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New Perspectives on XML, 2nd EditionTutorial 2

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TUTORIAL 2

WORKING WITH NAMESPACES

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COMBINING XML VOCABULARIES

• A document that combines several vocabularies is known as a compound document

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WORKING WITH NAMESPACES

• Name collision occurs when elements from two or more documents share the same name.

• Name collision is not a problem if you are not concerned with validation. The document content only needs to be well-formed.

• However, name collision will keep a document from being validated.

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NAME COLLISION

This figure shows name collision

Partsvocabulary

Modelvocabulary

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DECLARING A NAMESPACE

• A namespace is a defined collection of element and attribute names.

• Names that belong to the same namespace must be unique. Elements can share the same name if they reside in different namespaces.

• Namespaces must be declared before they can be used.

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• A namespace can be declared in the prolog or as an element attribute. The syntax for an attribute used to declare a namespace in the prolog is:

xmlns:prefix=“URI”

where URI is a Uniform Resource Identifier that assigns a unique name to the namespace

prefix is a string of letters

“Short hand name” Full, unique name

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• For example,

xmlns:mod=“http://jacksonelect.com/models”

declares a namespace with the prefix “mod” and the URI

http://jacksonelect.com/models

• The URI is not a Web address. A URI (Uniform Resource Identifier) identifies a physical or an abstract resource.

URI (Uniform Resource Identifier)

URL (Uniform Resource Locator)Physical Resource: file, a Web page, or

an e-mail address

URN (Uniform Resource Name)Persistent name for a resource

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URIs, URLs, AND URNs

• URN (Universal Resource Name) is a persistent resource identifier, meaning the user need only know the name of a resource.

• URNs take the form: urn:NID:NSSNID = namespace identifierNSS = text string specific to that the namespace

• Example– urn: isbn: 0-619-01969-7

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APPLYING A NAMESPACE TO AN ELEMENT

• Use prefix instead of the URI to qualify element names• General form:

<prefix:element> content</prefix:element>

• For example

xmlns:mod=http://jacsonelect.com/models

<mod:title>Laser4C (PR205) </mod:title>

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APPLYING A NAMESPACE TO AN ELEMENT

• Prefixed names are called qualified names• Example:

<mod:title>Laser4C (PR205) </mod:title>

• A name without a namespace prefix is called an unqualified name.

• Example: <title>Laser4C (PR205) </title>

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DECLARING A NAMESPACE AS AN ELEMENT ATTRIBUTE

• For example, the code:<mod:model xmlns:mod=http://jacksonelect.com/modes >

<mod:title>Laser4C (PR205)</mod:title><mod:description>Entry level color laser printer</mod:description><mod:type>color laser</mod:type><mod:ordered>320</mod:ordered><mod:parts list="chx201,fa100-5,eng005-2,cbx-450V4,tn01-53" />

</mod:model>

• …applies the namespace http://jacksonelect.com/models

to the model element and all of its child elements.

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DECLARING A DEFAULT NAMESPACE

• You can specify a default namespace by omitting the prefix in the namespace declaration.

• Example:<model xmlns=http://jacksonelect.com/modes >

<title>Laser4C (PR205)</title><description>Entry level color laser printer</description><type>color laser<type><ordered>320</ordered><parts list="chx201,fa100-5,eng005-2,cbx-450V4,tn01-53" />

</model>• All elements including the model element, are considered

to be part of the name space

:mod removed

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USING NAMESPACES WITH ATTRIBUTES

• Attributes, like elements, can become qualified by adding the namespace prefix to the attribute name. The syntax is:

<element prefix:attribute = “value”> … </element>• For example:

<mod:model xmlns:mod=http://jacksonelect.com/models

mod:id=“pr205”>

….

</mod:model>

• Attributes inherit their namespace from their parent element:

• For example:

<mod:model xmlns:mod=http://jacksonelect.com/models

id=“pr205”>

…..

</mod:model>

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ADDING A NAMESPACE TO A STYLE SHEET:


• To declare a namespace in a style sheet, you add the following rule to the style sheet file

@namespace prefix url(uri);

Where prefix is the namespace previx and uri is the URI of the namespace

• Example:

@namespace mod url(http://jacksonelect.com/models)

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APPLYING A NAMESPACE TO A SELECTOR

• Once you’ve declared a namespace in a style sheet, you can associate selectors with that namespace using the syntax:

prefix|selector {attribute1:value1; attribute2:value2;…}

• For example:

mod|title {width: 150px}

• You also can use the wildcard symbol (*) to apply a style to any element within a namespace or to elements across different namespaces

XPAPPLYING A NAMESPACE TO A SELECTOR

• You also can use the wildcard symbol (*) to apply a style to any element within a namespace or to elements across different namespaces

mod | title {width: 15px}

applies width style to all title elements in the models namespace

mod | * {font-size: 12 pt}applies the font-sie style to any element within the models namespace

title {witdth: 15p}

applies a width of 150 pixels to any element named title

• Not supported by Firefox, Opera, and Netscape


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COMBINING STANDARD VOCABULARIES

• Standard vocabularies may be combined within single documents

XPA compound XHTML and MathML document

• See page XML 68


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XHTML

XPSummary

• Combining vocabularies in a single document can result in name collisions

• Use namespaces to resolve collisions• Namespaces use URI to provide unique identification

for each vocabulary in a document• CSS style sheets can be modified to accommodate

namespaces• You can create an XHTML document that combines

features from XHTML and other XML vocabularies


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