com.hp.hpl.jena.graph.query
Class QueryNode

java.lang.Object
  com.hp.hpl.jena.graph.query.QueryNode

Direct Known Subclasses:

QueryNode.Any, QueryNode.Bind, QueryNode.Bound, QueryNode.Fixed, QueryNode.JustBound

public abstract class QueryNode
extends Object

A QueryNode is a wrapped node that has been processed against some variable-binding map to discover (a) what kind of node it is and (b) what index in the binding map it has.

There are five sub-classes of QueryNode

• Fixed - a concrete node, with pseudo-index NO_INDEX
• Bind - a variable node's first, binding, appearance
• JustBound - a variable node's bound appearance in the same [triple] context as its binding appearance
• Bound - a variable node's bound appearance
• Any - Node.ANY (or, in principle, a free variable)

Author:

hedgehog

Nested Class Summary

static class	QueryNode.Any
static class	QueryNode.Bind
static class	QueryNode.Bound
static class	QueryNode.Fixed
static class	QueryNode.JustBound
class	QueryNode.MustNotMatchException Internal exception to throw if, against all chance, something that shouldn't be involved in a match is.

Field Summary

static QueryNodeFactory	factory
int	index The index value allocated to this query node; NO_INDEX except for a variable node, in which case it is the allocated index in the domain object.
static int	NO_INDEX Fake index value to use when no index makes sense; we choose a value that will fail any array-bound check if it happens to be used anyway.
Node	node The Node value on which this QueryNode is based.

Method Summary

static QueryNode	classify(QueryNodeFactory f, Mapping map, Set<Node> recent, Node n) Answer a QueryNode that classifies the argument node n.
Node	finder(Domain d) Answer a Node value to use when this QueryValue is used to select objects in a Graph::find() operation; for concrete nodes, that very node, for variables their current value (ANY if not bound).
boolean	isFrozen() Answer true iff this node is "frozen", ie its value is fixed, when it is encountered; that is, it is not a Bind or JustBound node.
boolean	match(Domain d, Node x) Answer true iff this QueryNode matches, in the context of the binding Domain d, the node x.
abstract boolean	matchOrBind(Domain d, Node x) Optimisation: the action to be performed when matching a just-bound variable or binding a newly-bound variable, or nothing for any other kind of QueryNode.
boolean	mustMatch() Answer true iff this QueryNode must be used in a triple-match of its owning QueryTriple.
String	toString() Return a handy string representation for debugging purposes.

Methods inherited from class java.lang.Object

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

Field Detail

NO_INDEX

public static final int NO_INDEX

Fake index value to use when no index makes sense; we choose a value that will fail any array-bound check if it happens to be used anyway.

See Also:

Constant Field Values

node

public final Node node

The Node value on which this QueryNode is based.

index

public final int index

The index value allocated to this query node; NO_INDEX except for a variable node, in which case it is the allocated index in the domain object.

factory

public static final QueryNodeFactory factory

Method Detail

toString

public String toString()

Return a handy string representation for debugging purposes. Not for machine consumption.

Overrides:

toString in class Object

isFrozen

public boolean isFrozen()

Answer true iff this node is "frozen", ie its value is fixed, when it is encountered; that is, it is not a Bind or JustBound node.

finder

public Node finder(Domain d)

Answer a Node value to use when this QueryValue is used to select objects in a Graph::find() operation; for concrete nodes, that very node, for variables their current value (ANY if not bound).

mustMatch

public boolean mustMatch()

Answer true iff this QueryNode must be used in a triple-match of its owning QueryTriple.

match

public boolean match(Domain d,
                     Node x)

Answer true iff this QueryNode matches, in the context of the binding Domain d, the node x.

matchOrBind

public abstract boolean matchOrBind(Domain d,
                                    Node x)

Optimisation: the action to be performed when matching a just-bound variable or binding a newly-bound variable, or nothing for any other kind of QueryNode.

classify

public static QueryNode classify(QueryNodeFactory f,
                                 Mapping map,
                                 Set<Node> recent,
                                 Node n)

Answer a QueryNode that classifies the argument node n. The factory f is used to create the different QueryNodes, allowing different classifiers to use their own subclasses of QueryNode if they wish. map is the variable-to-index map, and recent is the set of those variables "just" bound, ie, earlier in the same triple.