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DOCUMENT TYPEDEFINITION (DTD)Compiled & prepared by: NorzilahMusa

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Question?

Is there any way of making sure thatDATA is STRUCTURED in a particularway?

Yes, there is. It is necessary toensure that the data exchange

(sending/ receiving) conforms to aparticular structure. DocumentType Definition (DTD): define the

allowable structures in an XML

An XML document is not required to have acorresponding DTD.

However, DTDs are often recommended to ensuredocument conformity

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Question?

Q: What happen if I dont want thedata validated?

A: If you dont want your XML datavalidated, dont link it to a DTD.

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Parsers, Well-formed and ValidXML Documents

A validity parser is able to read the DTDand determine whether or not the XMLdocument conforms to it.

If the document conforms to the DTD, itis referred to as valid

If the document fails to conform to the

DTD but is syntactically correct, it is well-formed but not valid. By definition, a valid document is well-

formed.

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DTD : Introduction

Allows you to create rules for theelements within your XML documents.

The rules defined in a DTD are specific to

your own needs. XML document to be well-formed

- Use correct XML syntax,- Conform to its DTD or schema

The DTD is declared at the top of XMLdocument.

Contents of the DTD can be includedwithin XML document or external

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DTD : Introduction (contd)

A DTD consists of a list of syntaxdefinitions for each element in your XMLdocument.

DTD means creating a syntax rules forany XML document that uses the DTD.

Specify which element names can be

included in the document, the attributesthat each element can have, whether ornot these are required or optional, andmore.

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Why?

Each XML files can carry a description ofits own format.

Independent groups of people can agree

to use a standard DTD for interchangingdata.

An application can use a standard DTD

to verify that the data it receive from theoutside world is valid.To verify your own data.

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Example

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DTD : Internal

If the DTD is declared inside the XML file,it should be wrapped in a DOCTYPEdefinition with the following syntax:

!DOCTYPE note defines that the rootelement of this DTD

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Example

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DTD: External

ToveJani

Reminder

Don't forget me

this weekend!

(#PCDATA)>

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DTD : XML Building Blocks

All XML documents (and HTMLdocuments) are made up by thefollowing building blocks:

1) Elements main building blocks ofXML2) Attributes extra informations about

element3) Entities - characters have a specialmeaning in

XML4 PCDATA arsed character data

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DTD : XML Building Blocks(contd)

Entity References Character

< >

& &

" "

'

Predefined XML entities

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PCDATA Parsed Character DataThink of character data as the textfound between the start tag and the

end tag of an XML element. PCDATA is text that WILL be

parsed by a parser. The text willbe examined by the parser for

entities and markup. However, parsed character data

should not contain any &, characters; these need to be

represented by the & < and& t; entities, res ectivel .

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CDATA means character data. CDATA is text that will NOT be

parsed by a parser.Tags inside the text will NOT be

treated as markup and entities willnot be expanded.

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DTD : Elements

Elements are declared with anELEMENT declaration

Syntax:

content)>

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Element content

Specific rule1) ANY

- can contain any combination of parsabledata

- remove all syntax checking, NOTadvisable

2) Specific data or another element

- the data type/element name needs to besurrounded by brackets (i.e. (tutorial) or(#PCDATA)).

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Element content (contd)

Empty Element

Syntax :

Example:

Used for elements that do not contain content.In this case, the header element containsnothing.

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Child Elements :Specify an element that contain anotherelement, by providing the name of theelement it must contain.

Syntax :

Example:

XML tutorial

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Multiple Child Elements (Sequences)- More than one elements, used commato

separated the- This is referred to as a "sequence".- The XML document must contain thetags in the

same order that they're specified inthe sequence.

Syntax :

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Elements with only character dataElements with only character data are

declared with #PCDATA inside

parentheses: Syntax :

Example:

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Example

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Declaring only one occurrence ofthe same element

Syntax

Example:

The example declaration above declaresthat the child element message can only

occur one time inside the "note" element

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Declaring minimum oneoccurrence of the same element.

Syntax:

Example:

The + sign in the example abovedeclares that the child element messagemust occur one or more times inside the"note" element.

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Example : Plus indicator

An elements frequency (i.e., number ofoccurrences) is specified by using either

theplus (+), astrerisk(*) or questionmark(?) occurrence indicator.

The example specifies that element

album contains one or more songelements.

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Declaring zero or more occurrencesof the same element

Example:

The * sign in the example above

declares that the child element messagecan occur zero or more times inside the"note" element.

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Example : Asterik indicator

indicates that element library containsany number ofbook elements, including

the possibility of none at all. Markupexamples that conform to this:

The nationsThe IliadThe Jungle

and

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Declaring zero or one occurrences ofthe same element

Syntax :

name?)> Example:

The ? sign in the example abovedeclares that the child element messagecan occur zero or one times inside the"note" element.

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Example : ? indicator

indicates that element seat contains atmost oneperson element. Examples of

markup that conform to this are:

Maya Karin

and

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Declaring either/or content Example:

body))>The example above declares that the

"note" element must contain a "to"element, a "from" element, a "header"element, and either a "message" or a"body" element

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Example : Pipe character (|)

Eg:

Choices are specified using thepipecharacter (|)

The example specifies that element

dessert must contain either oneicecreamelement or onepastryelement, but not both. The contentspecification may contain any number of

i e character-se arated choices.

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dessert elements contains of either a

single ice-cream element or a singlecoffee element.

A valid example:

vanilla

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Invalid example (well formed but notvalid under this element typedeclaration):

Apple

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Declaring mixed content

Example:

The example above declares that the

"note" element can contain parsedcharacter data and any number of "to","from", "header", and/or "message"elements.

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This notation is used for elements withmixed content, that is, character data andfurther elements. In this case, an order

element can consist of a mixture of atleast zero or more character data andmenu elements in any order.

For example:

The customer will have:

Chicken Soup

Apple Pie

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DTDExample.doc

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An example of markup that conforms to thisis:

XML Classical Hits

XML Overture

10

XML Symphony 1.0

54

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(credit|noCredit))>

Markup examples:123Dr. Ayip4

and456PutehMuhammad3

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Markup example:

grapehalf-sour

sourhalf-sourchocolate

and

semi-sweetwhippedsweet

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Summary

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Summary

Description of Element Type Model:

EMPTY (specifying an element with no content) ANY (specifying an element that can contain any

elements and character data)

#PCDATA (specifying a single element that contains

character data) , (specifying an element to contain sub-elements: exactly

one occurrence allowed)

| (specifying a list of sub-elements: Only one occurrence

allowed) ? (specifying a sub-element that occurs onceor not at

all)

+ (specifying sub-elements that occur at least once and

possibly more)

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K-Break

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Element Structure

Create Element or Attribute?- Particular part of document -> Element- Provide detail to an existing bit of data

-> Attribute

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Norzilah Musa/Jul2010/CSC570

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DTD - Attributes

In a DTD, Attributes are declared with anATTLIST declaration.

Declaring Attributes

An attribute declaration has the followingsyntax:

DTD example:

XML example:

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Attribute list declarations

Attributes:- further describe a noun- anelement.

Attribute list declarations generally

describe four key aspects:1) The element to which the attribute isassociated2) The name of the attribute

3) The type of the attribute4) What the parser should do in case anattribute value is not supplied (that is, thedefault value)

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Quotes- Place quotation marks around theattribute's value

Example:

XML

Attributes : Example


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Attributes : Example

AnnaSmith

female

AnnaSmith


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Attribute TypeThe attribute-type can have the following

values:

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Attribute Type : CDATA

Character data, numbers, text that is notparsed.

Example

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Attribute Type : CDATA

Strings in attribute types are like stringsin all programming a series ofcharacter data. In XML, string lengthsnot defined.

The CDATA keyword implies a string.Strings can contain all text charactersexcept for special characters like

quotation marks and ampersands(symbols). BawangMerah Bawang Putih


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Attribute Type : NMTOKEN

Text with some restriction Numbers, letters, !xml Symbols : _ , - , . , : ! Space

Attribute Type : (value 1 |

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Attribute Type : (value-1 |value -2)

A value list a set of acceptable optionsfor the attribute to contain

Example

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Attribute Type : ID

A unique id, identifies particular element Work together with IDREF cross

referencing of elements

Example

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Attribute Type : IDREF

A unique id reference value that pointsto another elements ID value

Example

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Attribute Type : ENTITY

Attribute value is an entity An entity is a value that has been

defined elsewhere in the DTD to have

particular meaning. Example

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Attribute Type : NOTATION

Attribute value is a notation A notation is a description of how

information should be processed.

To define a helper application or plug-in ,image datatype require specific viewer,state the location, parameter

Example

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Attribute Default : Default

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Attribute Default : Defaultvalue

DTD:

Valid XML:

In the example above, the "square"

element is defined to be an emptyelement with a "width" attribute of typeCDATA. If no width is specified, it has adefault value of 0.

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Attribute Default :

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Attribute Default :#IMPLIED

Syntax

- Optional; may be ignored if no value

Example

DTD:

Valid XML:

Valid XML:

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Attribute Default :

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Attribute Default :#FIXED

Syntax

type #FIXED "value">

Example

DTD:

Valid XML:

Invalid XML:

Use the #FIXED keyword when you want anattribute to have a fixed value withoutallowing the author to change it. If an authorincludes another value, the XML parser will

return an error.

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E i

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Exercise

DTD Exercise.doc

DTD E i i

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DTD - Entities

Entity The value is entityEntities The value is a list of

entityEntities are variables used to

define shortcuts to common text.

Entity references are referencesto entities.

Entities can be declared internal,

or external

DTD Entities (contd)

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DTD Entities (cont d)

The ENTITY/ ENTITIES keyword is used inthe declaration to tell the parser to goand find the unparsed entity and pop it

into the value of the attribute.

Has three parts:1) ampersand (&)2) entity name3) semicolon (;)


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Internal Entity

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Internal EntityDeclaration

Syntax:

DTD Example:

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Exercise

CSC570 -> April 2008, Question 1, PartB.

70Norzilah Musa/Jul2010/CSC570

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DTD - EXAMPLESFROM THE NET

TV S h d l DTD

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TV Schedule DTDBy David Moisan. Copied from his Web: http://www.davidmoisan.org/71

http://www.davidmoisan.org/http://www.davidmoisan.org/

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DTD Li it ti

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DTD Limitations

Non-XML syntax

DTD is not Extensible

Weak Data Typing

No inheritance

Possible solution: XML Schema

B i T

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Brain Teaser

How could all ofyour cousins havean aunt who is

not your aunt?

B i T

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Brain Teaser