The XML NameSpace

1
The XML NameSpace

• http//www.w3.org/TR/REC-xml-names

2
Motivation

• XML is extensible
• But, extensibility does not come free
• Extensibility must be managed to avoid conflicts
• Namespaces is a solution to help manage XML
  extensibility
• Example xml_example/chap04 two people extend
  the same document in incompatible ways
• bookmark.xml
• star_rating.xml
• pa_rating.xml
• star_pa_rating.xml

3
Motivation (Cont.)

• Problems in star_pa_rating.xml
• Software designed to operate with PA rating would
  be lost
• How to do with 4 stars rating?
• Ignore?
• No way to differentiate PA rating with Star
  rating
• Brute-force solution Use different names for the
  two rating
• qa_pa_rating.xml

4
Motivation (Cont.)

• Documents that contain multiple markup
  vocabularies pose problems of recognition and
  collision.
• Software modules need to be able to recognize the
  tags and attributes which they are designed to
  process, even in the face of "collisions"
  occurring when markup intended for some other
  software package uses the same element type or
  attribute name.
• These considerations require that document
  constructs should have universal names, whose
  scope extends beyond their containing document.
  This specification describes a mechanism, XML
  namespaces, which accomplishes this.

5
NameSpaces

• Introduced to solve the problem of name conflict!

6
Declaration

• ltelement xmlnsprefixnamespace_urigt
• lttitle xmlnsdchttp//purl.org/dcgt
• Default namespace
• ltelement xmlnsnamespace_urigt
• lttitle xmlnshttp//purl.org/dcgt
• Example namespace_bookmark.xml
• ltqaratinggt5 stars lt/qaratinggt
• A prefix is added before each element name
• A colon separates the name and the prefix
• The prefixes of default namespace can be omitted.

URI is unique!!!
7
Definition

• An XML namespace is a collection of names,
  identified by a URI reference, which are used in
  XML documents as element types and attribute
  names.
• URI references which identify namespaces are
  considered identical when they are exactly the
  same character-for-character.
• Note that URI references which are not identical
  in this sense may in fact be functionally
  equivalent.
• Examples include URI references which differ only
  in case, or which are in external entities which
  have different effective base URIs.

8
Names from XML NameSpaces

• Names from XML namespaces may appear as qualified
  names, which contain a single colon, separating
  the name into a namespace prefix and a local
  part.
• The prefix, which is mapped to a URI reference,
  selects a namespace.
• The combination of the universally managed URI
  namespace and the document's own namespace
  produces identifiers that are universally unique.
• Mechanisms are provided for prefix scoping and
  defaulting.
• An attribute-based syntax described below is used
  to declare the association of the namespace
  prefix with a URI reference
• Software which supports this namespace proposal
  must recognize and act on these declarations and
  prefixes.

9
Other Issues

• namespace_uri is used to identify the definition
  sources of element/attribute
• rff_ref.xml
• Different prefixs, but the same namespace
• Scope a namespace is valid for the element where
  it is declared and all the inside elements
• scoping.xml
• A namespace also can be associated with specific
  attributes.
• attribute.xml

10
Uniqueness of Attributes

• In XML documents conforming to this
  specification, no tag may contain two attributes
  which
• have identical names, or
• have qualified names with the same local part and
  with prefixes which have been bound to namespace
  names that are identical

11
Namespaces and DTD

• The prefix and the attributes for namespace
  declaration must be declared in the DTD
• dtd_namespace1.xml
• dtd_namespace2.xml
• It is dangerous to declare namespaces in an
  external DTD, because a non-validating parser
  might skip external DTDs