Introduce to XML

Introduction

Nguyễn Đăng Khoa

Content

• What is XML?• Well-Formed XML• XML Namespaces

What is XML?

• Stands for Extensible Markup Language• First draft was published in 1996• A revised version as recommendation on Feb

10, 1998 (by W3C)• XML derived as a subset of SGML (Standard

Generalized Markup Language)

XML’s goals

• Before XML– Data formats were proprietary

• Goals:– To make data more interchangeable– Is readable by both humans and machines

Data-centric vs. Document-centric

• 2 main types of XML formats– Store pure data: configuration– Add metadata to documents: XHTML

Advantages

• A clear separation between data and presentation

• Easy extensibility of XML files• Hierarchical Data Representation• Interoperability

Disadvantages

• Increase in the size of the file

XML In Practice

• Configuration Files• Web Services• Web Content (XHTML)• Document Management• Database Systems• Image Representation• Business Interoperability

Well-Formed XML

Well-Formed XML - XML Prolog

Well-Formed XML - XML Prolog• Optional• Must come first

• version• 1.0 (default) or 1.1

• encoding• UTF-8 (default) or

variety of Unicode• standalone• yes (default) or no

Well-Formed XML - Comment

Well-Formed XML - Comment• Human read <!-- comment -->

Well-Formed XML – Root element

Well-Formed XML – Root element• Must have one and only

one in document• Everything else lies

under this element to form a hierarchical tree

Well-Formed XML – Elements

Well-Formed XML – Elements• Basic building blocks• Can be used to show

individual or repetitive items of data

• 2 ways to define <element>

content </element> <element />

Well-Formed XML – Elements• All elements must be nested

underneath the root element• You can’t have the end tag of

an element before the end tag of one nested below it<myElement><elementA>

<elementB></elementA></elementB>

</myElement>

Well-Formed XML – Naming Styles• Pascal-casing

<MyElement />• Camel-casing

<myElement />• Underscored names

<my_element />• Hyphenated names

<my-element />

Well-Formed XML – Naming Specifications

• can begin with either an underscore or an uppercase or lowercase letter from the Unicode character set

• Subsequent characters can also be a dash (-) or a digit

• Case-sensitive• the start and end tags

must match exactly• cannot contain spaces

Well-Formed XML – Naming Specifications - Examples

Well-Formed XML – Naming Specifications - Examples

Well-Formed XML – Exercise

• <list><title>The first list</title><item>An item</list>

• <item>An item</item><item>Another item</item>

• <para>Bathing a cat is a <emph>relatively</emph> easy task as long as the cat is willing.</para>

• <bibl><title>How to Bathe a Cat<author></title>Merlin Bauer<author></bibl>

Well-Formed XML - Attributes

Well-Formed XML - Attributes• name-value pairs

associated with an element

Well-Formed XML – Attributes - Rules• consist of a name and a

value separated by an equals sign

• The name follows the same rules as element names

• The value must be in quotes

• There must be a value part• Attribute names must be

unique per element

Well-Formed XML – Attributes - Examples

Well-Formed XML – Attributes - Examples

Well-Formed XML – Character content - Restrictions

Well-Formed XML – Character content - Restrictions

• Ampersand (&)• Left angle bracket (<)

Well-Formed XML – Entity and Character References

• There are two ways of inserting characters into a document that cannot be used directly– Entity references

• Start with an ampersand (&) and finish with a semicolon (;)• There are five built-inentity references in XML

– Character references• Begin with &# and end with a semicolon (;)• Example: the Greek letter omega (Ω) as a reference it would

be &#x03A9; in hexadecimal or &#937; in decimal

Well-Formed XML – Entity and Character References

Well-Formed XML – Entity and Character References

<!DOCTYPE myElement [<!ENTITY copyright “© Wrox 2012”>

]>

Well-Formed XML – Elements Versus Attributes

Well-Formed XML – Elements Versus Attributes

Rule ????

Well-Formed XML – Elements Versus Attributes

Attributes• There is only one piece of

data• Names cannot be repeated• Make file size is smaller

– Good to sent across network

Elements• The data is not a simple

type• Items may need to be

repeated• Items can be ordered• A large amount of content

that is just text

Well-Formed XML – Elements Versus Attributes - Examples

Well-Formed XML – Elements Versus Attributes - Examples

Well-Formed XML – Processing Instructions

• is used to communicate with the application that is consuming the XML– It is not used directly by the XML parser at all

Well-Formed XML – CDATA

• These are used as a way to avoid repetitive escaping of characters

• Starts with <![CDATA[ and ends with ]]>• Example: you want data in your document

1 kilometer < 1 mile1 pint < 1 liter1 pound < 1 kilogram

Well-Formed XML – CDATA

Well-Formed XML – CDATA

• A common use of CDATA is in XHTML, the XML version of HTML

Well-Formed XML – CDATA

• A common use of CDATA is in XHTML, the XML version of HTML

Well-Formed XML – Exercise

XML Namespaces – Example

You need a new table

Dining table

Database table

HTML table

XML Namespaces

• A way of grouping elements and attributes under a common heading in order to differentiate them from similarly-named items

XML Namespaces – Example

XML Namespaces – Example

XML Namespaces – Why do you need namespaces?

• You won’t always be using own XML formats entirely within your own systems

XML Namespaces – How do you choose a namespace?

• In Java, are called packages• In C#, are called namespaces– System.Windows.Forms.Timer– System.Timers.Timer– System.Threading.Timer

XML Namespaces – How do you choose a namespace?

• You can choose virtually any string of characters to make sure your element’s full name is unique

• W3C recommend– URIs

URLs, URIs, and URNs

• URL is a Uniform Resource Locator, tells you the how and where of something– [Scheme]://[Domain]:[Port]/[Path]?

[QueryString]#[FragmentId]– http://www.wrox.com/remtitle.cgi?isgn=0470114878

• URN is a Uniform Resource Name, is simply a unique name– urn:[namespace identifier]:[namespace specific string]– urn:isbn:9780470114872

• URI is a Uniform Resource Identifier, is URL or URN

XML Namespaces – How to declare a namespace?

• If you want all elements to be under the namespace– Declare a default namespace

XML Namespaces – How to declare a namespace?

• If you want specific elements to be under the namespace– Declare a namespace explicitly– Choose prefix to represent namespace• Some prefixes are reserved, such as xml, xmlns, and

any other combinations beginning with the characters xml

XML Namespaces – How to declare a namespace?

Qualified Name

(QName)Local Name

XML Namespaces – How to declare a namespace?

XML Namespaces – Declaring more than one namespace

• <applicationUsers> element belongs to http://wrox.com/namespaces/applications/hr/config namespace

• <user> elements belong to http://wrox.com/namespaces/general/entities namespace

XML Namespaces – Declaring more than one namespace

XML Namespaces – Declaring more than one namespace

XML Namespaces

XML Namespaces – Real world

• XML Schemas– Defining the structure of a document

• Combination documents– Merging documents from more than one source

• Versioning– Differentiating between different versions of an

XML format

XML Namespaces – Combination documents

XML Namespaces – Versioning

• Differentiating between different versions of an XML format

• Go back to employees.xml– Namespace is

http://wrox.com/namespaces/general/employee– Newer version:

http://wrox.com/namespaces/general/employee/v2

XML Namespaces – Versioning

How do I want the application to handle the two different versions?

XML Namespaces – Versioning

• Version one of the application opens a version one file

• Version one of the application opens a version two file

• Version two of the application opens a version one file

• Version two of the application opens a version two file

XML Namespaces – Versioning – Practical

XML Namespaces – When to use and not use namespaces

When namespaces are needed

• When there’s no choice• When you need

interoperability• When you need validation

When namespaces are not needed

• When you have the need to store or exchange data for relatively small documents that will be seen only by a limited number of systems

XML Namespaces – Common namespaces

• The XML Namespacehttp://www.w3.org/XML/1998/namespace– Attributes:• xml:lang• xml:space• xml:base• xml:id• xml:Father

XML Namespaces – Common namespaces

• The XMLNS Namespacehttp://www.w3.org/2000/xmlns/

• The XML Schema Namespacehttp://www.w3.org/2001/XMLSchema

• The XSLT Namespace (xsl or xslt)http://www.w3.org/1999/XSL/Transform

• The SOAP Namespace (soap, soap12)http://schemas.xmlsoap.org/soap/envelope/ (SOAP 1.1)http://www.w3.org/2003/05/soap-envelope (SOAP 1.2)

• The WSDL Namespace (wsdl)http://www.w3.org/ns/wsdl (1.0, 2.0)

XML Namespaces – Common namespaces

• The Atom Namespacehttp://www.w3.org/2005/Atom

• The MathML Namespacehttp://www.w3.org/1998/Math/MathML

• The Docbook Namespacehttp://docbook.org/ns/docbook

XML Namespaces – Exercise