New Perspectives on XML, 2nd Edition

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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

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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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DECLARING A NAMESPACE

• 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
• xmlnsprefixURI
• Where URI is a Uniform Resource Identifier that
  assigns a unique name to the namespace, and
  prefix is a string of letters that associates
  each element or attribute in the document with
  the declared namespace.

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DECLARING A NAMESPACE

• For example,
• ltmode1 xmlnsmodhttp//jacksonelect.com/models
  gtgt
• Declares a namespace with the prefix mod and
  the URI http//jacksonelect.com/models
• The URI is not a Web address. A URI identifies a
  physical or an abstract resource.

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URIs, URLs, AND URNs

• A physical resource is a resource one can access
  and work with such as a file, a Web page, or an
  e-mail address. A URL is one type of URI.
• An abstract resource is one that doesnt have any
  physical existence, the URI is used as an
  identifier or an ID.

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URIs, URLs, AND URNs

• A proposed type of URI is the URN or Universal
  Resource Name. A URN is a persistent resource
  identifier, meaning the user need only know the
  name of a resource. An agency would then retrieve
  a copy of the resource independent of its
  location.
• URNs take the form
• urnNIDNSS

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APPLYING A NAMESPACE TO AN ELEMENT

• Once it has been declared and its URI specified,
  the namespace is applied to elements and
  attributes by inserting the namespace prefix
  before each element name that belongs to the
  namespace.
• ltprefixelementgt
• content
• lt/prefixelementgt
• Here, prefix is the namespace prefix and element
  is the local part of the element name.

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APPLYING A NAMESPACE TO AN ELEMENT

• Prefixed names are called qualified names and an
  element name without a namespace prefix is called
  an unqualified name.
• Qualified names can be added to a document using
  code entered directly into the document.
• However, the more common way is to add the xmlns
  attribute to an element.

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DECLARING A NAMESPACE AS AN ELEMENT ATTRIBUTE

• The syntax is
• xmlnsprefixURI
• Where prefix and URI are the prefix and URI for
  the namespace.

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DECLARING A NAMESPACE AS AN ELEMENT ATTRIBUTE

• For example, the code
• ltmodmodel xmlnsmod"http//jacksonelect.com/mode
  ls"gt
• ltmodtitlegtLaser4C (PR205)lt/modtitlegt
• ltmoddescriptiongtEntry level color laser
  printerlt/moddescriptiongt
• ltmodtypegtcolor laserlt/modtypegt
• ltmodorderedgt320lt/modorderedgt
• ltmodparts list"chx201,fa100-5,eng005-2,cbx-450V4
  ,tn01-53" /gt
• lt/modmodelgt

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DECLARING A NAMESPACE AS AN ELEMENT ATTRIBUTE

• applies the namespace http//jacksonelect.com/mod
  els namespace to the model element and all of its
  child elements.
• While the mod prefix was only added to the
  model element name, the XML parser considers the
  other elements parts of the model namespace and
  they inherit the namespace.

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DECLARING A NAMESPACE AS AN ELEMENT ATTRIBUTE

• They are unqualified elements, though, because
  they lack a namespace prefix.
• Declaring a namespace by adding it as an
  attribute of the documents root element places
  all elements in the namespace.
• All elements thus are children of the root
  element.

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DECLARING A DEFAULT NAMESPACE

• You can specify a default namespace by omitting
  the prefix in the namespace declaration.
• The element containing the namespace attribute
  and all of its child elements are assumed to be
  part of the default namespace.

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USING NAMESPACES WITH ATTRIBUTES

• Attributes, like elements, can become qualified
  by adding the namespace prefix to the attribute
  name. For example,
• ltelement xmlnsurigt contentlt/elementgt

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USING NAMESPACES WITH ATTRIBUTES

• No element may contain two attributes with the
  same name.
• No element may contain two qualified attribute
  names with the same local part, pointing to
  identical namespaces, even if the prefixes are
  different.

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ADDING A NAMESPACE TO A STYLE SHEET DECLARING A
NAMESPACE

• To declare a namespace in a style sheet, you add
  the following rule to the style sheet file
• _at_namespace prefix url(uri)
• Where prefix is the namespace previx and uri is
  the URI of the namespace
• Example
• _at_namespace mod url(http//jacksonelect.com/models)

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APPLYING A NAMESPACE TO A SELECTOR

• Once youve declared a namespace in a style
  sheet, you can associate selectors with that
  namespace using the syntax
• prefixselector attribute1value1
  attribute2value2
• For example
• modtitle 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

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DEFINING NAMESPACES WITH THE ESCAPE CHARACTER

• Not all browsers support the use of the
  _at_namespace rule
• A proposal implement in the Internet Explorer
  browser was to insert the backslash escape
  character before the namespace prefix in CSS
  style sheets
• prefix\selector attribute1value1
  attribute2value2
• Browsers like Firefox, Opera, and Netscape do not
  support this method with XML documents

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DECLARING AND APPLYING A NAMESPACE IN A STYLE
SHEET

• To declare a namespace in a CSS style sheet, add
  the following rule before any style declarations
• _at_namespace prefix url(uri)
• where prefix is the namespace prefix and uri is
  the namespace URI. If no prefix is specified, the
  namespace URI is the default namespace for
  selectors in the style sheet.
• To apply a namespace to a selector, use the form
  prefixselector attribute1value1
  attribute2value2 ...
• where prefix is the namespace prefix and
  selector is a selector for an element or group of
  elements in the document.
• For Internet Explorer browsers, use the following
  form to apply a namespace to a selector
• prefix\selector attribute1value1
  attribute2value2 ...

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COMBINING STANDARD VOCABULARIES

• Standard vocabularies may be combined within
  single documents

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CONVERTING HTML TO XHTML

• Use your text editor to open the reptxt.htm file
  from the tutorial.02x/tutorial folder. Enter your
  name and the date in the comment section at the
  top of the document. Save the file as report.htm.
• Insert the following xml declaration as the very
  first line in the file (above the comment
  section)
• lt?xml version"1.0" encoding"UTF-8"
  standalone"yes" ?gt
• Add the following attribute to the opening lthtmlgt
  tag
• xmlns"http//www.w3.org/1999/xhtml"

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CONVERTING HTML TO XHTML
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ADDING THE ELEMENTS OF THE PARTS VOCABULARY

• Return to the order.xml file in your text editor.
• Copy the parts element from the parts namespace,
  including all of the elements and contents it
  contains.
• Return to the report.htm file in your text editor
  and paste the copied elements directly below the
  h2 heading Parts List.
• Add the following attribute to the opening lthtmlgt
  tag
• xmlnspa"http//jacksonelect.com/parts"
• Below the link element that links the report.htm
  file to the report.css style sheet, insert the
  following link element
• ltlink rel"stylesheet" href"parts.css"
  type"text/css" /gt
• Save the changes and open the report.htm file in
  your Web browser

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ADDING THE ELEMENTS OF THE PARTS VOCABULARY
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DESCRIBING THE ITEMS IN THE PARTS LIST

• Return to the report.htm file in your text
  editor.
• Scroll down to the first title element in the
  parts namespace. Directly after the opening
  ltpatitlegt tag, insert the text
• ltspangtTitlelt/spangt
• Directly after the opening ltpadescriptiongt tag
  in the next line, insert the text
• ltspangtDescriptionlt/spangt
• Directly after the opening ltpainstockgt tag in
  the following line, insert the text
• ltspangtParts in Stocklt/spangt
• Repeat the previous 3 steps, as necessary

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DESCRIBING THE ITEMS IN THE PARTS LIST
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DESCRIBING THE ITEMS IN THE PARTS LIST
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ADDING ELEMENTS FROM THE MODELS VOCABULARY

• Return to the report.htm file in your text editor
  and add the following namespace declaration to
  the opening lthtmlgt tag
• xmlnsmod"http//jacksonelect.com/models"
• Add the following link to the documents head
• ltlink rel"stylesheet" href"model.css"
  type"text/css" /gt
• In the table cell directly after the Title table
  heading, insert the element
• ltmodtitlegtLaser4C (PR205)lt/modtitlegt

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ADDING ELEMENTS FROM THE MODELS VOCABULARY

• In the table cell directly after the Description
  table heading, insert the element
• ltmoddescriptiongtEntry level color laser
  printerlt/moddescriptiongt
• In the table cell directly after the Type table
  heading, insert the element
• ltmodtypegtcolor laserlt/modtypegt
• In the table cell directly after the Items to be
  Built table heading, insert the element
• ltmodorderedgt320lt/modorderedgt

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ADDING ELEMENTS FROM THE MODELS VOCABULARY