Philippe Poulard wrote:

> Bob Smith wrote:
>> hi all,
>> I pretty new to xml, what does xmlns mean?
>> like in:
>> <rdf:RDF
>>  xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
>>  xmlns="http://purl.org/rss/1.0/"
>>  xmlns:perljobs="http://jobs.perl.org/rss/"
>>  xmlns:taxo="http://purl.org/rss/1.0/modules/taxonomy/"
>>  xmlns:dc="http://purl.org/dc/elements/1.1/"
>>  xmlns:syn="http://purl.org/rss/1.0/modules/syndication/"
>>  xmlns:admin="http://webns.net/mvcb/"
>> 
>> tia
> 
> xmlns is used to bound prefixes to namespace URIs
> 
> it means that the *universal name* of the <rdf:RDF> element is
> [ http://www.w3.org/1999/02/22-rdf-syntax-ns# , RDF ]
> this notation [ URI , local-name ] denotes that the *universal name* is
> in 2 parts (in most XML papers, it is displayed with another notation :
> {http://www.w3.org/1999/02/22-rdf-syntax-ns#}RDF but I prefer the
> former) ; notice that these notations are only for explanation and NEVER
> appear in real XML documents
> 
> such names are *universal names* because URIs are unique ; notice that
> an URI is not necessary an URL :
> xmlns:foo="urn:guid:88d969c9-f192-11d4-a65f-0040963251e6"
> xmlns:book="urn:isbn:2-84177-230-6"
> xmlns:office="urn:schemas-microsoft-com:office:office"
> namespace URIs are just use to qualify XML names
> 
> the prefix is just an alias for the URI, but its mean is local to the
> xmlns declaration (that is to say, applies on its host element and its
> descendents)
> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
> <foo:RDF xmlns:foo="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
> <RDF xmlns="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
> are the same ; the last form doesn't use a prefix, it uses the default
> namespace
> 
> attributes are told "owned" by their host elements, so they don't need
> additional information ; that's why the default namespace doesn't apply
> to attributes ; sometimes, it is necessary to "add" to an element
> special purpose attributes, that are often called "foreign attributes" :
> <image xmlns:xlink="http://www.w3.org/1999/xlink">
>         xlink:type="simple"
>         xlink:actuate="onLoad"
>         xlink:show="embed"
>         xlink:href="http://www.acme.com/foo/bar.jpg"
>         width="123"
>         height="234" />
> 
> some application may recognize a particular namespace URI :
> -for example, an application might expose an hyperlink in conformance to
> the XLink specification if it encounters attributes like those above
> -an XSLT processor will do something special when it encounters
> <xsl:template> not because the prefix is "xsl" but because this element
> is in the scope of the xmlns declaration :
> xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
> -a graphic application that recognize SVG could draw a rectangle :
> <svg:svg xmlns:svg "http://www.w3.org/2000/svg"
>      width="18cm" height="6cm" viewBox="0 0 200 120">
>          <svg:rect x="1" y="1" width="198" height="118"
>                    fill="#888888" stroke="blue" />
> </svg:svg>
> 
> if you have to design XML datas, I encourage you to use your own
> namespace URI with your elements : thus, your application will be able
> to process these elements without ambiguity ; XML namespaces have been
> design for that purpose : distinguish elements that could have the same
> local name, and grouping a set of names "related to the same feature"
> 
T H A N K ... Y O U !!!!!!!!!!!!!
:-)
-- 
http://www.kolumbus.fi/bob.smith