xmlns :mama="http://mamazon.com/schema" xmlns

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Let’s take a closer look at what’s going on:
xmlns
:mama="http://mamazon.com/schema"
xmlns
:nab="http://NarnesAndBobel.com/book.dtd"
xmlns
:e_com_org="http://e_com_org.com/schema">
Our root element is 
Results
.
The xmlns keyword is part of the reserved vocabulary in XML used for declaring the 
namespace prefix
(in this case mama, nab, and e_com_org) and the location (a UUID, 
URN, URI, or URL) of the respective DTD or schema. 
 
UUID, URN, and URI
All of these are ways of representing the complete address and route for locating a 
file across electronic networks.
A UUID is a Universally Unique IDentifier. It is similar to a GUID (Globally Unique 
IDentifier), which is used for identifying COM (Component Object Model) objects. 
A URN is a Uniform Resource Name. It defined by the IETF (Internet Engineering 
Task Force) as “resource identifiers with the specific requirements for enabling 
location independent identification of a resource, as well as longevity of reference.” 
Simply put, they provide permanent, unique addresses for files over a network. 
A URI is a Uniform Resource Identifier. The IETF defines a URI as a scheme that 
allows resources to be uniquely named over time and space using Universally 
Unique Identifiers (UUIDs). It consists of a series of characters.
 
The namespace prefix mama is used to distinguish every attribute and element whose 
description (document type definition) comes from the 
http://mamazon.com/schema
file. 
The namespace prefix nab is used to distinguish every attribute and element whose 
description comes from the DTD file located at 
http://NarnesAndBobel.com/book.dtd
. 
Similarly, the prefix e_com_org is used to describe standard elements and attributes that 
are defined by the mythical E-commerce Organization.
The xmlns: attribute’s value is the location of the DTD or schema. The parser goes to 
those locations, reads through their definitions, and commits them to memory so that 
whenever an element or attribute bearing the namespace prefix appears in the Results 
element, it is validated against the respective DTD or schema.
The region or 
scope
where you can use elements and attributes of the types defined in 
the given schemas and DTD is limited to the child elements and attributes of the Results 
element. This is called scoping
the namespace. You could locally scope the namespaces 
by assigning the xmlns: keyword in each element, but the following is a much more 
efficient way of doing this:

Here we’re using a book element whose definitions are described in the 
http://mamazon.com/schema
file. When parsed to check for validity, the parser checks 
this element against the type definitions expressed in the schema. Thus, the rest of the 
book element’s structure has to look exactly like it would if it were working in isolation. 

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We’ve prefixed all the mama:book elements with the mama prefix to tell the parser that 
each component used is to be validated against the Mamazon.com schema.
2.75
We’re trying to illustrate that it is possible to use components described across many 
different schemas and DTDs. Here, we’ve made up a mythical electronic commerce 
organization that globally defines standards for currency units. While the mama:price 
element is subject to validation against Mamazon’s schema, its currency attribute is 
subject to validation against the E-commerce Organization’s schema.
Also, we should clarify that we’re assuming that the mama schema has a provision for 
allowing a currency attribute in it whose definition comes from the E-commerce 
Organization.

Here we’re using a book element whose definitions are described in the 
http://NarnesAndBobel.com/book.dtd
file. When this element is parsed to check for 
validity, the parser checks it against the type definitions expressed in that DTD. Thus, the 
rest of the nab:book element’s structure—in this case its attributes—have to look exactly 
as it would if it were working in isolation. We’ve prefixed all of the nab:book attributes with 
the nab prefix to tell the parser that each component used is to be validated against the 
NarnesAndBobel DTD.

You should buy the book from Mamazon.com

Wait a minute; these elements don’t have any prefixes! That’s fine. Remember that you 
don’t 
have
to validate everything. In this case, because this element is our own and we 
have control over it, we decided not to validate it against anything. Our Result element is 
not limited to only containing elements and attributes defined in the xmlns: attribute 
values.

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