An Introduction to XML Paul Donohue May 8th 2002 Hotel Senator Zürich

Overview What Is XML? Why Use XML? Defining Rules with XML Related Technologies Demonstration Summary Questions Topics we will cover

What is XML? XML = Extensible Markup Language Not a programming language An open standard for representing structured data Describes data structure and content Separates data from its presentation XML In A Nutshell

What is XML? A woman without her man is nothing A woman without her man, is nothing A woman: without her, man is nothing Markup Clarifies Data

What is XML? Some History 1969Generalized Markup Language (GML) 1980Standardized Generalized Markup Language (SGML) 1986SGML becomes ISO standard 1991Hypertext Markup Language (HTML) 1996W3C begin work on a language to combine SGML & HTML 1998XML standard is published

What is XML? A PB / XML Messaging System Mr Paul Donohue PowerBuilder Developers 13: An XML Document

What is XML? Parts of an XML document XML Declaration Prolog Elements Attributes Comments Other Parts A PB / XML Messaging System Mr Paul Donohue PowerBuilder Developers 13:

What is XML? Elements are the basic building blocks of XML XML’s nouns Elements consist of start tag, contents and end tag… cat Empty elements can be shown as Contents can be data or other elements Elements can own attributes Elements

What is XML? Attributes give further information about an element XML’s adjectives Attributes consist of name, equals and value… cat_type=“persian” Attribute values are quote delimited strings Attributes are placed inside an element’s start tag Attributes

What is XML? XML messages are text files XML is case sensitive XML uses the Unicode 2.1 character set Special codes for markup characters such as < and & Characters

What is XML? All elements and attributes are named Must begin with a letter, underscore or colon Must continue with valid name characters  Letter / Underscore / Colon  Digit  Hyphen  Full stop May not begin with “XML” Names

What is XML? XML uses tags like in HTML XML complements HTML XML is for “smart data” XML is both data and document XML vs HTML

What is XML? Sybase PowerBuilder 7.1 £ Data encoded as HTML

What is XML? Sybase PowerBuilder Data encoded as XML

Why Use XML? Royalty free Industry standard Platform & vendor independent Self describing Flexible Caters for nested & repeating data Six Good Reasons

Why Use XML? Nobody “owns” XML No software to purchase No licensing fees Royalty Free

Why Use XML? XML version 1.0 became a W3C standard in 1998 Good support from vendors Low risk technology Large community of developers Industry Standard

Why Use XML? XML documents are text based Perfect for messaging There are no vendor-specific extensions PDA to Mainframe Platform & Vendor Independent

Why Use XML? Descriptive element & attribute names The name / data combination is easy to understand GBP XML can be viewed with a text editor Self Describing

Why Use XML? XML can handle any structured data XML can be easily transformed Direct access to the required data Flexible

Why Use XML? Nested data… An employee has an address and that address has a street and a post code Repeating data… An invoice has one or more items on it Hard to do with traditional file formats Nested & Repeating Data

Defining Rules Conform to the grammar of XML  One root element  Non-empty elements have start & end tags  Elements are nested correctly  Attributes are not repeated within elements  Attribute values are quoted Can be parsed by any parser The data may be nonsense Well-Formed XML Documents

Defining Rules Must contain a valid document type declaration Must obey the constraints of that declaration  Element sequence is valid  Required attributes are provided  Attribute values are a valid value Ensures data is valid for the application domain Rules are in a DTD or schema Valid XML Documents

Defining Rules DTDs define validation rules for XML documents  Elements – contents, order & occurrence  Attributes – valid & default values DTDs are optional DTDs can be internal or external DTDs are written in XML Declaration Syntax Document Type Definitions (DTD)

Defining Rules Schemas are more powerful that DTDs  Data types  Improved occurrence constraints Schemas are written in XML Schemas can refer to other schemas Get your DTD or schema correct before you code Schemas

Defining Rules Standard terms facilitate data exchange Industry-wide standards have emerged;  MathML : Mathematical Markup Language  CML : Chemical Markup Language  FPML : Financial Products Markup Language  CDF : Channel Description Format Check if your industry or organisation has a standard Semantics

Related Technologies Parsers : SAX & DOM Searching : XPath Formatting : CSS, XSL & XSLT Linking : XLink & XPointer Resource Description Framework (RDF) Overview

Related Technologies Event driven Can handle large files No random access Read only Primarily for Java Simple API for XML (SAX)

Related Technologies Standard set of function calls XML loaded into memory Best for smaller files Data is parsed into a tree of nodes Language and platform neutral Document Object Model (DOM)

Demonstration

Summary

What XML is Why we should use XML How to define rules in XML XML’s related technologies What have we learnt?

Summary Recommended reading Title : Professional XML Author : Mark Birbeck et al Publisher : Wrox Press Inc ISBN:

Summary Recommended reading Title : Fast Track To XML Author : Eric Zenor Publisher : Sybase Article :

Summary Useful Web Sites XML Org : W3C : XML FAQ : XML Cover Pages : XML Journal :

Summary MS XML Notepad XML Spy Useful XML Tools

Questions If you have any questions about this presentation please me or visit my web site. Web :