Package com.saxonica.ee.trans

Class PreconditionMatcher

java.lang.Object
net.sf.saxon.trans.rules.RuleSearchState
com.saxonica.ee.trans.PreconditionMatcher
public class PreconditionMatcher extends RuleSearchState
This class contains the stateful part of the precondition checker. A new PreconditionMatcher is allocated when searching a rule chain to find the best matching rule for a given node (or other item). It holds the values of preconditions and characteristics. A precondition is a boolean property of an item that must be true if the item is to match a particular pattern; once the precondition has been evaluated, its value can be used to eliminate other rules with the same precondition. A characteristic is a property of an item that must match a corresponding property of a rule if the rule is to match; for example, a property might be "name of parent element". Once the value of a characteristic (for example, the name of the parent element) has been evaluated, a rule can be eliminated if it requires a different value for the characteristic.

  • Constructor Details

    • PreconditionMatcher

      public PreconditionMatcher(RuleChain chain, XPathContext context)
      Allocate a PreconditionMatcher for a given set of rules
      Parameters:
      chain - the set of rules being matched
      context - the XPath evaluation context; the context item is the item being matched against the set of rules

  • Method Details

    • getPreconditionState

      public int getPreconditionState(int slot)
      Get the state of a given precondition.
      Parameters:
      slot - the slot number allocated to the precondition
      Returns:
      Precondition.PRECONDITION_TRUE if the precondition is known to be true for the item being matched; Precondition.PRECONDITION_FALSE if it is known to be false; or Precondition.PRECONDITION_UNKNOWN if its value is not known

    • setPreconditionState

      public void setPreconditionState(int slot, boolean value)
      Set the value of a given precondition.
      Parameters:
      slot - the slot number allocated to the precondition
      value - true if the precondition (for the item being matched) is known to be true, false if it is known to be false.

    • checkPreconditions

      public boolean checkPreconditions(Rule rule) throws XPathException
      Use this search state to check whether the preconditions for a particular rule are satisfied
      Overrides:
      checkPreconditions in class RuleSearchState
      Parameters:
      rule - the rule being tested
      Returns:
      true if all preconditions are satisfied; in the HE implementation, there are no preconditions, so this is always true.
      Throws:
      XPathException - if evaluation of preconditions fails.

    • obtainCharacteristic

      public Object obtainCharacteristic(Characteristic chic) throws XPathException
      Get the value of a particular characteristic of the item being matched, evaluating it if it has not already been evaluated, and retaining its value for future use
      Parameters:
      chic - the characteristic to be evaluated
      Returns:
      the value of the characteristic
      Throws:
      XPathException - if evaluation of the characteristic failed