Is there a XPath Expression that returns the DocumentType (dtd/schema)
of an xml document ?

Also, when trying to call namespace-uri(nodeset-expression) with a null
argument using Java API, is it right to
assume that I will always get the namespace-uri of the document node ?

Following is the code snippet I'm using to evaluate XPath Expressions
from Java.:

        builder = ((Controller)transformer).makeBuilder();
        if (builder != null)
            docInfo = builder.build(ss);
        if (docInfo != null)
             context = ((Controller)transformer).makeContext(docInfo);
        NamePool namepool = ((Controller)transformer).getNamePool();
        if (namepool != null)
             sctx = new StandaloneContext(namepool);

        //Evaluate xpathExpression
        if (xpathExpression != null)
            Expression expr = Expression.make(xpathExpression, sctx);
            Value val = expr.evaluate(context);