comp2513 xml – extensible markup language

Comp2513Comp2513

XML – eXtensible Markup XML – eXtensible Markup LanguageLanguage

Daniel L. Silver, Ph.D.Daniel L. Silver, Ph.D.

2002 Daniel L. Silver 2

ObjectivesObjectives

To discuss problems with the HTML based To discuss problems with the HTML based web and introduce XML (and related web and introduce XML (and related methods) as the next generation markup methods) as the next generation markup language language

References: DDEA Ch. 8, Sharma Ch.7 and References: DDEA Ch. 8, Sharma Ch.7 and External Web LinksExternal Web Links


OutlineOutline

Problems with the HTML based WebProblems with the HTML based Web The XML ideaThe XML idea XML fundamentalsXML fundamentals XML useXML use


Problems with Problems with the HTML based Webthe HTML based Web

HTML documents focus on display and not HTML documents focus on display and not structure and meaning of data - an information structure and meaning of data - an information maze devoid of meaningmaze devoid of meaning

Inefficient use of tags (every instance of data must Inefficient use of tags (every instance of data must be tagged)be tagged)

Fixed number of tags - can not be extended (not Fixed number of tags - can not be extended (not extensible)extensible)

HTML search is based on keywords without HTML search is based on keywords without contextcontext

Client-server applications cannot easily exchange Client-server applications cannot easily exchange data using HTMLdata using HTML


HTML focuses on display syntaxHTML focuses on display syntax

HTML tags such as <B>Simpson<\B> tell HTML tags such as <B>Simpson<\B> tell how to display the word “Simpson”how to display the word “Simpson”

Focus is on presentation (format, syntax)Focus is on presentation (format, syntax) But its does not define what But its does not define what “Simpson”“Simpson” means means

– A persons name? A city? A company?A persons name? A city? A company? Or its structural relationship to other dataOr its structural relationship to other data

– Full name? Last name? First name?Full name? Last name? First name?


The XML ideaThe XML idea

eXtensible Markup LanguageeXtensible Markup Language XML defines meaning (semantics): XML defines meaning (semantics):

<lname>Simpson<\lname><lname>Simpson<\lname> In terms of structural relationships …In terms of structural relationships … Independent of Independent of

presentationpresentation<mail_adrs> <fname>Homer<\fname> <lname>Simpson<\lname> <strnum>1234<\strnum> <str>Hickup Lane<\str><\mail_adrs>


What is XML?What is XML?

1996 - A simplified form of SGML for the web 1996 - A simplified form of SGML for the web (Standardized General Markup Language) (Standardized General Markup Language)

Both machine and human readableBoth machine and human readable Separates content, structure Separates content, structure

and presentationand presentation Extensible (users can define structure and Extensible (users can define structure and

meaning)meaning) Supports information reuse and processing Supports information reuse and processing

autonomy (application decides how to use/present)autonomy (application decides how to use/present)

SGML

HTMLXML


The W3C’s Basic Requirements for The W3C’s Basic Requirements for XMLXML

XML shall be straightforwardly usable over the Internet.XML shall be straightforwardly usable over the Internet. XML shall support a wide variety of applications.XML shall support a wide variety of applications. XML shall be compatible with SGML.XML shall be compatible with SGML. It shall be easy to write programs which process XML It shall be easy to write programs which process XML

documents.documents. The number of optional features in XML is to be kept to The number of optional features in XML is to be kept to

the absolute minimum, ideally zero.the absolute minimum, ideally zero. XML documents should be human-legible and XML documents should be human-legible and

reasonably clear.reasonably clear. XML documents should be easy to prepare.XML documents should be easy to prepare. The design of XML shall be formal and concise.The design of XML shall be formal and concise. Terseness in XML markup is of minimal importance.Terseness in XML markup is of minimal importance.


XML FundamentalsXML Fundamentals<?xml version = "1.0"?>…<contacts> <contact> <LastName>Black</LastName> <FirstName>John</FirstName> </contact> …</contacts>

XML Content

<?xml version="1.0"?><xsl:stylesheet xmlns:xsl = "http://www.w3.org/TR/WD-xsl">…

<!ELEMENT contacts (contact)* ><!ELEMENT contact (LastName, FirstName) ><!ELEMENT LastName (#PCDATA) ><!ELEMENT FirstName (#PCDATA) >

Presentationin Context

XSL Presentation

DTD Structure


XML’s Intended UseXML’s Intended Use

Standard format for exchanging dataStandard format for exchanging data Promote cross-platform and cross-application Promote cross-platform and cross-application

schema – independent of data content, use and schema – independent of data content, use and presentationpresentation

Oriented toward giving meaning to data, and does Oriented toward giving meaning to data, and does not emphasize display issuesnot emphasize display issues

Client – describes valid data for displayClient – describes valid data for display Server – describes valid data for exchangeServer – describes valid data for exchange


XMLs Intended UseXMLs Intended Use

Allows organizations to maintain proprietary Allows organizations to maintain proprietary databases while at the same time communicate databases while at the same time communicate information with one anotherinformation with one another

Schemas for specific domains have been created:Schemas for specific domains have been created:– MusicMusic

– Chemical symbols Chemical symbols

– Mathematical formulasMathematical formulas

– Common industry models (EDI for B2B)Common industry models (EDI for B2B)

– Web resource descriptions (directories, addresses)Web resource descriptions (directories, addresses)


XML versus HTMLXML versus HTML

XML is not a replacement for HTMLXML is not a replacement for HTML XML and HTML were designed with XML and HTML were designed with

different goals:different goals:– HTML was designed to display data and to HTML was designed to display data and to

focus on how data looksfocus on how data looks– XML was designed to describe data and to XML was designed to describe data and to

focus on what data meansfocus on what data means They complement each otherThey complement each other


XML eXtensibilityXML eXtensibility

XML allows you to create your own XML allows you to create your own definitions of data and there relationship to definitions of data and there relationship to other pieces of dataother pieces of data

Thus the nameThus the name

eXtensibleeXtensible ** Note that XML is ** Note that XML is

case sensitive **case sensitive **

<?xml version="1.0"?> <People> <Person> <Name> <First>Patrick</First> <Last>Joe</Last> </Name> </Person></People>


Using IE to Explore XMLUsing IE to Explore XML

You can use Internet Explorer to view an You can use Internet Explorer to view an XML document directlyXML document directly

A plus (+) or minus sign (-) to the left of the A plus (+) or minus sign (-) to the left of the XML elements can be clicked to expand or XML elements can be clicked to expand or collapse the element structurecollapse the element structure

Or view the raw XML source using "View Or view the raw XML source using "View Source" from the browser menuSource" from the browser menu

Example: Example: cd_catalog.xmlcd_catalog.xml


Defining XML StructureDefining XML Structure

DTD – DTD – Document Type DefinitionDocument Type Definition defines defines the fields in an XML document and their the fields in an XML document and their relation to one another (schema)relation to one another (schema)

Meta-data : data about dataMeta-data : data about data Can be included in .xml fileCan be included in .xml file or or

referenced as a .dtd filereferenced as a .dtd file Used by applications to Used by applications to

validate XML data validate XML data

<!ELMENT People (Person)* ><!ELMENT Person (Name) ><!ELMENT Name (First, Last) ><!ELMENT First (#PCDATA) ><!ELMENT Last (#PCDATA) >


Processing an XML DocumentProcessing an XML Document<?xml version="1.0"?> <People> <Person> <Name> <First>Patrick</First> <Last>Joe</Last> </Name> </Person></People>

<!ELMENT People (Person)* ><!ELMENT Person (Name) ><!ELMENT Name (First, Last) ><!ELMENT First (#PCDATA) ><!ELMENT Last (#PCDATA) >

DTD Structure

XML Content An application that wishes to use XMLdata should parse the data using a DTD.There are two approaches:•DOM – read the entire document using the DTD and build a tree of elements•SAX – parse on demand (interactively) as each new element is encountered

DOM = Document Object ModelSAX = Simple API for XML


Processing an XML DocumentProcessing an XML Document

Internet Explorer 5.0 (+) has a built in Internet Explorer 5.0 (+) has a built in DOM-based XML parser, DOM-based XML parser, msxml msxml

DTD can be embedded in XML or DTD can be embedded in XML or referencedreferenced

Examples:Examples:– simple_example.xmlsimple_example.xml with DTD embedded with DTD embedded– letter.xml letter.xml and and letter.dtdletter.dtd


Displaying XML DocumentsDisplaying XML Documents

Can be accomplished in various ways, any Can be accomplished in various ways, any program that can parse the XML can program that can parse the XML can display the informationdisplay the information

Here is a simple HTML solution …Here is a simple HTML solution …– simple_contact.htmlsimple_contact.html - XML is embedded, DTD - XML is embedded, DTD

is not requiredis not required Javascript could be used insteadJavascript could be used instead

– article.xmlarticle.xml and and DOMexample.htmlDOMexample.html– note.xml note.xml and and note.htmlnote.html


Displaying XML DocumentsDisplaying XML Documents

An XSL – eXtensible Stylesheet Layout can An XSL – eXtensible Stylesheet Layout can be usedbe used

Examples:Examples:Basic - Basic - contact3.xml using contact_list3.xslcontact3.xml using contact_list3.xsl

Full function – Full function – contact.xmlcontact.xml using contact_list.xsl using contact_list.xsl

Handheld – Handheld – contact2.xml using contact_list2.xslcontact2.xml using contact_list2.xsl

<?xml version="1.0"?><xsl:stylesheet xmlns:xsl = "http://www.w3.org/TR/WD-xsl">…


Transferring Data with XMLTransferring Data with XML

It is possible to use XML as a method of It is possible to use XML as a method of transferring meaningful data between transferring meaningful data between applications even when application applications even when application databases do not matchdatabases do not match

Adherence to XML DTD is the keyAdherence to XML DTD is the key

App A App BDB2 Oracle

JDBC ODBCXML

Common DTD


Smart Searches on the InternetSmart Searches on the Internet

With XML and DTDs, keyword searches on With XML and DTDs, keyword searches on the Internet can now be aimed at the the Internet can now be aimed at the appropriate systems, databases, pagesappropriate systems, databases, pages

A syntactic search using IE: A syntactic search using IE: ““cook New York kitchen restaurant”cook New York kitchen restaurant”

… … would become …would become … A semantic search: A semantic search:

<occupation>cook</occupation><occupation>cook</occupation><city>New York</city><city>New York</city>


VXMLVXML

Voice XMLVoice XML Sound embedded as content and processed Sound embedded as content and processed

as per style sheetas per style sheet Other media types will be used as well Other media types will be used as well


eadmin and XMLeadmin and XML

EadminEadmin load.jsp?id=91load.jsp?id=91 servlet/LoadStoreservlet/LoadStore StoreLoader(store,xmlfile)StoreLoader(store,xmlfile)

store.xml store.dtd


ReferencesReferences

http://www.w3.org/XML/http://www.w3.org/XML/ http://www.xmlfiles.com/xml/http://www.xmlfiles.com/xml/

THE ENDTHE END

[email protected]@acadiau.ca


XMLXML

eXtensible Markup LanguageeXtensible Markup Language HTML tags such as <B>Silver<\B> tell HTML tags such as <B>Silver<\B> tell

how to display the word “Silver”how to display the word “Silver” But its does not define what it meansBut its does not define what it means XML defines meaning: XML defines meaning:

<last_name>Silver<\last_name><last_name>Silver<\last_name> And to create structure …And to create structure …


Major Architectural Components Major Architectural Components of the Webof the Web

InternetInternet

Browser

DatabaseServer

Client 1

Server A

Server BBank

Server

URL

HTTPTCP/IP

Browser

Client 2 HTTPServer

App.Server

index.html

BankServer

Dedicated

prog.cgi