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Composable Lazy Tree Model

Added by Anonymous over 13 years ago

Legacy ID: #10502855 Legacy Poster: Paul Duffin (paulduffin)

I have a data structure (not XML) which is organized as a DAG. I want to apply XSLT to an XML representation of an item in that data structure in order to generate HTML presentation of that item. However, the item can reference other items in the graph but I do not want to flatten the graph into XML at the start (there are possibly millions of items in the graph). So what I need is a tree model that when the contents of a specific node (a reference to another item) is requested that it calls me back to get the XML representation of that. I also want to share the basic unexpanded tree model for each item so that once it has been generated I can use it again either directly or referenced from another item. Is there any support for that in Saxon? Is it something that Saxon is capable of handling? I noticed a reference to http://www.nesterovsky-bros.com/weblog/2010/04/08/ComposableTreeModelInSaxon.aspx from within this forum and wondered whether anything similar had been done.


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RE: Composable Lazy Tree Model - Added by Anonymous over 13 years ago

Legacy ID: #10502977 Legacy Poster: Michael Kay (mhkay)

Saxon allows you to write your own implementation of the NodeInfo interface, and supply a tree using that implementation as a source document, or as the result of calling the doc() function (or a Java extension function). So long as the implementation satisfies the NodeInfo contract, it should work. The "contract" here is not only the Java API, but also the constraints and consistency rules in the XDM specification, for example the fact that the string value of an element must be the concatenation of its descendant text nodes, that you can't have a zero-length text node with a parent, that the namespace of an attribute must be one of the in-scope namespaces of the containing element, and so on. I have implemented NodeInfo over a variety of data structures; the more they deviate from XML, the harder it gets. But it can certainly be done. Note that with the NodeInfo interface, it is not assumed that Java object identity equates to XDM node identity. The "same" XDM node can be represented by different NodeInfo objects at the same time or at different times.

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