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Eclipse JET Guide
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Essential XPath

JET implements the W3C XPath 1.0 Specification, with a few minor exceptions. Although the XPath language is rich, there are only a small part of the XPath language that is required to use most JET tags.

XPath (and JET) assumes that it is working on a model that has a tree structure. While this certainly include XML documents (the X in XPath), it can include many other kinds of models as well. Out of the box, JET supports XML documents and any model that is represented by EMF. (See Eclipse Modeling Framework).

A major element of XPath is the path expression. These are similar to file system paths.

  • An path is a series of steps separated by forward slashes (/).
  • The steps are evaluated from left to right, and generally decend the model's tree as they do so.
  • Each step generally identifies tree nodes by their name (although other possibilities exist).
  • Steps may have an optional filter condition which is written in square brackets ([ and ]) at the end of the step.
  • An initial slash (/) indicates an expression starts at the root of the model tree.
  • Path expressions can also start with a variable, which is a name preceded by a dollar sign ($).

XPath also supports general mathematical, boolean and comparison expressions as well as function calls.

JET tags that use XPath expressions have common characteristics:

  • Variables are defined by several JET tags - look for a var attribute. They may also be defined by the c:setVariable tag.
  • JET tags requiring a path expresion have a select attribute.
  • JET tags requiring a boolean expression have a test.
  • Any tag attribute may include a dynamic XPath expression - an XPath expression surrounded by braces ({ and }).

The following tutorials provide a quick introduction to XPath expressions. The first tutorial allows you to type expressions, and see their results!


 
 
  Published under the terms of the Eclipse Public License Version 1.0 ("EPL") Design by Interspire