passing data between custom python nodes

Hi everyone,

I am working on a nodetree-addon for blender. I am just trying to figure out how to pass data through the nodetree. For example if I wanted to pass meshdata through several filters, how would I do that? Or in my specific case: how would I generate an XML file for an external render engine using the node editor? I guess I could somehow use NodeSocketString to generate hierarchical XML data from the tree?

I have worked through the tutorials and have a basic node collection with sockets , properties etc… running. But I can’t find anything about how to pass data between nodes. I also had a look at several other addons like sverchok, but they all seem pretty “chaotic” to me regarding these things.
When I export the XML file from a final “viewer-node” with a button to a “create-xml” operator. Would I “manually” traverse the node tree from that last node? Or is there some automatic mechanism using the nodesockets? for example the update function…

whats the best pratice here? because I could not find any documentation about this …

greetings, Tom