  6. Quick XML Review • Syntax cont. • Elements must be properly nested • The outermost element is called the root element • An XML document that follows the basic syntax rules is called well-formed • An XML document that is well-formed and conforms to a DTD or Schema is called valid • Once again, XML documents do not always require a DTD or Schema, but they must be well-formed

  7. Quick XML Review • Sample XML files • Catalog.xml

  8. <?xml version="1.0"?> <catalog library="somewhere"> <book> <author>John Doe</author> <title>Title 1</title> </book> <book> <author>Phill Smith</author> <title>His One Book</title> </book> <magazine> <name>PC Mag</name> <article page="17"> <headline>Second Headline</headline> </article> </magazine> </catalog>

  9. Let’s work in our project input • Back to our original class diagram (network configuration) • Define your input • xml\net.xml

  10. What is XML Parser? • A program or module that checks a well-formed syntax and provides a capability to manipulate XML data elements. • Navigate thru the XML document (DOM or SAX) • extract or query data elements • Add/delete/modify data elements

  11. XML Parsing • DOM (Document Object Model). • Reads the whole document and builds DOM tree. • Simple API for XML = SAX • SAX is an event-based parsing method • reads an XML document, firing (or calling) callback methods when certain events are found (e.g. elements, attributes, start/end tags, etc.) • Pull parser (won’t talk more here)

  12. DOM vs. SAX Parsing? • Unlike DOM (Document Object Model), SAX does not store information in an internal tree structure • Because of this, SAX is able to parse huge documents (think gigabytes) without having to allocate large amounts of system resources • Really great if the amount of data you’re looking to process is relatively large (no waste of memory on tree) • If processing is built as a pipeline, you don’t have to wait for the data to be converted to an object; you can go to the next process once it clears the preceding callback method

  13. DOM vs. SAX Parsing? • Most limitations are the programmer’s problem, not the API’s • SAX does not allow random access to the file; it proceeds in a single pass, firing events as it goes • Makes it hard to implement cross-referencing in XML (ID and IDREF) as well as complex searching routines

  14. XML Parser implementations • Apache.org Xerces package at http://xml.apache.org/ • JDOM.org jdom package www.jdom.org

  15. Simple Example Program • WarReader.java • Build document from xml file. • SAXBuilder builder = new SAXBuilder(); • Document doc = builder.build(new File(filename)); • Get the root element (node) • Element root = doc.getRootElement(); • Get children of the root • List servlets = root.getChildren("servlet"); • Iterate thru each child and extract more detailed info • xml\WarReader.java

  16. Using XML for your Final Term Project • Each team spends 10 mins to come up with data structure and XML representation • xml\NetReader.java • Demonstration here

  17. References Gittleman, Art. Advanced Java: Internet Applications (Second Edition). Scott Jones Publishers. El Granada, California. 2002. pp. 504-511. "JDOM Makes XML Easy" slides from JavaOne 2002, http://www.servlets.com/speaking/descriptions.html#jdom Janert, Phillip K. “Simple XML Parsing with SAX and DOM.” http://www.onjava.com/pub/a/onjava/2002/06/26/xml.html Published June 26, 2002. Accessed February 10, 2003. Wati, Anjini. “E-Catalog for a Small to Medium Enterprise.” http://ispg.csu.edu.au/subjects/itc594/reports/Tr-005.doc Accessed February 10, 2003.

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