Www.monash.edu.au CSE3201 Information Retrieval Systems DTD Document Type Definition

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CSE3201 Information Retrieval Systems

DTD

Document Type Definition

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Valid XML Document

• A well-formed document complies to the syntax specified by W3C recommendation.

• A valid XML document is a well-formed XML document that also complies to the rules specified in a DTD or XML Schema.

• The rules include:– Naming of elements, attributes.– Structure of the document

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DTD Example

<bookshop><book> <title> Harry Potter and the

Philosopher’s Stone</title> <author> <initials>

J.K</initials>

<surname> Rowlings

</surname> </author> <price value=“16.95”>

</price></book>…</bookshop>

<!DOCTYPE bookshop [<!ELEMENT bookshop (book)+><!ELEMENT book (title, author, price)+><!ELEMENT title (#PCDATA)><!ELEMENT author (initials, surname)>

<!ELEMENT initials (#PCDATA)>

<!ELEMENT surname (#PCDATA)><!ELEMENT price EMPTY><!ATTLIST pricevalue CDATA #IMPLIED

>]>

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DOCTYPE declaration

• It is used to declare the name of a document. • The name should be the same to the root element’s

name.

<!DOCTYPE bookshop [ … ]>

NOTE: a DOCTYPE declaration DOES NOT replace a declaration of a root element. The root element needs to be declared separately using an element declaration.

<!DOCTYPE bookshop [<!ELEMENT bookshop (book)+>

… ]>

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ELEMENT declaration

<!ELEMENT elementName contentModel>

• Content model defines what can be included between the opening tag and the closing tag of an element.

• Content Model: any, empty, text only (simple), element only (complex), mixed.

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Content Model - Any

• An element defined with an ANY content model may contain anything, eg elements, character data, comments, etc

<!ELEMENT elementName ANY>

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Content Model - Empty

• An element defined with an empty content model may not contain any text or child element.

<!ELEMENT elementName EMPTY>

• The existence of an attribute does not affect the structure of a content model.

XML:<img src=‘logo.png’/>

DTD:<!ELEMENT img EMPTY>

<!ATTLIST img src CDATA #REQUIRED>

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Content Model – Text only (Simple)

• An element declared with this content model can only contain textual data (simple string) and entity references.

<!ELEMENT elementName (#PCDATA)>

• Example:XML:

<title> Harry Potter and Philosopher’s stone</title>

DTD:

<!ELEMENT title (#PCDATA)>

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Content Model – Element Only (Complex)

• An element declared with this content model may only contain elements and entity references.

<!ELEMENT elementName(childElementName)+>

• Example:

XML:<bookshop>

<book/></bookshop>

DTD:<!ELEMENT bookshop(book)+>

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Content Model - Mixed

• An element declared with this content model may contain intersperse child elements with text.

• Example

XML:<anElement> text mixed with <childElement> child

text</childElement></anElement>

DTD:<!ELEMENT anElement (#PCDATA|childElement)*><!ELEMENT childElement (#PCDATA)>

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Cardinality

• Defines how many child elements may appear for the declared element.

Operator Description

None One and only one child is allowed

? Zero or one child

* Zero or more child(ren)

+ One or more child(ren)

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Sequence Indicator

• Defined the occurrence of the child elements.• Possible occurences:

– “Followed by”=> AND => “ , “– ”Choice of” => OR => “ | “

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Sequence Indicator – “Followed By”

DTD:

<!ELEMENT personName (title,firstName,middleName,lastName,suffix)>

<!ELEMENT title (#PCDATA)><!ELEMENT firstName (#PCDATA)><!ELEMENT middleName (#PCDATA)><!ELEMENT lastName (#PCDATA)><!ELEMENT suffix (#PCDATA)>

XML:

<personName> <title>Mr<Title/> <firstName>John</FirstName> <middleName> V </MiddleName> <lastName> Smart </LastName> <suffix>Jr</Suffix></personName>

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Sequence Indicator – “Choice of”

DTD:<!ELEMENT personName

((Mr |Ms |Dr ),firstName,middleName,lastName,( Jr |Sr))><!ELEMENT Mr EMPTY ><!ELEMENT Ms EMPTY ><!ELEMENT Dr EMPTY ><!ELEMENT firstName(#PCDATA)><!ELEMENT middleName(#PCDATA)><!ELEMENT lastName(#PCDATA)><!ELEMENT Jr EMPTY ><!ELEMENT Sr EMPTY >

XML

<personName> <Mr/> <firstName>John</firstName> <middleName> V </middleName> <lastName> Smart </lastName> <Jr/></personName>

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Attribute Declaration

<!ATTLIST elementNameattrName1 attrType1 attrDefault defaultValue1…attrNameN attrTypeN attrDefault defaultValueN>

DTD:

<!ELEMENT personName EMPTY><!ATTLIST personName

title CDATA #IMPLIEDfirstName CDATA #REQUIREDsurname CDATA #REQUIRED

>

XML:<personName title=“Dr” firstName=“Jenny” surname=“Genius”>

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Attribute Type (some)

Type Description

CDATA Character Data (Simple String)

Enumerated Values

One of a series

ID A unique identifier for each instance of this element type

IDREF A reference to an element with ID type attribute

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Attribute Defaults

Values Description

#REQUIRED Attribute must appear in every instance of the element.

#IMPLIED Attribute is OPTIONAL.

#FIXED (plus default value)

Attribute is OPTIONAL.

If it does appear, it must match the default value.

If it does not appear, the parser may supply the default value.

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#Required - Example

<?xml version="1.0"?><!DOCTYPE friends [<!ELEMENT friends (person)+><!ELEMENT person (personName,email) ><!ELEMENT personName (firstName,surname) ><!ELEMENT firstName (#PCDATA) ><!ELEMENT surname (#PCDATA) ><!ELEMENT email (#PCDATA) ><!ATTLIST person perID ID #REQUIRED>]><friends>

<person perID="p1"><personName >

<firstName> Jenny </firstName><surname> Genius </surname>

</personName><email>[email protected]</email>

</person></friends>

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#Implied - Example <?xml version="1.0"?>

<!DOCTYPE friends [

<!ELEMENT friends (person)+>

<!ELEMENT person (personName,email) >

<!ELEMENT personName (firstName,surname) >

<!ELEMENT firstName (#PCDATA) >

<!ELEMENT surname (#PCDATA) >

<!ELEMENT email (#PCDATA) >

<!ATTLIST person title CDATA #IMPLIED >

]>

… (next slide)

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#Implied - Example

<friends><person title="Dr">

<personName><firstName> Jenny </firstName><surname> Genius </surname>


</person><person>

<personName ><firstName> John </firstName><surname> Howard </surname>


</person></friends>

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#Fixed-Example

<?xml version="1.0"?>

<!DOCTYPE friends [







<!ATTLIST person title CDATA #FIXED "Dr" >

]>

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#Fixed-Valid Instances

<friends><person title="Dr">

<personName><firstName> Jenny </firstName><surname> Genius </surname>


</person><person>

<personName><firstName> John </firstName><surname> Howard </surname>


</person></friends>

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#Fixed – Invalid Instance

<friends>

<person title=“Ms">

<personName>

<firstName> Jenny </firstName>

<surname> Genius </surname>

</personName>

<email>[email protected]</email>

</person>

</friends>

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Entity

• Storage Unit• Entity is declared in DTD (except

predefined entity) and is referred in DTD/XML document.

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Entity Example

<?xml version="1.0"?>

<!DOCTYPE footNote [

<!ELEMENT footNote (#PCDATA)>

<!ENTITY copy "©2001">

<!ENTITY uni "Monash University">

<!ENTITY disclaimer "No warranty © &uni;">

]>

<footNote>All &uni; websites contain the following disclaimer "&disclaimer;"

</footNote>

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External DTD

• Re-use of DTD.• Easy to maintain

– single update• Public DTD

<!DOCTYPE article PUBLIC “MyPublicDTD/Book” http://www.csse.monash.edu.au/DTDs/maria/book.dtd>

• Local DTD<!DOCTYPE article SYSTEM book.dtd>

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External DTD Example

• DTD file







<!ATTLIST person title CDATA #IMPLIED >

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External DTD Example

• XML file<?xml version="1.0" standalone="no"?><!DOCTYPE friends SYSTEM “friends.dtd"><friends>

<person title="Dr"><personName>

<firstName> Jenny </firstName><surname> Genius </surname>


</person></friends>

NOTE: the value of the xml declaration attribute “standalone” has to be set to “no” when an external DTD is used.

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Mixed DTDs

• Internal and external can be mixed.• The external has to be declared first.

<!DOCTYPE article PUBLIC “MyPublicDTD/Book” http://www.csse.monash.edu.au/DTDs/maria/book.dtd

[ DTD declarations …]>

Conflict management:– the internal DTD subset always take priority– the internal DTD will overide the external declaration.

internal DTD subset

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Limitations of DTD

• Non-XML syntax• DTD is not Extensible• Weak Data Typing• No inheritance

• Possible solution: XML Schema

Documents

Www.monash.edu.au CSE3201 Information Retrieval Systems DTD Document Type Definition