03 - XML - DTD

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eXtensible Markup LanguageLectu rer : Phan Vo Minh Than g MSc.

eXtensible Markup Language

Document Type Definitions (DTDs)

eXtensible Markup Language Phan Vo Minh Thang

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XML Lectures Notes Document Type Definition

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< e s o 0 > < ate a > ectu es otes ocu e t ype e t o

Element Declaration

DTD is a mechanism to describe every object (element,attribute,) that can appear in an XML document

Element Declaration

Content specification specifies what children the element may or musthave in what order

Parentheses are used to group elements in content specification

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yp

Special Keywords in Content Model

Special Keywords in Content Model #PCDATA: parsed character data (text)

CDATA sections appear anywhere #PCDATA appears

EMPTY: empty element

ANY: can contain any other elements declared in the DTD

(including mixed content, child elements)

Mixed Content

Element contents that have #PCDATA Element Content

Element contents that contain only elements

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yp

The Secret of +, *, ?

+, *, ?: Occurrence indicators No occurrence indicator: appear once and only once

+: appear one or several times

*: appear zero or more times

?: appear once or not at all

Example

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The Secret of , |

, | : Connectors , : Elements must appear in the same order

| : Only one element must appear

Examples

Mixed Content: Components must always separated by a |,and the model must repeat

PCDATA must be the first child in the list

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More Examples

footnote | emphasize | date)* >

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Attribute Declaration

Attribute Declaration

value>

preferred (true|false) false>

Can appear anywhere in the DTDBest to list attributes immediately after the element declaration

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Attribute Type

CDATA: String

ID: Identifier unique in the document

IDREF: Value of an ID

IDREFS: List of IDREF separated by space

ENTITY: Name of an external entity

ENTITIES: List of ENTITY

NMTOKEN: Word without spaces

NMTOKENS: List of NMTOKEN

Enumerated-type list: Closed list of NMTOKEN separatedby |

Notation: name of a notation declared in the DTD

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Attribute Types (Cont.)

CDATA Any text string acceptable in a well-formed XML attribute value

The most general attribute type

Can be used for prices, URIs, email addresses, citations

NMTOKEN (named token)

Consist of the same characters as an XML name, but any allowed

characters can be the first character in a name token

12, .cshrc

NMTOKENS

one ore more XML name tokens separated by whitespace

Katand the Kings

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Enumeration A list of all possible values for the attribute, separated by |

Each possible value must be an XML name token

ID assign unique identifiers to elements

An XML name that is unique within the XML document (no other IDtype attribute in the document can have the same value)

Each element must have no more than one ID type attribute

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IDREF Refer to the ID type attribute of some element in the document

Used to establish relationships between elements when simple

containment won't suffice

Do not constrain the person attribute of the team_member elementto match only employee IDs or constrain the project_id attribute ofthe assignment element to match only project IDs

IDREFS

Contain a whitespace-separated list of XML names, each of which

must be the ID of an element in the document

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ENTITY Contain the name of an unparsed entity declared elsewhere in

DTD

ENTITIES

Contain the name of one ore more unparsed entities declaredelsewhere in the DTD, separated by whitespace

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NOTATION Contain the name of a notation declared in the document's DTD

It could be used to associate types with particular elements, as

well as limiting the types associated with the element

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Default Value

#REQUIRED The attribute is required. Each instance of the element must

provide a value for the attribute

No default value is provided

#IMPLIED

The attribute is optional. Each instance of the element may or maynot provide a value for the attribute

No default value is provided

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Default Value (Cont.)

#FIXED (follow by a value) The attribute value is constant and immutable. The attribute has

the specified value regardless of whether the attribute is explicitlynoted on an individual instance of the element

If it is included, it must have the specified value

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Limitation of DTD

Limitations of DTD Content is limited to textual

Difficult to put in repetition constraints

DTD does not use XML syntax

DTD does not say the following

What the root element of the document is

How many of instances of each kind of element appear in thedocument

What the character data inside the elements looks like

The semantic meaning of an element

A DTD never says anything about the length, structure, meaning,allowed values, or other aspects of the text content of an element

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Advanced DTD

General Entity Declaration

External Parsed General Entities

External Unparsed Entities and Notations

Parameter Entities

Conditional Inclusion

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Validation

A validating parser compares a document to its DTD andlists any places where the document differs from theconstraints specified in the DTD

The parser can decide what it wants to do about any violationsA validity error is not necessarily a fatal error

Validation is an optional step in processing XML

Everything not permitted in the DTD is forbidden

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Info

Course name:Special Selected Topic in

Information System Section: Document Type Definitions (DTDs)

Number of slides: 29

Updated date: 12/02/2006 Contact: Mr.Phan Vo Minh Thang

([email protected])

Documents

03 - XML - DTD