Package net.sf.saxon.expr.parser

Class PathMap

  • public class PathMap
extends java.lang.Object
    A PathMap is a description of all the paths followed by an expression. It is a set of trees. Each tree contains as its root an expression that selects nodes without any dependency on the context. The arcs in the tree are axis steps. So the expression doc('a.xml')/a[b=2]/c has a single root (the call on doc()), with a single arc representing child::a, this leads to a node which has two further arcs representing child::b and child::c. Because element b is atomized, there will also be an arc for the step descendant::text() indicating the requirement to access the text nodes of the element.

    The current implementation works only for XPath 2.0 expressions (for example, constructs like xsl:for-each-group are not handled.)

    This class, together with the overloaded method Expression.addToPathMap(PathMap, PathMap.PathMapNodeSet) can be seen as an implementation of the static path analysis algorithm given in section 4 of A. Marian and J. Simeon, Projecting XML Documents, VLDB 2003.

    • Constructor Detail

      • PathMap

        public PathMap​(Expression exp)
        Create the PathMap for an expression
        Parameters:
        exp - the expression whose PathMap is required

    • Method Detail

      • makeNewRoot

        public PathMap.PathMapRoot makeNewRoot​(Expression exp)
        Make a new root node in the path map. However, if there is already a root for the same expression, the existing root for that expression is returned.
        Parameters:
        exp - the expression represented by this root node
        Returns:
        the new root node

      • getPathMapRoots

        public PathMap.PathMapRoot[] getPathMapRoots()
        Get all the root expressions from the path map
        Returns:
        an array containing the root expressions

      • registerPathForVariable

        public void registerPathForVariable​(Binding binding,
                                    PathMap.PathMapNodeSet nodeset)
        Register the path used when evaluating a given variable binding
        Parameters:
        binding - the variable binding
        nodeset - the set of PathMap nodes reachable when evaluating that variable

      • getPathForVariable

        public PathMap.PathMapNodeSet getPathForVariable​(Binding binding)
        Get the path used when evaluating a given variable binding
        Parameters:
        binding - the variable binding
        Returns:
        the set of PathMap nodes reachable when evaluating that variable

      • getContextDocumentRoot

        public PathMap.PathMapRoot getContextDocumentRoot()
        Get the path map root for the context document
        Returns:
        the path map root for the context document if there is one, or null if none is found.
        Throws:
        java.lang.IllegalStateException - if there is more than one path map root for the context document

      • getContextItemRoot

        public PathMap.PathMapRoot getContextItemRoot()
        Get the path map root for the context item
        Returns:
        the path map root for the context item if there is one, or null if none is found.
        Throws:
        java.lang.IllegalStateException - if there is more than one path map root for the context item

      • getRootForDocument

        public PathMap.PathMapRoot getRootForDocument​(java.lang.String requiredUri)
        Get the path map root for a call on the doc() or document() function with a given literal argument
        Parameters:
        requiredUri - the literal argument we are looking for
        Returns:
        the path map root for the specified document if there is one, or null if none is found.
        Throws:
        java.lang.IllegalStateException - if there is more than one path map root for the specified document

      • reduceToDownwardsAxes

        public PathMap.PathMapRoot reduceToDownwardsAxes​(PathMap.PathMapRoot root)
        Given a PathMapRoot, simplify the tree rooted at this node so that it only contains downwards selections: specifically, so that the only axes used are child, attribute, namespace, and descendant. If the root expression is a ContextItemExpression (that is, the path can start at any node) then it is rebased to start at a root node, which means in effect that a path such as a/b/c is treated as //a/b/c.
        Parameters:
        root - the root of the path to be simplified
        Returns:
        the path map root after converting the tree to use downwards axes only