xml-dev - Re: XML Schemas

[Len Bullard <cbullard@hiwaay.net>]

Veena Rao wrote:
> 
> Is it always necessary to use and specify a XML Schema in an
> XML document that needs to be parsed. 

No.  You can use a DTD to validate the structure and the limited 
XML datatypes, or you can simply use a well-formed parse limited 
to the syntax and reserved productions.

> Won't it be sufficient to
> have it validated against a XMLSchema DTD.

In many cases, yes.  It depends on your model.  That is, what 
are you using the XML format for, persistence, data binding, 
exchange?  A DTD works well for authoring where you want to 
control the structures being created and you want to use 
an extensible editor, and it works well when you are 
exchanging information among loosely coupled systems or 
blind exchanges.  The xsd or schema is more powerful but 
also, you have to ask if you want to use information in this 
form to constrain the system.  See below.
 
> I am trying to find out if I can get away without generating a .xsd
> for every object model that is used within our application server.

You can.  In X3D for example, although there is a DTD (several 
in fact) and an example of an XML schema, most of the vendors do 
not use them at runtime.  They choose in most cases, an object model 
and a context-free parse.  A lot depends on how much overhead 
you can support at runtime.
 
len


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