Filtering XML elements based on tokenized external pa

Hello --

I'm trying to do parameterized XSLT-based filtering to strip out
unwanted structure from an XML file. The XML file represents a graph
data structure along with some other metadata. Conceptually I want to
extract a subgraph from this data structure, but want to do so in an
upwards-compatible way such that any additional tags in the XML are
carried over to the resulting document. For example, given this XML
file:

<graph>
    <node id="alpha"/>
    <node id="beta"/>
    <node id="delta"/>
    <node id="gamma"/>
    <edge from="alpha" to="delta"/>
    <edge from="alpha" to="beta"/>
    <edge from="alpha" to="gamma"/>
    <edge from="beta" to="beta"/>
    <mymetadata id="123"/>
</graph>

Given the above simple graph data structure, I want to produce a
filtered version that only includes node elements (ideally both node and
edge elements) that match a given set of input parameters, as well as
any other tags that might be included (e.g. the mymetadata tag). I'd
ideally like to issue a call like this so that I integrate this w shell
scripts:

    xsltproc mytransform.xslt myfile.xml --param nodelist "alpha,beta"

And get this back:

<graph>
    <node id="alpha"/>
    <node id="beta"/>
    <edge from="alpha" to="beta"/>
    <edge from="beta" to="beta"/>
    <mymetadata id="123"/>
</graph>

I have two questions:

1. What is the best way to create a pattern match that is parameterized
based on the incoming nodelist? I'd like to flexible about delimeters
(e.g. have both "alpha,beta" and "alpha   ,   beta" work). I've tried
playing with tokenize from EXSLT but can't figure how to use the
resulting tokens to implement the filtering in a single-pass.

2. Is there a way to implement this to also include the alpha-gamma edge
and the gamma node, based on the partial edge match to "alpha"? I know
how to do this w multiple passes (e.g. by marking the edges, then the
nodes, then filtering) but was wondering if there was a nice one-pass
functional approach I've missed.

Thank you in advance for your time.

Ramon

_________________________________

Ramon M. Felciano
INGENUITY Systems, Inc.