Some beginner's questions

Hi all,
I'm using XSD schema to perform validation about any XML document belonging to an archive of documents.

Almost all of the document is invariable so the application simply extracts it from the archive. A small part, however, is highly variable because needs an operator to supply decisions and data that will be integrated into the document in some structure based on proper XSD types.

Two questions:

1. The layout of the variable part depends on some other information pertinent to XML elements of the document. How can I specify this constrain ?

<Message id="19">
...
    <Information>
        <Text>...</Text>
        <Data ...>...</Data>
    </Information>
...
</Message>

Based on the value of the attribute "id" the layout of the element Data can vary.


2. Once I have the document I can validate some its elements against a XSD Schema. Can I *generate* an XML document or fragment from a XSD schema, with some external decisions provided by the application ? If yes how must the schema be structured ?

Thanks

S. Troiani