About Namespace in XML
allows you to create your own elements and attributes. XML also allows developers
to combine XML document types. For example, you could embed into an XHTML document
elements from a document type that you created. The following would be an example
of embedding your own elements into an XHTML document, but theres a possible
problem; look at the bolded elements;
<IDOCTYPE html PUBLIC -//w3c//DTD
XHTML 1.0 Strict //EN
Http: // www.w3.org/TR/xhtml 1/DTD/
<html xmlns =http://www.w3.org/1999/xhtml>
<title>TCP/IP for Webmasters</title>
The bold lines illustrate the problem of element name conflicts. The first title
elements belongs to the XHTML document type; however, the next two title elements
belong to our own document type. The problem arises when the processor has to
decide what to do with them. How does the processor know which t I t l e element
is which? The answer is XML namespaces.
XML namespaces allow you to use
an element from one document type (such as an XML document) and embed it in another
document type (such as an XHTML document). Because namespaces uniquely identify
a set of elements that belongs to a given document type, they ensure that there
are no element name conflicts.
The namespace in the XML recommendation
document is seen as a complement to the XML specification and can be found at
www.w3.org/TR/REC-xml-names. The recommendation document defines a special syntax
to identify namespaces. The document defines how a collection of elements can
be given unique identifiers; therefore, no matter where an element is used, you
can be sure that it belongs to the namespace.
There are two ways to
define a namespace
Default namespace defines a name3space using the
xml ns attribute without a prefix, and all child elements are assumed to belong
to the defined namespace. XTHML uses the default namespace construct to define
the XHTML namespace.
Local namespace Defines a namespace using the xml
attribute with a prefix. When the prefix is attached to an element, its
assumed to belong to that namespaces
In both cases, you define a
namespace using the xmlns attribute. The attributes value is the name that
identifies the namespace. A namespace name can be a Uniform Resource Identifier
A URI can be a URL or a URN. Most times, you l find URLs
used. This may seem strange, but the namespace is only symbolic and does not point
to a document or schema. The value should be unique.
A default namespace
is considered to apply to the element where its declared and to all child
elements that are not assigned to another namespace. You define the namespace
as you would define an attribute.
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