[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] Using XSLT and XPath for graph data structure processing?
Helo all -- I'm trying to gain a deeper understand for what type of semi-declarative programming can be done through XML and XPath/XSLT. I'm looking at graph processing problems as a testbed for this, and came across a problem that I haven't been able to solve elegantly. The problem is to find "linker" vertexes that a pair of verteces from a pre-defined set. For example, if the graph verteces represent cities and edges represent flights between them, then given a list of cities, find all intermediate cities that you would stop in via a "connecting flight". For example, given the following simple graph: V1 -> V2 -> V3 -> V4 \<- V5 ->/ (V5 points to both V2 and V4), and its XML serialization: <graph> <vertex id="V1"/> <vertex id="V2" type="anchor"/> <vertex id="V3"/> <vertex id="V4" type="anchor"/> <vertex id="V5"/> <edge source="V1" target="V2"/> <edge source="V2" target="V3"/> <edge source="V3" target="V4"/> <edge source="V5" target="V2"/> <edge source="V5" target="V4"/> </graph> I would like to transform this into a second graph where all vertexes that "link" two anchor distinct vertexes are flagged as link nodes. In this case, there are two anchor vertexes V2 and V4, and I can link them through V3 (V2 -> V3 -> V4) and V5 (V2 <- V5 -> V4). Note that linked verteces must be distinct, so traversing the V2 <- V1 -> V2 path should not yield V1 as a link node. So I'd like to see something like this: <graph> <vertex id="V1"/> <vertex id="V2" type="anchor"/> <vertex id="V3" linker="true"/> <vertex id="V4" type="anchor"/> <vertex id="V5" linker="true"/> <edge source="V1" target="V2"/> <edge source="V2" target="V3"/> <edge source="V3" target="V4"/> <edge source="V5" target="V2"/> <edge source="V5" target="V4"/> </graph> It would be ideal to come up with a generalized solution that would let you use 1, 2, .. N intermediate linking nodes. I've been able to get this working with nested loops, but it isn't particularly declarative or speedy, and is certainly more verbose than I'd like, so I'm wondering if anyone here has insights into how to do this elegantly and in XSLT/XPath style. For example, is it possible to write a single XPath expression that will select <vertex> elements that obey the above criteria? If not, does anyone have any suggestions for how to code this effectively and efficiently with XSLT? Thanks! Ramon
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