Package net.sf.saxon.expr.parser
Class PathMap
java.lang.Object
net.sf.saxon.expr.parser.PathMap
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.
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Nested Class Summary
Nested ClassesModifier and TypeClassDescriptionstatic class
An arc joining two nodes in the path map.static class
A node in the path map.static class
A (mutable) set of nodes in the path mapstatic class
A root node in the path map. -
Constructor Summary
Constructors -
Method Summary
Modifier and TypeMethodDescriptionGet the path map root for the context documentGet the path map root for the context itemgetPathForVariable
(Binding binding) Get the path used when evaluating a given variable bindingGet all the root expressions from the path mapgetRootForDocument
(String requiredUri) Get the path map root for a call on the doc() or document() function with a given literal argumentmakeNewRoot
(Expression exp) Make a new root node in the path map.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
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Constructor Details
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Method Details
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makeNewRoot
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
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getPathMapRoots
Get all the root expressions from the path map- Returns:
- an array containing the root expressions
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registerPathForVariable
Register the path used when evaluating a given variable binding- Parameters:
binding
- the variable bindingnodeset
- the set of PathMap nodes reachable when evaluating that variable
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getPathForVariable
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
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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:
IllegalStateException
- if there is more than one path map root for the context document
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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:
IllegalStateException
- if there is more than one path map root for the context item
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getRootForDocument
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
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reduceToDownwardsAxes
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
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