XML 4 Beginners by Pratap

7/31/2019 XML 4 Beginners by Pratap

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XML 4 BEGINNERSXML 4 BEGINNERS-- PRATAP ---- PRATAP --


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XMLXML TutorialTutorial

XML stands for eXML stands for eXXtensibletensible MMarkuparkup LLanguage.anguage. XML is designed to transport and store data.XML is designed to transport and store data. XML is important to know, and very easy to learn.XML is important to know, and very easy to learn.


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Introduction toIntroduction to XMLXML

XML was designed to transport and store data.XML was designed to transport and store data. HTML was designed to display data.HTML was designed to display data.

What You Should Already KnowWhat You Should Already KnowBefore you continue you should have a basicBefore you continue you should have a basic

understanding of the following:understanding of the following: HTMLHTML

JavaScriptJavaScript


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What is XML?What is XML?

XML stands for EXtensible Markup LanguageXML stands for EXtensible Markup Language XML is a markup language much like HTMLXML is a markup language much like HTML XML was designed to carry data, not to displayXML was designed to carry data, not to display

datadata XML tags are not predefined. You must define yourXML tags are not predefined. You must define your

own tagsown tags XML is designed to be self-descriptiveXML is designed to be self-descriptive

XML is a W3C RecommendationXML is a W3C Recommendation


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The Difference Between XMLThe Difference Between XMLand HTMLand HTML

XML is not a replacement for HTML.XML is not a replacement for HTML. XML and HTML were designed with different goals:XML and HTML were designed with different goals: XML was designed to transport and store data,XML was designed to transport and store data,

with focus on what data iswith focus on what data is HTML was designed to display data, with focus onHTML was designed to display data, with focus on

how data lookshow data looks HTML is about displaying information, while XML isHTML is about displaying information, while XML is

about carrying information.about carrying information.


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XML Does Not DO AnythingXML Does Not DO Anything

Maybe it is a little hard to understand, but XMLMaybe it is a little hard to understand, but XMLdoes not DO anything. XML was created todoes not DO anything. XML was created tostructure, store, and transport information.structure, store, and transport information.

The following example is a note to Tove, from Jani,The following example is a note to Tove, from Jani,

stored as XML:stored as XML:

ToveTove

JaniJaniReminderReminderDon't forget me this weekend!Don't forget me this weekend!


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The note above is quite self descriptive. It hasThe note above is quite self descriptive. It hassender and receiver information, it also has asender and receiver information, it also has aheading and a message body.heading and a message body.

But still, this XML document does not DO anything.But still, this XML document does not DO anything.It is just information wrapped in tags. SomeoneIt is just information wrapped in tags. Someonemust write a piece of software to send, receive ormust write a piece of software to send, receive ordisplay it.display it.


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With XML You Invent Your OwnWith XML You Invent Your OwnTagsTags

The tags in the example above (like andThe tags in the example above (like and) are not defined in any XML standard.) are not defined in any XML standard.

These tags are "invented" by the author of theThese tags are "invented" by the author of theXML document.XML document.

That is because the XML language has noThat is because the XML language has nopredefined tags.predefined tags.

The tags used in HTML are predefined. HTMLThe tags used in HTML are predefined. HTMLdocuments can only use tags defined in the HTMLdocuments can only use tags defined in the HTML

standard (like

, , etc.).standard (like

, , etc.). XML allows the author to define his/her own tagsXML allows the author to define his/her own tags

and his/her own document structure.and his/her own document structure.


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XML is Not a Replacement forXML is Not a Replacement forHTMLHTML

XML is a complement to HTML.XML is a complement to HTML.

It is important to understand that XML is not aIt is important to understand that XML is not areplacement for HTML. In most web applications,replacement for HTML. In most web applications,

XML is used to transport data, while HTML is usedXML is used to transport data, while HTML is usedto format and display the data.to format and display the data.

My best description of XML is this:My best description of XML is this:

XML is a software- and hardware-XML is a software- and hardware-independent tool for carrying information.independent tool for carrying information.

XML is a W3C RecommendationXML is a W3C Recommendation

XML became a W3C Recommendation onXML became a W3C Recommendation onFebruar 10 1998.Februar 10, 1998.


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XML is EverywhereXML is Everywhere XML is now as important for the Web asXML is now as important for the Web as

HTML was to the foundation of the Web.HTML was to the foundation of the Web.

XML is the most common tool for dataXML is the most common tool for datatransmissions between all sorts oftransmissions between all sorts of

applications.applications.


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How Can XML beHow Can XML be Used?Used?

XML is used in many aspects of web development,XML is used in many aspects of web development,often to simplify data storage and sharing.often to simplify data storage and sharing.

XML Separates Data from HTMLXML Separates Data from HTML If you need to display dynamic data in your HTMLIf you need to display dynamic data in your HTML

document, it will take a lot of work to edit the HTML eachdocument, it will take a lot of work to edit the HTML eachtime the data changes.time the data changes.

With XML, data can be stored in separate XML files. ThisWith XML, data can be stored in separate XML files. This

way you can concentrate on using HTML/CSS for displayway you can concentrate on using HTML/CSS for displayand layout, and be sure that changes in the underlyingand layout, and be sure that changes in the underlyingdata will not require any changes to the HTML.data will not require any changes to the HTML.

With a few lines of JavaScript code, you can read anWith a few lines of JavaScript code, you can read anexternal XML file and update the data content of yourexternal XML file and update the data content of your

web page.web page.


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XML Simplifies Data SharingXML Simplifies Data Sharing

In the real world, computer systems andIn the real world, computer systems anddatabases contain data in incompatible formats.databases contain data in incompatible formats.

XML data is stored in plain text format. ThisXML data is stored in plain text format. Thisprovides a software- and hardware-independentprovides a software- and hardware-independentway of storing data.way of storing data.

This makes it much easier to create data that canThis makes it much easier to create data that canbe shared by different applications.be shared by different applications.


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XML Simplifies DataXML Simplifies DataTransportTransport

One of the most time-consuming challenges forOne of the most time-consuming challenges fordevelopers is to exchange data betweendevelopers is to exchange data betweenincompatible systems over the Internet.incompatible systems over the Internet.

Exchanging data as XML greatly reduces thisExchanging data as XML greatly reduces thiscomplexity, since the data can be read by differentcomplexity, since the data can be read by differentincompatible applications.incompatible applications.


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XML Simplifies PlatformXML Simplifies PlatformChangesChanges

Upgrading to new systems (hardware or softwareUpgrading to new systems (hardware or softwareplatforms), is always time consuming. Largeplatforms), is always time consuming. Largeamounts of data must be converted andamounts of data must be converted andincompatible data is often lost.incompatible data is often lost.

XML data is stored in text format. This makes itXML data is stored in text format. This makes iteasier to expand or upgrade to new operatingeasier to expand or upgrade to new operatingsystems, new applications, or new browsers,systems, new applications, or new browsers,without losing data.without losing data.


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XML Makes Your Data MoreXML Makes Your Data MoreAvailableAvailable

Different applications can access your data, notDifferent applications can access your data, notonly in HTML pages, but also from XML dataonly in HTML pages, but also from XML datasources.sources.

With XML, your data can be available to all kinds ofWith XML, your data can be available to all kinds of"reading machines" (Handheld computers, voice"reading machines" (Handheld computers, voicemachines, news feeds, etc), and make it moremachines, news feeds, etc), and make it moreavailable for blind people, or people with otheravailable for blind people, or people with otherdisabilities.disabilities.


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XML is Used to Create NewXML is Used to Create NewInternet LanguagesInternet Languages

A lot of new Internet languages are created with XML.A lot of new Internet languages are created with XML. Here are some examples:Here are some examples: XHTMLXHTML WSDL for describing available web servicesWSDL for describing available web services WAP and WML as markup languages for handheld devicesWAP and WML as markup languages for handheld devices RSS languages for news feedsRSS languages for news feeds RDF and OWL for describing resources and ontologyRDF and OWL for describing resources and ontology SMIL for describing multimedia for the webSMIL for describing multimedia for the web

If Developers Have SenseIf Developers Have Sense

If they DO have sense, future applications willIf they DO have sense, future applications willexchange their data in XML.exchange their data in XML.

The future might give us word processors, spreadsheetThe future might give us word processors, spreadsheetapplications and databases that can read each other's dataapplications and databases that can read each other's datain XML format, without any conversion utilities in between.in XML format, without any conversion utilities in between.


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XMLXMLTreeTree

XML documents form a tree structure that starts at "theXML documents form a tree structure that starts at "theroot" and branches to "the leaves".root" and branches to "the leaves".

An Example XML DocumentAn Example XML Document

XML documents use a self-describing and simple syntax:XML documents use a self-describing and simple syntax:

ToveTove

JaniJaniReminderReminderDon't forget me this weekend!Don't forget me this weekend!


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The first line is the XML declaration. It defines the XML versionThe first line is the XML declaration. It defines the XML version(1.0) and the encoding used (ISO-8859-1 = Latin-1/West(1.0) and the encoding used (ISO-8859-1 = Latin-1/WestEuropean character set).European character set).

The next line describes theThe next line describes the root elementroot element of the documentof the document(like saying: "this document is a note"):(like saying: "this document is a note"):

The next 4 lines describe 4The next 4 lines describe 4 child elementschild elements of the root (to,of the root (to,from, heading, and body):from, heading, and body):

ToveToveJaniJaniReminderReminderDon't forget me this weekend!Don't forget me this weekend!


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And finally the last line defines the end of the rootAnd finally the last line defines the end of the rootelement:element:

You can assume, from this example, that the XMLYou can assume, from this example, that the XMLdocument contains a note to Tove from Jani.document contains a note to Tove from Jani.

Don't you agree that XML is pretty self-descriptive?Don't you agree that XML is pretty self-descriptive?


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XML Documents Form a TreeXML Documents Form a TreeStructureStructure

XML documents must contain aXML documents must contain a root elementroot element..This element is "the parent" of all other elements.This element is "the parent" of all other elements.The elements in an XML document form aThe elements in an XML document form a

document tree. The tree starts at the root anddocument tree. The tree starts at the root andbranches to the lowest level of the tree.branches to the lowest level of the tree.

All elements can have sub elements (childAll elements can have sub elements (childelements):elements):

..........


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The terms parent, child, and sibling are used toThe terms parent, child, and sibling are used todescribe the relationships between elements.describe the relationships between elements.Parent elements have children. Children on theParent elements have children. Children on the

same level are called siblings (brothers or sisters).same level are called siblings (brothers or sisters). All elements can have text content and attributesAll elements can have text content and attributes

(just like in HTML).(just like in HTML).


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The image above represents one book in the XML below:The image above represents one book in the XML below:

Everyday ItalianEveryday ItalianGiada De LaurentiisGiada De Laurentiis2005200530.0030.00

Harry PotterHarry Potter

J K. RowlingJ K. Rowling2005200529.9929.99

Learning XMLLearning XMLErik T. RayErik T. Ray2003200339.9539.95


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The root element in the example is .The root element in the example is .All elements in the document areAll elements in the document arecontained within .contained within .

The element has 4 children: ,, , .author>, , .


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XMLXML Syntax RulesSyntax Rules

The syntax rules of XML are very simple andThe syntax rules of XML are very simple andlogical. The rules are easy to learn, and easy tological. The rules are easy to learn, and easy touse.use.

All XML Elements Must Have a Closing TagAll XML Elements Must Have a Closing Tag In HTML, some elements do not have to have a closingIn HTML, some elements do not have to have a closing

tag:tag:

This is a paragraph.

This is a paragraph.

In XML, it is illegal to omit the closing tag. AllIn XML, it is illegal to omit the closing tag. Allelementselements mustmust have a closing tag:have a closing tag:


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NoteNote: You might have noticed from the previous: You might have noticed from the previousexample that the XML declaration did not have aexample that the XML declaration did not have aclosing tag. This is not an error. The declaration isclosing tag. This is not an error. The declaration isnot a part of the XML document itself, and it hasnot a part of the XML document itself, and it has

no closing tag.no closing tag.


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XML Tags are CaseXML Tags are CaseSensitiveSensitive

XML tags are case sensitive. The tag isXML tags are case sensitive. The tag isdifferent from the tag .different from the tag .

Opening and closing tags must be written with theOpening and closing tags must be written with thesame case:same case:

This is incorrectThis is incorrectThis is correct


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XML Elements Must be Properly NestedXML Elements Must be Properly Nested In HTML, you might see improperly nested elements:In HTML, you might see improperly nested elements:

This text is bold and italicThis text is bold and italic

In XML, all elementsIn XML, all elements mustmust be properly nested within each other:be properly nested within each other:

This text is bold and italicThis text is bold and italic

In the example above, "Properly nested" simply means thatIn the example above, "Properly nested" simply means that

since the element is opened inside the element, itsince the element is opened inside the element, itmust be closed inside the element.must be closed inside the element.

XML Documents Must Have a Root ElementXML Documents Must Have a Root Element XML documents must contain one element that is theXML documents must contain one element that is the

parentparent of all other elements. This element is called theof all other elements. This element is called the

rootroot element.element.

..........


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XML Attribute Values Must be QuotedXML Attribute Values Must be Quoted XML elements can have attributes in name/value pairsXML elements can have attributes in name/value pairsjust like in HTML.just like in HTML. In XML, the attribute values must always be quoted.In XML, the attribute values must always be quoted. Study the two XML documents below. The first one isStudy the two XML documents below. The first one is

incorrect, the second is correct:incorrect, the second is correct:

ToveToveJaniJani

ToveToveJaniJani

The error in the first document is that the dateThe error in the first document is that the dateattribute in the note element is not quoted.attribute in the note element is not quoted.


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Entity ReferencesEntity References

Some characters have a special meaning in XML.Some characters have a special meaning in XML.

If you place a character like "


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There are 5 predefined entity references in XML:There are 5 predefined entity references in XML:

Note:Note: Only the characters "


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Comments in XMLComments in XML

The syntax for writing comments in XML is similarThe syntax for writing comments in XML is similarto that of HTML.to that of HTML.

White-space is Preserved in XMLWhite-space is Preserved in XML HTML truncates multiple white-space characters to oneHTML truncates multiple white-space characters to one

single white-space:single white-space:


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XML Stores New Line as LFXML Stores New Line as LF

In Windows applications, a new line is normallyIn Windows applications, a new line is normallystored as a pair of characters: carriage return (CR)stored as a pair of characters: carriage return (CR)and line feed (LF). In Unix applications, a new lineand line feed (LF). In Unix applications, a new lineis normally stored as an LF character. Macintoshis normally stored as an LF character. Macintosh

applications also use an LF to store a new line.applications also use an LF to store a new line.

XML stores a new line as LF.XML stores a new line as LF.


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XMLXML ElementsElements

An XML document contains XML Elements.An XML document contains XML Elements.

What is an XML Element?What is an XML Element?

An XML element is everything from (including) theAn XML element is everything from (including) theelement's start tag to (including) the element's end tag.element's start tag to (including) the element's end tag.

An element can contain:An element can contain: other elementsother elements texttext attributesattributes or a mix of all of the above...or a mix of all of the above...


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Harry PotterHarry PotterJ K. RowlingJ K. Rowling2005200529.9929.99

Learning XMLLearning XMLErik T. RayErik T. Ray2003200339.9539.95

In the example above, and haveIn the example above, and have

element contentselement contents, because they contain other, because they contain otherelements. also has anelements. also has an attributeattribute(category="CHILDREN"). , , ,(category="CHILDREN"). , , ,

and haveand have text contenttext content because they containbecause they contain


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XML Naming RulesXML Naming Rules

XML elements must follow these naming rules:XML elements must follow these naming rules: Names can contain letters, numbers, and otherNames can contain letters, numbers, and other

characterscharacters Names cannot start with a number or punctuationNames cannot start with a number or punctuation

charactercharacter Names cannot start with the letters xml (or XML, or Xml,Names cannot start with the letters xml (or XML, or Xml,

etc)etc) Names cannot contain spacesNames cannot contain spaces

Any name can be used, no words are reserved.Any name can be used, no words are reserved.


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Best Naming PracticesBest Naming Practices Make names descriptive. Names with an underscoreMake names descriptive. Names with an underscore

separator are nice: , .separator are nice: , . Names should be short and simple, like this: Names should be short and simple, like this:

not like this: .not like this: . Avoid "-" characters. If you name something "first-name,"Avoid "-" characters. If you name something "first-name,"

some software may think you want to subtract name fromsome software may think you want to subtract name fromfirst.first.

Avoid "." characters. If you name something "first.name,"Avoid "." characters. If you name something "first.name,"some software may think that "name" is a property of thesome software may think that "name" is a property of theobject "first."object "first."

Avoid ":" characters. Colons are reserved to be used forAvoid ":" characters. Colons are reserved to be used forsomething called namespaces (more later).something called namespaces (more later).

XML documents often have a corresponding database. AXML documents often have a corresponding database. Agood practice is to use the naming rules of your databasegood practice is to use the naming rules of your databasefor the elements in the XML documents.for the elements in the XML documents.

Non-English letters like are perfectly legal in XML, butNon-English letters like are perfectly legal in XML, butwatch out for problems if your software vendor doesn'twatch out for problems if your software vendor doesn'tsupport them.support them.


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XML Elements areXML Elements areExtensibleExtensible

XML elements can be extended to carry moreXML elements can be extended to carry moreinformation.information. Look at the following XML example:Look at the following XML example:


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Imagine that the author of the XML document added someImagine that the author of the XML document added someextra information to it:extra information to it:

2008-01-102008-01-10ToveToveJaniJaniReminderReminderDon't forget me this weekend!Don't forget me this weekend!

Should the application break or crash?Should the application break or crash? No. The application should still be able to find the ,No. The application should still be able to find the ,

, and elements in the XML document and, and elements in the XML document andproduce the same output.produce the same output. One of the beauties of XML, is that it can be extendedOne of the beauties of XML, is that it can be extended

without breaking applications.without breaking applications.


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XMLXML AttributesAttributes

XML elements can have attributes, just like HTML.XML elements can have attributes, just like HTML. Attributes provide additional information about an element.Attributes provide additional information about an element.

XML AttributesXML Attributes In HTML, attributes provide additional information aboutIn HTML, attributes provide additional information about

elements:elements:

Attributes often provide information that is not a part of theAttributes often provide information that is not a part of the

data. In the example below, the file type is irrelevant to thedata. In the example below, the file type is irrelevant to thedata, but can be important to the software that wants todata, but can be important to the software that wants tomanipulate the element:manipulate the element:

computer.gifcomputer.gif

ib b


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XML Attributes Must beXML Attributes Must beQuotedQuoted

Attribute values must always be quoted. EitherAttribute values must always be quoted. Eithersingle or double quotes can be used. For asingle or double quotes can be used. For aperson's sex, the person element can be writtenperson's sex, the person element can be writtenlike this:like this:

or like this:or like this:


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If the attribute value itself contains double quotesIf the attribute value itself contains double quotesyou can use single quotes, like in this example:you can use single quotes, like in this example:

or you can use character entities:or you can use character entities:


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XML Elements vs. AttributesXML Elements vs. Attributes

Take a look at these examples:Take a look at these examples:

AnnaAnna

SmithSmith

femalefemale

AnnaAnnaSmithSmith


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In the first example sex is an attribute. In the last,In the first example sex is an attribute. In the last,sex is an element. Both examples provide thesex is an element. Both examples provide thesame information.same information.

There are no rules about when to use attributes orThere are no rules about when to use attributes or

when to use elements. Attributes are handy inwhen to use elements. Attributes are handy inHTML. In XML my advice is to avoid them. UseHTML. In XML my advice is to avoid them. Useelements instead.elements instead.


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My Favorite WayMy Favorite Way

The following three XML documents containThe following three XML documents containexactly the same information:exactly the same information:

A date attribute is used in the first example:A date attribute is used in the first example:

ToveToveJaniJaniReminderReminder

Don't forget me this weekend!Don't forget me this weekend!

d l i d i h d lA d t l t i d i th d l


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A date element is used in the second example:A date element is used in the second example:

10/01/200810/01/2008ToveToveJaniJaniReminderReminderDon't forget me this weekend!Don't forget me this weekend!

An expanded date element is used in the third: (THIS IS MYAn expanded date element is used in the third: (THIS IS MYFAVORITE):FAVORITE):

1010010120082008

ToveToveJaniJaniReminderReminderDon't forget me this weekend!Don't forget me this weekend!


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Avoid XML Attributes?Avoid XML Attributes?

Some of the problems with using attributes are:Some of the problems with using attributes are: attributes cannot contain multiple values (elements can)attributes cannot contain multiple values (elements can) attributes cannot contain tree structures (elements can)attributes cannot contain tree structures (elements can) attributes are not easily expandable (for future changes)attributes are not easily expandable (for future changes)

Attributes are difficult to read and maintain. Use elementsAttributes are difficult to read and maintain. Use elementsfor data. Use attributes for information that is not relevantfor data. Use attributes for information that is not relevantto the data.to the data.

Don't end up like this:Don't end up like this:

XML Attributes for MetadataXML Attributes for Metadata


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XML Attributes for MetadataXML Attributes for Metadata

Sometimes ID references are assigned to elements. TheseSometimes ID references are assigned to elements. TheseIDs can be used to identify XML elements in much the sameIDs can be used to identify XML elements in much the sameway as the id attribute in HTML. This example demonstratesway as the id attribute in HTML. This example demonstrates

this:this:

ToveToveJaniJani

ReminderReminderDon't forget me this weekend!Don't forget me this weekend!

JaniJaniToveToveRe: ReminderRe: ReminderI will notI will not

The id attributes above are for identifying the differentThe id attributes above are for identifying the differentnotes. It is not a part of the note itself.notes. It is not a part of the note itself.

What I'm trying to say here is that metadata (data aboutWhat I'm trying to say here is that metadata (data about


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XMLXML ValidationValidation

XML with correct syntax is "Well Formed" XML.XML with correct syntax is "Well Formed" XML. XML validated against a DTD is "Valid" XML.XML validated against a DTD is "Valid" XML. Well Formed XML DocumentsWell Formed XML Documents

A "Well Formed" XML document has correct XML syntax.A "Well Formed" XML document has correct XML syntax.The syntax rules were described in the previousThe syntax rules were described in the previous

chapters:chapters: XML documents must have a root elementXML documents must have a root element XML elements must have a closing tagXML elements must have a closing tag

XML tags are case sensitiveXML tags are case sensitive XML elements must be properly nestedXML elements must be properly nested XML attribute values must be quotedXML attribute values must be quoted


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Valid XML DocumentsValid XML Documents

A "Valid" XML document is a "Well Formed" XML document,A "Valid" XML document is a "Well Formed" XML document,which also conforms to the rules of a Document Typewhich also conforms to the rules of a Document TypeDefinition (DTD):Definition (DTD):

ToveToveJaniJaniReminderReminder

Don't forget me this weekend!Don't forget me this weekend!

The DOCTYPE declaration in the example above, is aThe DOCTYPE declaration in the example above, is areference to an external DTD file. The content of the file isreference to an external DTD file. The content of the file isshown in the paragraph below.shown in the paragraph below.


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XML DTDXML DTD

The purpose of a DTD is to define the structure ofThe purpose of a DTD is to define the structure ofan XML document. It defines the structure with aan XML document. It defines the structure with alist of legal elements:list of legal elements:

]>]>


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Why Use a DTD?Why Use a DTD?

With a DTD, each of your XML files can carry aWith a DTD, each of your XML files can carry adescription of its own format.description of its own format.

With a DTD, independent groups of people canWith a DTD, independent groups of people canagree to use a standard DTD for interchangingagree to use a standard DTD for interchanging

data.data.Your application can use a standard DTD to verifyYour application can use a standard DTD to verify

that the data you receive from the outside world isthat the data you receive from the outside world isvalid.valid.

You can also use a DTD to verify your own data.You can also use a DTD to verify your own data.

Th B ildi Bl k f XMLTh B ildi Bl k f XML


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The Building Blocks of XMLThe Building Blocks of XMLDocumentsDocuments

The main building blocks of both XML and HTMLThe main building blocks of both XML and HTMLdocuments are elements.documents are elements.

Seen from a DTD point of view, all XML documentsSeen from a DTD point of view, all XML documents(and HTML documents) are made up by the(and HTML documents) are made up by the

following building blocks:following building blocks: ElementsElements AttributesAttributes EntitiesEntities

PCDATAPCDATA CDATACDATA


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PCDATAPCDATA

PCDATA means parsed character data.PCDATA means parsed character data.Think of character data as the text found betweenThink of character data as the text found between

the start tag and the end tag of an XML element.the start tag and the end tag of an XML element. PCDATA is text that WILL be parsed by aPCDATA is text that WILL be parsed by a

parserparser.. The text will be examined by theThe text will be examined by theparser for entities and markupparser for entities and markup..

Tags inside the text will be treated as markup andTags inside the text will be treated as markup andentities will be expanded.entities will be expanded.

However, parsed character data should notHowever, parsed character data should notcontain any &, characters; these need tocontain any &, characters; these need tobe represented by the & < and >be represented by the & < and >entities, respectively.entities, respectively.


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CDATACDATA

CDATA means character data.CDATA means character data. CDATA is text that will NOT be parsed by aCDATA is text that will NOT be parsed by a

parserparser. Tags inside the text will NOT be treated as. Tags inside the text will NOT be treated asmarkup and entities will not be expanded.markup and entities will not be expanded.

DTD -DTD - ElementsElements


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In a DTD, elements are declared with an ELEMENTIn a DTD, elements are declared with an ELEMENTdeclaration.declaration.

Declaring ElementsDeclaring Elements In a DTD, XML elements are declared with an elementIn a DTD, XML elements are declared with an element

declaration with the following syntax:declaration with the following syntax:

oror

Empty ElementsEmpty Elements Empty elements are declared with the category keywordEmpty elements are declared with the category keyword

EMPTY:EMPTY:

Example:Example:

Elements with Parsed Character DataElements with Parsed Character Data


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Elements with only parsed character data are declared withElements with only parsed character data are declared with#PCDATA inside parentheses:#PCDATA inside parentheses:

Example:Example:

Elements with any ContentsElements with any Contents Elements declared with the category keyword ANY, can containElements declared with the category keyword ANY, can contain

any combination of parsable dataany combination of parsable data

Example:Example:

Elements with Children (sequences)Elements with Children (sequences)


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Elements with one or more children are declared withElements with one or more children are declared withthe name of the children elements inside parentheses:the name of the children elements inside parentheses:

oror

Example:Example:

When children are declared in a sequenceWhen children are declared in a sequenceseparated by commas, the children must appear inseparated by commas, the children must appear inthe same sequence in the document. In a fullthe same sequence in the document. In a fulldeclaration, the children must also be declared,declaration, the children must also be declared,and the children can also have children. The fulland the children can also have children. The full

declaration of the "note" element is:declaration of the "note" element is:


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Declaring Only One Occurrence of an ElementDeclaring Only One Occurrence of an Element

Example:Example:

Declaring Minimum One Occurrence of an ElementDeclaring Minimum One Occurrence of an Element

Example:Example:

The + sign in the example above declares that the child elementThe + sign in the example above declares that the child element"message" must occur one or more times inside the "note""message" must occur one or more times inside the "note"element.element.

Declaring Zero or More Occurrences of an ElementDeclaring Zero or More Occurrences of an Element


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Example:Example:

The * sign in the example above declares that theThe * sign in the example above declares that thechild element "message" can occur zero or morechild element "message" can occur zero or moretimes inside the "note" element.times inside the "note" element.

Declaring Zero or One Occurrences of an ElementDeclaring Zero or One Occurrences of an Element


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Example:Example:

The ? sign in the example above declares that theThe ? sign in the example above declares that thechild element "message" can occur zero or onechild element "message" can occur zero or onetime inside the "note" element.time inside the "note" element.

Declaring either/or ContentDeclaring either/or Content


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Example:Example:

The example above declares that the "note"The example above declares that the "note"element must contain a "to" element, a "from"element must contain a "to" element, a "from"element, a "header" element, and either aelement, a "header" element, and either a

"message" or a "body" element."message" or a "body" element.

Declaring Mixed ContentDeclaring Mixed Content

Example:Example:

message)*>

The example above declares that the "note"The example above declares that the "note"

element can contain zero or more occurrences ofelement can contain zero or more occurrences of" " " " " "" " " " " "

DTD -DTD - AttributesAttributes


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In a DTD, attributes are declared with an ATTLISTIn a DTD, attributes are declared with an ATTLISTdeclaration.declaration.

Declaring AttributesDeclaring Attributes An attribute declaration has the following syntaxAn attribute declaration has the following syntax

attribute-type default-value>attribute-type default-value>

DTD example:DTD example:

XML example:XML example:

TheThe attribute-typeattribute-type can be one of the following:can be one of the following:


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A Default Attribute ValueA Default Attribute Value


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DTD:DTD:

Valid XML:Valid XML:

In the example above, the "square" element isIn the example above, the "square" element is

defined to be an empty element with a "width"defined to be an empty element with a "width"attribute of type CDATA. If no width is specified, itattribute of type CDATA. If no width is specified, ithas a default value of 0.has a default value of 0.

#REQUIRED#REQUIREDSyntaxSyntax

attribute-type #REQUIRED>attribute-type #REQUIRED>

ExampleExample


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DTD:DTD:


Invalid XML:Invalid XML:

Use the #REQUIRED keyword if you don't have anUse the #REQUIRED keyword if you don't have an

option for a default value, but still want to forceoption for a default value, but still want to forcethe attribute to be present.the attribute to be present.

#IMPLIED#IMPLIED


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SyntaxSyntax

#IMPLIED>

ExampleExample

DTD:DTD:



Use the #IMPLIED keyword if you don't want to force theUse the #IMPLIED keyword if you don't want to force the

author to include an attribute, and you don't have an optionauthor to include an attribute, and you don't have an option

#FIXED#FIXED

SyntaxSyntax


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SyntaxSyntax

#FIXED "value">

ExampleExample

DTD:DTD:


Invalid XML:Invalid XML:

Use the #FIXED keyword when you want an attribute toUse the #FIXED keyword when you want an attribute tohave a fixed value without allowing the author to change it.have a fixed value without allowing the author to change it.

If an author includes another value, the XML parser willIf an author includes another value, the XML parser will

Enumerated Attribute ValuesEnumerated Attribute Values


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SyntaxSyntax

en2|..) default-value>en2|..) default-value>

ExampleExample

DTD:DTD:

XML example:XML example:oror

Use enumerated attribute values when you wantUse enumerated attribute values when you wantthe attribute value to be one of a fixed set of legalthe attribute value to be one of a fixed set of legal

values.values.

Some Examples Some Examples TV Schedule DTDTV Schedule DTD


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TV Schedule DTDTV Schedule DTD

]>]>

Newspaper Article DTDNewspaper Article DTD


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(HEADLINE,BYLINE,LEAD,BODY,NOTES)>

]>]>

Product Catalog DTDProduct Catalog DTD


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(SPECIFICATIONS+,OPTIONS?,PRICE+,NOTES?)>INVENTORY (InStock|Backordered|Discontinued) "InStock">

POWER CDATA #IMPLIED>

CASE (HardShell|Soft|NotApplicable) "HardShell">

SHIPPING CDATA #IMPLIED>

]>]>

DTD SummaryDTD Summary


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This tutorial has taught you how to describe theThis tutorial has taught you how to describe thestructure of an XML document.structure of an XML document.

You have learned how to use a DTD to define the legalYou have learned how to use a DTD to define the legalelements of an XML document, and how a DTD can beelements of an XML document, and how a DTD can bedeclared inside your XML document, or as an externaldeclared inside your XML document, or as an externalreference.reference.

You have learned how to declare the legal elements,You have learned how to declare the legal elements,

attributes, entities, and CDATA sections for XMLattributes, entities, and CDATA sections for XMLdocuments.documents.You have also seen how to validate an XML documentYou have also seen how to validate an XML document

against a DTD.against a DTD.


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XML SchemaXML Schema

W3C supports an XML-based alternative to DTD, called XMLW3C supports an XML-based alternative to DTD, called XMLSchema:Schema:


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XMLXML ValidatorValidator

Use our XML validator to syntax-check your XML.Use our XML validator to syntax-check your XML.

XML Errors Will Stop YouXML Errors Will Stop You Errors in XML documents will stop your XMLErrors in XML documents will stop your XML

applications.applications.The W3C XML specification states that a programThe W3C XML specification states that a program

should stop processing an XML document if it findsshould stop processing an XML document if it findsan error. The reason is that XML software shouldan error. The reason is that XML software shouldbe small, fast, and compatible.be small, fast, and compatible.

HTML browsers will display documents with errorsHTML browsers will display documents with errors(like missing end tags). HTML browsers are big and(like missing end tags). HTML browsers are big andincompatible because they have a lot ofincompatible because they have a lot ofunnecessary code to deal with (and display) HTMLunnecessary code to deal with (and display) HTML

errors.errors.


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Syntax-Check Your XMLSyntax-Check Your XML

To help you syntax-check your XML, we haveTo help you syntax-check your XML, we havecreated an XML validator.created an XML validator.

Paste your XML into the text area below, andPaste your XML into the text area below, and

syntax-check it by clicking the "Validate" button.syntax-check it by clicking the "Validate" button.


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h k il


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Syntax-Check an XML FileSyntax-Check an XML File

You can syntax-check an XML file by typing theYou can syntax-check an XML file by typing theURL of the file into the input field below, and thenURL of the file into the input field below, and thenclick the "Validate" button:click the "Validate" button:

Validate Your XML Against aValidate Your XML Against a


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Validate Your XML Against aValidate Your XML Against aDTDDTD

If you know DTD, and you run Internet Explorer, you can validate your XML inIf you know DTD, and you run Internet Explorer, you can validate your XML inthe text area below.the text area below. Just add the DOCTYPE declaration to your XML and click the "Validate"Just add the DOCTYPE declaration to your XML and click the "Validate"

button:button:

]>]>ToveToveJaniJaniReminderReminderDon't forget me this weekend!Don't forget me this weekend!

Vi i

XML Fil


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ViewingViewing XML FilesXML Files

Raw XML files can be viewed in all major browsers.Raw XML files can be viewed in all major browsers. Don't expect XML files to be displayed as HTMLDon't expect XML files to be displayed as HTML

pages.pages.

Viewing XML FilesViewing XML Files


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The XML document will be displayed with color-The XML document will be displayed with color-coded root and child elements. A plus (+) or minuscoded root and child elements. A plus (+) or minussign (-) to the left of the elements can be clicked tosign (-) to the left of the elements can be clicked toexpand or collapse the element structure. To viewexpand or collapse the element structure. To view

the raw XML source (without the + and - signs),the raw XML source (without the + and - signs),select "View Page Source" or "View Source" fromselect "View Page Source" or "View Source" fromthe browser menu.the browser menu.

Note:Note: In Safari, only the element text will beIn Safari, only the element text will be

displayed. To view the raw XML, you must rightdisplayed. To view the raw XML, you must rightclick the page and select "View Source"click the page and select "View Source"

i i lid ilVi i I lid XML Fil


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Viewing an Invalid XML FileViewing an Invalid XML File

If an erroneous XML file is opened, the browser willIf an erroneous XML file is opened, the browser willreport the error.report the error.

O h XML E lOth XML E l


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Other XML ExamplesOther XML Examples

Viewing some XML documents will help you get theViewing some XML documents will help you get theXML feeling.XML feeling.

An XML CD CatalogAn XML CD Catalog


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Why Does XML Display LikeWhy Does XML Display Like


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Why Does XML Display LikeWhy Does XML Display LikeThis?This?

XML documents do not carry information aboutXML documents do not carry information abouthow to display the data.how to display the data.

Since XML tags are "invented" by the author of theSince XML tags are "invented" by the author of theXML document, browsers do not know if a tag likeXML document, browsers do not know if a tag like

describes an HTML table or a dining table. describes an HTML table or a dining table. Without any information about how to display theWithout any information about how to display the

data, most browsers will just display the XMLdata, most browsers will just display the XMLdocument as it is.document as it is.

In the next chapters, we will take a look atIn the next chapters, we will take a look atdifferent solutions to the display problem, usingdifferent solutions to the display problem, usingCSS, XSLT and JavaScript.CSS, XSLT and JavaScript.

Di l iDi l i XML ith CSSXML ith CSS


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DisplayingDisplaying XML with CSSXML with CSS

With CSS (Cascading Style Sheets) you can addWith CSS (Cascading Style Sheets) you can adddisplay information to an XML document.display information to an XML document.

Displaying your XML Files with CSS?Displaying your XML Files with CSS? It is possible to use CSS to format an XMLIt is possible to use CSS to format an XML

document.document. Below is an example of how to use a CSS styleBelow is an example of how to use a CSS style

sheet to format an XML document:sheet to format an XML document:


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XML FILEXML FILE


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XML FILEXML FILE

CSS FILECSS FILE


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CSS FILECSS FILE

Finally, view:Finally, view:


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Finally, view:y,

The CD catalog formatted witThe CD catalog formatted wit

Below is a fraction of the XML file. The second line links the XML file to theBelow is a fraction of the XML file. The second line links the XML file to theCSS file:CSS file:
http://www.w3schools.com/xml/cd_catalog_with_css.xmlhttp://www.w3schools.com/xml/cd_catalog_with_css.xmlhttp://www.w3schools.com/xml/cd_catalog_with_css.xml


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Empire BurlesqueEmpire BurlesqueBob DylanBob DylanUSAUSAColumbiaColumbia10.9010.9019851985

Hide your heartHide your heartBonnie TylerBonnie TylerUKUKCBS RecordsCBS Records9.909.9019881988

..

....

Formatting XML with CSS is not the most common method.Formatting XML with CSS is not the most common method.

Di l i XMLDisplaying XML ith XSLTwith XSLT


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Displaying XMLDisplaying XML with XSLTwith XSLT

With XSLT you can transform an XML documentWith XSLT you can transform an XML documentinto HTMLinto HTML

Displaying XML with XSLTDisplaying XML with XSLT

XSLT is the recommended style sheet language ofXSLT is the recommended style sheet language ofXML.XML.

XSLT (eXtensible Stylesheet LanguageXSLT (eXtensible Stylesheet LanguageTransformations) is far more sophisticated thanTransformations) is far more sophisticated than

CSS.CSS. XSLT can be used to transform XML into HTML,XSLT can be used to transform XML into HTML,

before it is displayed by a browser:before it is displayed by a browser:

XML Code:XML Code:


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Belgian WafflesBelgian Waffles$5.95$5.95two of our famous Belgian Waffles withtwo of our famous Belgian Waffles with

plenty of real maple syrupplenty of real maple syrup

650650

Strawberry Belgian WafflesStrawberry Belgian Waffles$7.95$7.95

light Belgian waffles covered withlight Belgian waffles covered withstrawberries and whipped creamstrawberries and whipped cream900900

B B B l i W ffl /B B B l i W ffl /


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Berry-Berry Belgian WafflesBerry-Berry Belgian Waffles$8.95$8.95light Belgian waffles covered with an assortment of freshlight Belgian waffles covered with an assortment of fresh

berries and whipped creamberries and whipped cream

900900

French ToastFrench Toast$4.50$4.50thick slices made from our homemade sourdoughthick slices made from our homemade sourdough

breadbread

600600

Homestyle BreakfastHomestyle Breakfast$6.95$6.95two eggs, bacon or sausage, toast, and our ever-populartwo eggs, bacon or sausage, toast, and our ever-popular

hash brownshash browns950950

XSLT CodeXSLT Code


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- -

(calories per serving) (calories per serving)


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Transforming XML with XSLT on the ServerTransforming XML with XSLT on the Server In the example above, the XSLT transformation is doneIn the example above, the XSLT transformation is done

by the browser, when the browser reads the XML file.by the browser, when the browser reads the XML file. Different browsers may produce different result whenDifferent browsers may produce different result when

transforming XML with XSLT. To reduce this problem thetransforming XML with XSLT. To reduce this problem theXSLT transformation can be done on the server.XSLT transformation can be done on the server.