bindingvector.java

jena2.5.4推理机系统的一种最基本实现 HP实验室出品

        StringBuffer buffer = new StringBuffer();
        for (int i = 0; i < environment.length; i++) {
            if (environment[i] == null) {
                buffer.append("-");
            } else {
                buffer.append(PrintUtil.print(environment[i]));
            }
            buffer.append(" ");
        }
        return buffer.toString();
    }
        
    /**
     * Unify a goal with the head of a rule. This is a poor-man's unification,
     * we should try swtiching to a more conventional global-variables-with-trail
     * implementation in the future.
     * @param goal the goal pattern which it being matched to a rule
     * @param head the head pattern of the rule which is being instantiated
     * @param numRuleVars the length of the environment to allocate.
     * @return An initialized binding environment for the rule variables
     * or null if the unification fails. If a variable in the environment becomes
     * aliased to another variable through the unification this is represented
     * by having its value in the environment be the variable to which it is aliased.
     */ 
    public static BindingVector unify(TriplePattern goal, TriplePattern head, int numRuleVars) {
        Node[] gEnv = new Node[numRuleVars];       // TODO: check
        Node[] hEnv = new Node[numRuleVars];
        
        if (!unify(goal.getSubject(), head.getSubject(), gEnv, hEnv)) {
            return null;
        } 
        if (!unify(goal.getPredicate(), head.getPredicate(), gEnv, hEnv)) {
            return null; 
        } 
        
        Node gObj = goal.getObject();
        Node hObj = head.getObject();
        if (Functor.isFunctor(gObj)) {
            Functor gFunctor = (Functor)gObj.getLiteralValue();
            if (Functor.isFunctor(hObj)) {
                Functor hFunctor = (Functor)hObj.getLiteralValue();
                if ( ! gFunctor.getName().equals(hFunctor.getName()) ) {
                    return null;
                }
                Node[] gArgs = gFunctor.getArgs();
                Node[] hArgs = hFunctor.getArgs();
                if ( gArgs.length != hArgs.length ) return null;
                for (int i = 0; i < gArgs.length; i++) {
                    if (! unify(gArgs[i], hArgs[i], gEnv, hEnv) ) {
                        return null;
                    }
                }
            } else if (hObj instanceof Node_RuleVariable) {
                // temp debug ...
                // Check the goal functor is fully ground
                if (gFunctor.isGround(new BindingVector(gEnv))) {
                    if (!unify(gObj, hObj, gEnv, hEnv)) return null;
                }
                // ... end debug
            } else {
                // unifying simple ground object with functor, failure
                return null;
            }
        } else {
            if (!unify(gObj, hObj, gEnv, hEnv)) return null;
        } 
        // Successful bind if we get here
        return new BindingVector(hEnv);
    }
    
    /**
     * Unify a single pair of goal/head nodes. Unification of a head var to
     * a goal var is recorded using an Integer in the head env to point to a
     * goal env and storing the head var in the goal env slot.
     * @return true if they are unifiable, side effects the environments
     */
    private static boolean unify(Node gNode, Node hNode, Node[] gEnv, Node[] hEnv) {
        if (hNode instanceof Node_RuleVariable) {
            int hIndex = ((Node_RuleVariable)hNode).getIndex();
            if (gNode instanceof Node_RuleVariable) {
                // Record variable bind between head and goal to detect aliases
                int gIndex = ((Node_RuleVariable)gNode).getIndex();
                if (gIndex < 0) return true;
                if (gEnv[gIndex] == null) {
                    // First time bind so record link 
                    gEnv[gIndex] = hNode;
                } else {
                    // aliased var so follow trail to alias
                    // but ignore self-aliases
                    Node gVal = gEnv[gIndex];
                    if (hIndex != gIndex || ! (gVal instanceof Node_RuleVariable)) {
                        hEnv[hIndex] = gVal;
                    }
                }
            } else {
                Node hVal = hEnv[hIndex];
                if (hVal == null) {
                    hEnv[hIndex] = gNode;
                } else {
                    // Already bound
                    if (hVal instanceof Node_RuleVariable) {
                        // Already an aliased variable, so bind both this an the alias
                        hEnv[((Node_RuleVariable)hVal).getIndex()] = gNode;
                        hEnv[hIndex] = gNode;
                    } else {
                        // Already bound to a ground node
                        return hVal.sameValueAs(gNode); 
                    }
                }
            }
            return true;
        } else {
            if (gNode instanceof Node_RuleVariable) {
                int gIndex = ((Node_RuleVariable)gNode).getIndex();
                if (gIndex < 0) return true;
                Node gVal = gEnv[gIndex]; 
                if (gVal == null) {
                    //. No variable alias so just record binding
                    gEnv[gIndex] = hNode;
                } else if (gVal instanceof Node_RuleVariable) {
                    // Already an alias
                    hEnv[((Node_RuleVariable)gVal).getIndex()] = hNode;
                    gEnv[gIndex] = hNode;
                } else {
                    return gVal.sameValueAs(hNode);
                }
                return true;
            } else {
                return hNode.sameValueAs(gNode); 
            }
        }
    }
  
    /** Equality override */
    public boolean equals(Object o) {
        // Pass 1 - just check basic shape
        if (! (o instanceof BindingVector) ) return false;
        Node[] other = ((BindingVector)o).environment;
        if (environment.length != other.length) return false;
        for (int i = 0; i < environment.length; i++) {
            Node n = environment[i];
            Node no = other[i];
            if (n == null) {
                if (no != null) return false;
            } else {
                if (! n.sameValueAs(no)) return false;
            }
        }
        return true;
    }
        
    /** hash function override */
    public int hashCode() {
        int hash = 0;
        for (int i = 0; i < environment.length; i++) {
            Node n = environment[i];
            hash = (hash << 1) ^ (n == null ? 0x537c: n.hashCode());
        }
        return hash;
    }
    

}



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