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XML - PowerPoint PPT Presentation


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XML. eXtensible Markup Language. XML. A method of defining a format for exchanging documents and data. Allows one to define a dialect of XML A library of tags, with associated structure. <config> <descriptor type="FILE" name="source"> <attribute name="media\_type" type="svalue"/>

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PowerPoint Slideshow about 'XML' - marlin


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XML

eXtensible Markup Language

slide2
XML
  • A method of defining a format for exchanging documents and data.
    • Allows one to define a dialect of XML
    • A library of tags, with associated structure

the social benefits
The Social Benefits
  • Can specify an interchange format concisely and accurately enough to set up a validation service easily
  • There is plenty of available software for dealing with XML files and translating from one format into another
downsides
Downsides
  • Sometimes defining a representation can be a pain
    • Deciding what to leave as content and what to move to attributes.
    • XML Schemas are confusing, while DTDs do not offer enough control
  • Verbose
    • ViPER increased about 2x uncompressed, 4/3x gzip compressed
  • Difficult to read
    • Lots of and end tags get in the way of the data
the real benefits to the programmer
The Real Benefits to The Programmer
  • XML Schema (or DTDs) allow you to validate a document without having to examine it
  • Xpath allows you to specify a node, or set of nodes, in a document quickly and easily
  • SAX makes it easy to write a quick parser
  • DOM makes it so you don’t even have to do that
  • XSL:T allows you to transform from an XML document into another document, possibly not even standard XML
  • Etc.
xml as a file format
XML As A File Format
  • Makes parsing simpler, but currently no methods for making saving easier
  • Saves you from dealing with things like character encoding and date formatting
  • No more difficult than making up your own
  • An unfamiliar or forgotten file grants more affordances than an XML or binary file
defining a dialect
Defining A Dialect
  • XML Schema – Structure and Data
    • Define elements and attributes
    • Associate them with data types

targetNamespace="http://lamp.cfar.umd.edu/viper"

xmlns:viper="http://lamp.cfar.umd.edu/viper"

elementFormDefault="qualified">

schema datatypes
Schema Datatypes
  • Can create and assign datatypes to attributes and elements. For example:

schema structures
Schema Structures
  • Can specify order and contents of elements
    • Sequence, choice, mixed, etc. allow specifying how and where elements appear
    • Substitution groups allow one tag to take the place of another
  • Can group elements without placing the into types
extensiblity
Extensiblity
  • Inheritance
    • Can extend complex elements by adding more attributes and elements to the bottom
    • Can restrict the data using the elements
  • The and elements
    • The ultimate in extensibility, allow any valid XML in from a given namespace or range of namespaces
parsing
Parsing
  • Using the DOM:
    • The DOM provides a tree structure that represents the document
    • Memory heavy
  • Using SAX:
    • Event driven
    • Lightweight
    • Better for large documents
xpath
Xpath
  • The common language for selecting individual pieces of an XML document shared between X-Link and XSL:T
    • Also used for defining uniqueness constraints in Schemas
    • DOM Level 3 will support selecting by Xpath
  • Looks sort of like a JavaScript DOM call:
    • /viper/config/descriptor[@type=“FILE”]
      • Selects all of the file descriptor nodes that are of type “FILE”
resources
Resources
  • www.xml.com
    • O'Reilly's XML resource
  • www.w3.org
    • The standards themselves, and lots of good links to implementations.
  • xml.apache.org
    • DOM, SAX, and XSLT for C and Java
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