net.sf.saxon.expr
Class PathMap

java.lang.Object
  net.sf.saxon.expr.PathMap

public class PathMap
extends 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, net.sf.saxon.expr.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.

Nested Class Summary

static class	PathMap.PathMapArc An arc joining two nodes in the path map.
static class	PathMap.PathMapNode A node in the path map.
static class	PathMap.PathMapNodeSet A (mutable) set of nodes in the path map
static class	PathMap.PathMapRoot A root node in the path map.

Constructor Summary

PathMap(Expression exp)
Create the PathMap for an expression

Method Summary

void	diagnosticDump(PrintStream out) Display a printed representation of the path map
PathMap.PathMapRoot	getContextRoot() Get the path map root for the context document
PathMap.PathMapNodeSet	getPathForVariable(Binding binding) Get the path used when evaluating a given variable binding
PathMap.PathMapRoot[]	getPathMapRoots() Get all the root expressions from the path map
PathMap.PathMapRoot	getRootForDocument(String requiredUri) Get the path map root for a call on the doc() or document() function with a given literal argument
static void	main(String[] args) Main method for testing
PathMap.PathMapRoot	makeNewRoot(Expression exp) Make a new root node in the path map.
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.
void	registerPathForVariable(Binding binding, PathMap.PathMapNodeSet nodeset) Register the path used when evaluating a given variable binding

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

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

getContextRoot

public PathMap.PathMapRoot getContextRoot()

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:

IllegalStateException - if there is more than one path map root for the context document

getRootForDocument

public PathMap.PathMapRoot getRootForDocument(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:

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

diagnosticDump

public void diagnosticDump(PrintStream out)

Display a printed representation of the path map

Parameters:

out - the output stream to which the output will be written

main

public static void main(String[] args)
                 throws Exception

Main method for testing

Parameters:

args - Takes one argument, the XPath expression to be analyzed

Throws:

Exception