XPath Support for EMF

About

The goal of this project is to provide support for using the XPath language to navigate arbitrary Eclipse Modeling Framework (EMF) models. Jaxen is used as the underlying XPath engine, with a custom document model adapter that allows it to navigate EMF object graphs using XPath constructs. Because XPath works with tree-based document structures, EMF's containment hierarchy is used as the basis for the mapping:

EObjects expose their structural features as XML elements
Feature maps are not exposed directly, only their entries
Each feature value is exposed as a sub-element named after the feature; multi-valued features have an element for each individual value
The element's namespace is the namespace of the feature's declaring package
Only non-null values are exposed
There are no XML attributes (the attribute axis is supported, but will always be empty)
Elements representing attribute features have a single child text node with the feature value converted to its string representation
Elements representing containment references further expose their structural features (as described above)
Elements representing non-containment references do not (i.e., they have no child elements); you can use the contents(nodeset?) function to expose a reference's (the function's argument, or taken from the current context) contents
In addition, both containment and non-containment reference elements have a child text node with their URI as determined by EcoreUtil.getURI(EObject)
The model's document node is its ResourceSet, or the Resource, or the root container (EcoreUtil.getRootContainer(EObject))
ResourceSet nodes have a resources sub-element for each Resource they contain
Resource nodes have a contents sub-element for each object they contain, as well as a text node with their URI (if non-null)
Function eClass(nodeset?) exposes the argument's (or current context's) metamodel

For instance, using the example Library model referenced in EMF tutorials, XPath expression /resources/contents/lib:books would designate all books in the library. Expression lib:books[lib:author=current()/lib:writers[lib:name='John Grisham']] designates those library books whose author's name is John Grisham. Note that the lib prefix must be bound to Library's namespace. E.g.,

EMFXPath xpath = new EMFXPath("lib:books[lib:author=current()/lib:writers[lib:name='John Grisham']]"); xpath.addNamespace("lib", LibraryPackage.eNS_URI); List books = xpath.selectNodes(library);

Note that this navigation model does not necessarily match the DOM model generated by EMF's XML persistence mechanism. In fact, the models need not be persisted in XML at all in order to be used with EMFXPath. Those who wish to evaluate XPath expressions against a literal XML representation of their EMF models should try an alternative XPath evaluator implemented in class EMFDOMXPath (experimental).

Class EMFXPath provides a helper static method dump(Object, OutputStream), which traverses the given object, converts it to XML and writes it out into the output stream. This is especially useful for debugging -- it essentially shows the model from the navigator's point of view (i.e., how EMFXPath sees it). For instance, an example Library model with two writers and three books might look like this:

<resources>
   <contents>
      <library:name>Test Library</library:name>
      <library:writers>
         <library:name>Writer 1</library:name>
         <library:books>test.library#/0/@books.0</library:books>test.library#/0/@writers.0</library:writers>
      <library:writers>
         <library:name>Writer 2</library:name>
         <library:books>test.library#/0/@books.1</library:books>
         <library:books>test.library#/0/@books.2</library:books>test.library#/0/@writers.1</library:writers>
      <library:books>
         <library:title>Book 1</library:title>
         <library:pages>1000</library:pages>
         <library:category>Mystery</library:category>
         <library:author>test.library#/0/@writers.0</library:author>test.library#/0/@books.0</library:books>
      <library:books>
         <library:title>Book 2</library:title>
         <library:pages>2000</library:pages>
         <library:category>ScienceFiction</library:category>
         <library:author>test.library#/0/@writers.1</library:author>test.library#/0/@books.1</library:books>
      <library:books>
         <library:title>Book 3</library:title>
         <library:pages>3000</library:pages>
         <library:category>Biography</library:category>
         <library:author>test.library#/0/@writers.1</library:author>test.library#/0/@books.2</library:books>test.library#/0</contents>test.library</resources>

Download

The latest release (2.0.0) is a complete rewrite of the navigation model. It was compiled using Eclipse 3.2.1, EMF 2.2.1, and JRE 1.4.2. The latest Jaxen distribution (v1.1) is included.

Package	Description
emf-xpath-2.0.0.zip	Binary feature
emf-xpath-SDK-2.0.0.zip	SDK feature with source and unit tests

Alternatively, you can point your Eclipse Update Manager to this project's update site at http://www.eclipticalsoftware.com/updates.

This software is made available under the terms of the Eclipse Public License v1.0.