Introduction to XML

Introduction to XML

Kostas KontogiannisEvan Mamas

OutlineIntroduce XML, HTML and SGMLCompare and Contrast

XML vs. HTML XML vs. SGML

XML Components, Applications, Industry

Thoughts on XML

What is XML?eXtensible Markup Language

Proper subset of SGML for web use

Meta-language Allows you to create your own markup languages

Compromise between HTML and SGML

What is HTML ?HyperText Markup LanguageLanguage to describe information for

transmission over the web.Uses tags to markup the informationTags are just a formatting toolExample

<H1> Hello, World </H1> Hello, World

Why isn’t HTML enough?Good enough for presenting text on the

webNot accepted as an authoring or archival

formExtensibility

HTML standard changes continually Uses tags for formatting

Structures Has no defined or definable structural rules

What is SGML ?Standard Generalized Markup Language

International Standard for over 10 yearsLanguage for specifying markup

languagesDescribes only the formal properties and

inter-relations of the components of a document

Document, Entities, Elements, Attributes

Uses of SGMLFormally structured documents

Technical ManualsExchange documents

Product documentationData encodingInterchange specificationProvide long-term storage of information

which was independent of suppliers and changes in h/w and s/w

SGML ExampleMemo

DTD (Document Type Definition)

<to>All staff<from>Martin Bryan<date>5th November<subject>Cats and Dogs<text>Please remember to keep all cats and dogs indoors tonight.

<!DOCTYPE memo [<!ELEMENT memo O O ((to & from & date & subject?), text) ><!ELEMENT text - O (para+) ><!ELEMENT para O O (#PCDATA) ><!ELEMENT (to, from, date, subject) - O (#PCDATA) >]>

Why isn’t SGML enough?Specification is very longContains many options not needed for

Web applicationsTime consuming and high cost

Expensive toolsToo much for small applicationsBad reputation

XML vs. HTMLNew tags and attributes definitions

allowedDocument structures can be nested

to any level of complexityStructural validation is possible by

describing the grammar

XML vs. SGMLXML is the minimum required subset

of SGML for web useEasier to implement and to create

tools forA new attempt at structured markup

languages with a new “face”

XML Components XML Style Language (XSL) Cascading Style Sheets, level 2 CCS2 XML Document Object Model (DOM) XML Linking Language (XLL) XML Pointer Language (XPL) XML Name Spaces Synchronized Multimedia Integration Language

(SMIL) Resource Description Framework (RDF) Mathematical Markup Language (MathML)

XML Components (cont.)

XML Style Language (XSL) Defines a way to present the documents Separates formatting from content Has two steps:

Generate a result tree (associate patterns with templates) Use XML Namespace (formatting vocabulary) to generate

formatted output. Similar to DSSSL for SGML

XML Components (cont.) Cascading Style Sheets, level 2 CCS2

Defines a way to present documents Similar to XSL (Not as strong) Supported by most browsers

<HTML> <TITLE>Bach's home page</TITLE> <STYLE type="text/css"> H1 { color: blue } </STYLE> <BODY> <H1>Bach's home page</H1> <P>Johann Sebastian Bach was a prolific composer. </BODY> </HTML>

XML Components (cont.)

XML Document Object Model (DOM) In-memory model for representing parsed XML

documents Designed to provide common structures in XML

browsers Intended to enable interoperable XML processing across

browsers Implemented by Internet Explorer and Netscape

XML Components (cont.) XML Linking Language (XLL)

Links by reference rather than exact location Provides hyperlinking elements

Simple links like HTML links Extended

• Multi-directional links• Links with multiple destinations• Placing content inline from a linked document

Requires use of XML Pointer Language

XML Components (cont.) XML Name Spaces

Vocabulary of all elements and attribute types Namespace prefix (mapped to Uniform Redource

Identifier) Local Part

Allows use of names defined in other documents Modularity and reuse of a markup Mechanisms to establish name scope

XML Components (cont.) Synchronized Multimedia Integration Language (SMIL)

Language for describing interactive synchronized multimedia distributed on the Web

Several components (images, video, audio) can be linked together to create a presentation on the web

Resource Description Framework (RDF) Abstract mechanism for defining simple relationships among

web resources

Mathematical Markup Language (MathML) Language to describe mathematical expressions

XML DTDDefines the hierarchy of all user-

defined elements (tags) in the XML document

Declares the attributes and behaviour of each XML element

Each XML document calls a specific DTD file to validate its elements

XML DTD <?xml version="1.0" encoding="UTF-8"?> 



<!ELEMENT Language (FileTag*,Declaration*,Function_Call*)> <!ELEMENT FileTag (IncludeTag*,SourceTag*)> <!ELEMENT IncludeTag (#PCDATA)*> <!ELEMENT SourceTag (#PCDATA)*>

<!ELEMENT Declaration (Type_Name|Identifier)*> <!ELEMENT Type_Name (#PCDATA)*> <!ELEMENT Identifier (#PCDATA)*>

<!ELEMENT Function_Call (Return_Type*,Function_Name*,Argument*)> <!ELEMENT Return_Type (Return_Var*)> <!ELEMENT Return_Var (#PCDATA)>

<!ELEMENT Function_Name (#PCDATA)> <!ELEMENT Argument (parameterName*)> <!ELEMENT parameterName (#PCDATA)>  <!ELEMENT External_Call EMPTY> <!ELEMENT Graphics EMPTY>



Defines what other tags are within the <Language> tagDefines data types for contents within the <IncludeTag> tag

XML Document (page 1 of 2)

<?xml version="1.0"?> <?xml:stylesheet type="text/xsl" href="studentXSL1.xsl" ?> <!DOCTYPE Language SYSTEM "Student.dtd"> <Language> <FileTag> <IncludeTag>include stdio.h:</IncludeTag> </FileTag> <FileTag> <IncludeTag>include math.h</IncludeTag> </FileTag> <FileTag> <SourceTag>code statement3:</SourceTag> </FileTag> <FileTag> <SourceTag>code statement2:</SourceTag> </FileTag>

<Declaration> <Type_Name>char*</Type_Name> <Identifier>UW</Identifier> </Declaration>

Calls a XSL style sheetCalls a DTD document

XML Document (page 2 of 2)

<Declaration> <Type_Name>int</Type_Name> <Identifier>numOfstudents</Identifier> </Declaration>

<Declaration> <Type_Name>char*</Type_Name> <Identifier>facultyName</Identifier> </Declaration>

<Function_Call> <Return_Type> <Return_Var>student_profile</Return_Var> </Return_Type> <Function_Name>elec_eng</Function_Name> <Argument> <parameterName>name</parameterName> </Argument> </Function_Call> </Language>

XML NamespacesLatest milestone for W3C's XML

technology (14-January-1999 ) W3C’s definition of XML NameSpaces:

“XML namespaces provide a simple method for qualifying element and attribute names used in Extensible Markup Language documents by associating them with namespaces identified by URI references.”

Why use it?Maintain tag meaningfulness and uniqueness

How does it solve the problem?Add context to XML tags by using prefix and URL

XSL Document (Page 1 of 3)

<?xml version="1.0"?> <DIV xmlns:xsl="http://www.w3.org/TR/WD-xsl"> <html:html xmlns:html="http://www.w3.org/TR/REC-html40"> <i>This page consists of XML, XSL, Namespace, HTML, and Java Applet</i> <html:head><html:title><H1>Sample C Code (hidden XML tag)</H1></html:title></html:head> <xsl:for-each select="Language"> <TD STYLE="padding-left:1em"> <DIV><xsl:value-of select="/"/></DIV> <html:font color="red">The above command prints out all contents within tags without any

formmating, ordering, linebreaks, etc.</html:font> </TD> </xsl:for-each>

<xsl:for-each order-by="+ IncludeTag" select="Language/FileTag"> <TD STYLE="padding-left:1em"> <html:BR></html:BR> <DIV><html:BR><xsl:value-of select="IncludeTag"/></html:BR></DIV> </TD> </xsl:for-each> <html:font color="red">End of IncludeTag, ascending sort on Include Tag Content</html:font>

Namespace for XSLNamespace for HTML

XSL Document (Page 2 of 3)

<xsl:for-each order-by="+ SourceTag" select="Language/FileTag"> <TD STYLE="padding-left:1em"> <html:BR></html:BR> <DIV><xsl:value-of page-break-after="SourceTag" select="SourceTag"/></DIV> </TD> </xsl:for-each> <html:font color="red">End of SourceTag, ascending sort on SourceTag Content</html:font> <html:BR></html:BR> <xsl:for-each order-by="+ Type_Name" select="Language/Declaration"> <TD STYLE="padding-left:1em"> <html:BR></html:BR> <DIV><html:BR><xsl:value-of select="Type_Name"/></html:BR></DIV> <DIV><html:BR><xsl:value-of select="Identifier"/></html:BR></DIV> </TD> </xsl:for-each> <html:font color="red">End of Declaration, ascending sort on Type_Name</html:font> <DIV></DIV>

XSL Document (Page 3 of 3) <xsl:for-each select="Language/Function_Call"> <TD STYLE="padding-left:1em">

<html:BR><DIV><xsl:value-of select="Return_Type"/></DIV></html:BR> <html:font color="red">End of Return_Type</html:font> <html:BR><DIV><xsl:value-of select="Function_Name"/></DIV></html:BR> <html:font color="red">End of Function_Name</html:font> <html:BR></html:BR> <html:BR><DIV><xsl:value-of select="Argument"/></DIV></html:BR> <html:font color="red">End of Argument</html:font> <html:BR></html:BR> </TD> </xsl:for-each> <html:BR></html:BR>

<html:APPLET code="AgentAction.class" width="400" height="200"></html:APPLET> <html:BR></html:BR> </html:html> </DIV>

Applications that require XMLInformation exchange between

heterogeneous databases Health care example

Distributed processing Semiconductor industry example

Multiple views of the same data“Intelligent” information agents

Using XMLXML for Storage

Compact syntax Generalized and standarized Product independent

XML for Searching Use of content specific markup enables robust

searching Search engines need to be XML aware Can use current SGML search engines

What is DOM?A programming API for XMLlogical structure of documentAccess and Manipulation of

documents

What is DOM?As an object model, DOM identifies

Interface and Objects used for the doc.

Behaviours and Attributes Relationships and Collaborations of

Interfaces and Objects

What is DOM?2 Major Components for DOM Level 1

DOM Core = Basic functionalities for XML

DOM HTML = Objects and Methods specific to HTML

Level 2 DOM CSS, DOM Event, DOM Filters and

Iterators, DOM Range

Advantages of using DOMEasy to create, navigate, add,

modify documentsDOM abstraction avoids

implementation dependenciesDOM applications may use

additional language bindings

A Typical DOM Structure<condition_statement>

<if_statement><if_tag> if </if_tag>

<expression_tag> (b == c) </expression_tag><statement_tag> {a += c} </statement_tag>

</if_statement>

</condition_statement>

A Typical DOM Structure (2)

<if_statements>

<if_tag>> <statement_tag><expression_tag>

<condition_statements>

if (b==c) {a+=c}

A Typical DOM Structure (3)DOM abstraction is a Tree or Forest

StructureUsers have full flexibility to specify

the structureStructural Isomorphism

Some Key ObjectsNode

Tree node of the document root node, parents and children

Element (is a Node object) Elements of a document Represents contents between the start

tag and end tag Attributes: defined by DTD

Some Key Objects (2)Document

root node of a documentNodeIterator

iterates over a set of nodes specified by a filter

AttributeList collection of Attribute objects, indexed

by attribute name

Some Key Objects (3)Attribute

attribute of an Element ObjectDocumentContext

respository for metadata about a document

DOM provides instance-independent

document operations

Memory Management for DOMDOM APIs operate across a variety of

memory implementation methods: Language platforms that do not expose

memory management to user Language (Java) that provides

constructors with Garbage collection capability

Language (C/C++) that requires explicit memory allocations

Resources/Quirks IE 5 and Navigator 5.0 implement

different features:IE 5.0 - XML/XSL Navigator - XML/CSSNavigator to support RDF

XML Resources:http://www.swen.uwaterloo.ca/~group1

Using XML (cont.)XML for Presentation

Convert to HTML at server Use Java applications to render in browser

Slow Use XSL or CSS to render in browser

Fast

XML in the industry

Explosive growth of XML tools and specifications Tools: JADE, MSXML, JUMBO,... Specifications: CDF, CFML,EDI Browsers: IE, Netscape

Thoughts on XMLSeems like a transition stage between

HTML and SGML Will we eventually end up using SGML?

XML follows basic principles of SE Higher abstraction layer Reuse Modularity

References XML.COM - A guide to XML

http://www.xml.com/xml/pub/w3j/s3.walsh.html XML.COM - The Road to XML: Adapting SGML to the Web

http://www.xml.com/xml/pub/w3j/s1.discussion.html The Computer Bulletin - The XML Files

http://www.bcs.org.uk/publicat/ebull/may98/xml.htm XML, Java, and the future of the Web

http://sunsite.unc.edu/pub/sun-info/standards/xml/why/xmlapps.htm XML: What is it

http://iai.sgml.com/980106-01.asp Why do we need XML?

http://info.admin.kth.se/SGML/Konferenser/xml98sve/seminar.html An Introduction to the Standard Generalized Markup Language

http://www.personal.u-net.com/~sgml/sgml.htm SGML101

http://www.uslynx.com/sgml101.htm

Documents

Introduction to XML