XML

title

Web Services Basics For Non-programmers

author

Pete George (NobleProg Ltd)

Day One Schedule ⌘

1. Introductions
2. Service-Oriented Architecture
3. Web Services Overview
4. XML
5. SOAP

XML ⌘

Learning Objectives

• To appreciate the advantages and disadvantages of using XML for Web services
• To understand the basic structure of an XML message
• To be aware of Xpath, XSD and XSLT

XML Messaging ⌘

XML eXtensible Markup Language ⌘

• W3C Recommendation 1998
• Most common method for data exchange

eXtensible Markup Language ⌘

eXtensible Markup Language ⌘

• Markup language, like HTML

Why XML and Web Services? ⌘

• Data not presentation
• Interoperability
• Resilience
• Easily readable

Why XML and Web Services? ⌘

• Data not presentation

Why XML and Web Services? ⌘

• Interoperability

-Easy to agree XML format for data exchange

-High availability of XML parsers

-No need for low-level code to read/write data

Why XML and Web Services? ⌘

XML is more resilient

Why XML and Web Services? ⌘

• Easily readable

Easily Readable? ⌘

Elements and Attributes ⌘

• Elements, e.g.

<Users> some users </User>

• Attributes, e.g.

<user name=“Pete”> User1 </user> or <user name=“Pete”/>

Elements and Attributes ⌘

Root Element ⌘

• Well-formed XML has one element at root

<rootElement>
 <anotherElement anAttribute=“some data”>
 </anotherElement>
</rootElement>

Root Element ⌘

XML Prolog ⌘

• XML Prolog

<?xml version=“1.0”?>

-Optional, but usually declared

-May contain other information, e.g.

<?xml version=“1.0” encoding=“UTF-8”?>

XML Prolog ⌘

Namespaces ⌘

• Group XML elements together

• Declare namespace

xmlns=<URI>

-E.g. xmlns:PETE=http://pa-uk.net/etc <PETE:users >

Namespaces ⌘

• URI = Uniform Resource Identifier

-String that points to something

• Can be:

-URL = Uniform Resource Locator

-Specifies location of a resource

-[scheme]://[Domain]:[Port]/[Path]?[Querystring]#[FragmentId]

-URN = Uniform Resource Name

-Uniquely identifies something

-urn:[namespace identifier]:[namespace specific string]

Namespaces ⌘

Comments ⌘

• Comments can also be included

< !--This is a comment-- >

Entity References ⌘

• Illegal characters can be used by inserting entity references

& = &

< = &lt;

> = &gt;

“ = &quot;

‘ = &apos;

XPath ⌘

• XML Path Language
• Query language used to target specific elements or attributes
• Works like file system paths:

<users>
  <user name=“Pete” />
</users>

XPath = /Users/user

XPath ⌘

XML Document Definition ⌘

• Describe structure of XML document
• Used to test XML document is valid
• Used to author XML document in editor

• Document Type Definition (DTD)

-Widespread but on decline

-Not in XML format

XML Schema (XSD) ⌘

• Defines rules XML document must conform to be considered 'valid’

• Advantages over DTD:

-In XML format

-Namespace aware

-Data type aware

• defines elements/attributes containing values such as integers

XSLT ⌘

• Extensible Stylesheet Language Transformations
• Transforms XML file into new XML file in new style
• Can transform XML into other forms, e.g. XHTML

XML Disadvantages ⌘

Quiz – No Prizes! No Pressure! ⌘