AdvXML Lecture02 DTD

8/12/2019 AdvXML Lecture02 DTD

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Explain DTD Create DTD:

Declaring ElementsDeclaring Attributes

Declaring Entities

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A feature of SGML, inherited by XML. Contains the list of tags that specifies the

grammatical structure of an XML document.

DTD defines the way elements relate to one anotherwithin the documents tree structure, and specifiesthe attributes.

DTD are of two types: An external DTD An internal DTD

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Provide an application independent way of sharingdata.

Interchangedata between independent groups ofpeople.

Can be used by the application to verifythat valid datahas been entered.

Defines the legal building blocks of an XMLdocument.

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type) >

name attribute-nameattribute-type

default-value>

]>

DOCTYPE declaration

ELEMENT declaration

ATTRIBUTE

declaration

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Written directly in theXML document after the

XML declaration.

Writing the DTD withinthe DOCTYPE definitionis called as Wrapping.

The file with the DTDand XML code has a .xmlextension.

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The DTD reference in the XML document file:

The show.dtd file:

Exists outside thecontent of a

document.

The DTD file hasa .dtdextension.

Reference to theDTD file is added at

the beginning of theXML file.

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XML elements are declared with an element declaration. Syntax

Example

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EMPTY element content type specifies that theelement has no child elements or character data.

Syntax

Example

Empty elements with attributes are possible:

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Syntax

or

Where:#PCDATA = element contains character data that is to be parsed

ANY = element with any content

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Elements with one or more children are defined with the nameof the child element inside the parentheses.

Syntax

Example

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Element occurrences

Only one occurrence

Minimum one

occurrence

element-name

(child-name+)>

Zero or more

occurrences

element-name

(child-

name*)>

Zero or one occurrence

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Elements can have attributes. Syntax

Example

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Value Explanation

CDATA The value is character data

(eval|eval|..) The value must be an enumerated value

ID The value is an unique id

IDREF The value is the id of another element

IDREFS The value is a list of other ids

NMTOKEN The value is a valid XML name

NMTOKENS The value is a list of valid XML names

ENTITY The value is an entity

ENTITIES The value is a list of entities

NOTATION The value is a name of a notation

xml: The value is predefined

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Value Explanation

#DEFAULT The attribute has a default value.

#REQUIREDThe attribute value must be included in the

element.

#IMPLIED The attribute does not have to be included.

#FIXED The attribute value is fixed.

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Entities that have their contents within the XMLdocument are called internal entities.

Syntax

Example


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Entities whose contents are found outside theXML document are called external entities.

They are declared using the SYSTEM keyword. Syntax

Example

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A well-formed document is one that conforms to the basicrules of XML.

A valid document is well formed and is also validated againsta DTD.

The DTD specifies the grammatical structure of an XMLdocument, by allowing XML parsers to understand andinterpret the documents contents.

The use of the SYSTEM keyword indicates to the parser thatthis is an external declaration, and that the set of rules for this

XML document can be found in a specified file. EMPTY element content type specifies that the element has

no child elements or character data.

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#CDATA means that the element contains character data that is notto be parsed by a parser.

#PCDATA means that the element contains data that is to be parsed

by a parser.

Specifying a default value for an attribute in the DTD ensures thatthe attribute will get a value, even if the author of the XML

document does not include it.

Specifying the value of an attribute as Implied means that theparticular attribute is not mandatory and can be specified in theXML document.

Specifying the value of an attribute as Required means that theparticular attribute is mandatory (that is, its value must be provided

in the XML document).

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ID is the identifier type, and should be unique. Thisattribute value is used to search for a particular instance ofan element. Each element can only have one attribute of typeID.

A DTD can be either External or Internal.

Entities allow us to create an alias to some large piece oftext, so that, in the document, the same piece of text can bereferred to, simply by referring to the alias.

Namespaces allow us to combine documents from differentsources, and be able to identify which elements or attributescome from which source.

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Documents

AdvXML Lecture02 DTD