namespaces

[Avinash Mulye]

I am realy frustrated with namespaces.
Can anyone tell me a one stop solution to study namespaces. A web-site/page will be the best.
For example take a look at this -
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3schools.com"
xmlns="http://www.w3schools.com"
elementFormDefault="qualified">
What is the difference between the "xmlns:xs" ,
"targetNamespace" & "xmlns" ?
I mean why do they need 3 and what is each one for ?
PLEASE HELP.
Avinash.

[Avinash Mulye]

Take a look at the description that w3schools has given -
The <schema> element may contain some attributes. A schema declaration often looks something like this:
<?xml version="1.0"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://www.w3schools.com"
xmlns="http://www.w3schools.com"
elementFormDefault="qualified">
...
...
</xs:schema>

The following fragment:
xmlns:xs="http://www.w3.org/2001/XMLSchema"

indicates that the elements and data types used in the schema (schema, element, complexType, sequence, string, boolean, etc.) come from the "http://www.w3.org/2001/XMLSchema" namespace. It also specifies that the elements and data types that come from the "http://www.w3.org/2001/XMLSchema" namespace should be prefixed with xs: !!
This fragment:
targetNamespace="http://www.w3schools.com"

indicates that the elements defined by this schema (note, to, from, heading, body.) come from the "http://www.w3schools.com" namespace.
This fragment:
xmlns="http://www.w3schools.com"

indicates that the default namespace is "http://www.w3schools.com".
This fragment:
elementFormDefault="qualified"

indicates that any elements used by the XML instance document which were declared in this schema must be namespace qualified.
_________________________________________________
Mark it -
xmlns="http://www.w3schools.com" indicates that the default namespace is
"http://www.w3schools.com"
What does this mean !!!
Once you specify a namespace the why do you need default one ?
This is nightmare !
PLEASE HELP.
Avi

[Shoba Ramachandran]

Hi,
Check out the tutorial at www.xfront.com which has good stuff about schemas
-Shoba

[Danl Thompson]

Namespaces, they say, are simple. However, I find them not. To my mind, a simple one page NS overview is out of the question.
NS may be applied to elements, attributes, and data-types. However, just because a name has a colon : in it, doesn't put it in a NS. On the other hand, a name without a : may still be in an NS. Oddly, colon is a valid starting character for names.
Elements with the same local name but different NS can co-exist in the same document. However, Attributes with the same local name, but different NS prefixes cannot co-oexist in the same Element.
NS definitions in Schemas are complicated by the schema attributes, targetNamespace, elementFormDefault, and attributeFormDefault, includes, imports, and redefines.
And NS prefixes don't mean much. I once thought the prefix WAS the NS, and that the URL was meaningless. But I was wrong.
So, there is much to learn, to mull over, and so forth, regarding NS. Learn slowly, and retain it all.