net.sf.saxon.expr

Class Optimizer

public class Optimizer extends Object implements Serializable

This class doesn't actually do any optimization itself, despite the name. Rather, it is intended to act as a factory for implementation classes that perform optimization, so that the appropriate level of optimization can be selected.

Field Summary
protected Configuration	config

Constructor Summary
	Optimizer(Configuration config)

Method Summary
Expression	convertPathExpressionToKey(PathExpression pathExp, StaticContext env) Examine a path expression to see whether it can be replaced by a call on the key() function; if so, generate an appropriate key definition and return the call on key().
FilterExpression	convertToFilterExpression(PathExpression pathExp, TypeHierarchy th) Convert a path expression such as a/b/c[predicate] into a filter expression of the form (a/b/c)[predicate].
Configuration	getConfiguration()
int	isIndexableFilter(Expression filter) Test whether a filter predicate is indexable.
Closure	makeClosure(Expression expression, int ref) Make a Closure, given the expected reference count
BinaryExpression	makeGeneralComparison(Expression p0, int op, Expression p1, boolean backwardsCompatible) Create a GeneralComparison expression
Expression	optimizeCopy(Expression select) Attempt to optimize a copy operation.
SequenceIterator	tryIndexedFilter(ValueRepresentation startValue, Expression filter, int isIndexable, XPathContext context)

Field Detail

config

protected Configuration config

Constructor Detail

Optimizer

public Optimizer(Configuration config)

Method Detail

convertPathExpressionToKey

public Expression convertPathExpressionToKey(PathExpression pathExp, StaticContext env)

Examine a path expression to see whether it can be replaced by a call on the key() function; if so, generate an appropriate key definition and return the call on key(). If not, return null.

Parameters: pathExp The path expression to be converted.

convertToFilterExpression

public FilterExpression convertToFilterExpression(PathExpression pathExp, TypeHierarchy th)

Convert a path expression such as a/b/c[predicate] into a filter expression of the form (a/b/c)[predicate]. This is possible whenever the predicate is non-positional. The conversion is useful in the case where the path expression appears inside a loop, where the predicate depends on the loop variable but a/b/c does not.

Parameters: pathExp the path expression to be converted

Returns: the resulting filterexpression if conversion is possible, or null if not

getConfiguration

public Configuration getConfiguration()

isIndexableFilter

public int isIndexableFilter(Expression filter)

Test whether a filter predicate is indexable.

Parameters: filter the predicate expression

Returns: 0 if not indexable; +1 if the predicate is in the form expression=value; -1 if it is in the form value=expression

Parameters: select the expression that selects the items to be copied

Returns: null if no optimization is possible, or an expression that does an optimized copy of these items otherwise

tryIndexedFilter

public SequenceIterator tryIndexedFilter(ValueRepresentation startValue, Expression filter, int isIndexable, XPathContext context)