one xml file + one xsl file => user based output

Hello!
I'm a student at the Salzburg University, and have the
following problem:
We have to implement a system, which is able to
generate html pages dynamically.
We have xml, xsl and cocoon available, and have to use
them to achieve a user/profile based transformation of
an xml file to html file. This means that
depending on the group to which the user belongs to,
the html file will be generated. We have three groups
of users: adiministrators, professors and students.
There must be only one xml file, containing all
information. We thought about the following xml file
structure:
                   <document>
                      <section>
                           <admin>
                             ...
                                   <professor>
                                   .....
                                           <student>
                                            ......
                                           </student>
                                   ....
                                   </professor>
                           .....
                           </admin>
                      </section>

                      <section>
                        .
                        .
                      </section>
                        .
                        .
                        .
                   </document>

since the admin should get all of the information from
the file available, professor should get less, and a
student the least. 

Is there a way to generate a user(group) specific html
output by means of one xml and one xsl file?  
Is there a way to pass parameters to xsl file, before
transformation?

 Any help is appreciated!
 Zenina

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