Source Code Cross Referenced for Gateway.java in  » ERP-CRM-Financial » SourceTap-CRM » org » ofbiz » rules » engine » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » ERP CRM Financial » SourceTap CRM » org.ofbiz.rules.engine 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package org.ofbiz.rules.engine;
002:
003:        /**
004:         * <p><b>Title:</b> Gateway
005:         * <p><b>Description:</b> None
006:         * <p>Copyright (c) 1999 Steven J. Metsker.
007:         * <p>Copyright (c) 2001 The Open For Business Project - www.ofbiz.org
008:         *
009:         * <p>Permission is hereby granted, free of charge, to any person obtaining a
010:         *  copy of this software and associated documentation files (the "Software"),
011:         *  to deal in the Software without restriction, including without limitation
012:         *  the rights to use, copy, modify, merge, publish, distribute, sublicense,
013:         *  and/or sell copies of the Software, and to permit persons to whom the
014:         *  Software is furnished to do so, subject to the following conditions:
015:         *
016:         * <p>The above copyright notice and this permission notice shall be included
017:         *  in all copies or substantial portions of the Software.
018:         *
019:         * <p>THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
020:         *  OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
021:         *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
022:         *  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
023:         *  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT
024:         *  OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
025:         *  THE USE OR OTHER DEALINGS IN THE SOFTWARE.
026:         *
027:         * <br>
028:         * <p>A Gateway is a structure that can prove its truth at most
029:         * once before failing.
030:         * <p>
031:         * Examples of gateways are comparisons, negations, and
032:         * mathematical evaluations. For example, <code>Age >
033:         * 18</code> is either true or not, it cannot prove itself in
034:         * more than one way. Also, <code> not married(X)</code> is
035:         * true only if the structure <code>married(X)</code> cannot
036:         * prove itself at all.
037:         * <p>
038:         * The fact that gateways can be true only once is important
039:         * in rules. For example, a rule might contain:
040:         * <blockquote><pre>
041:         *     ..., plays(jim, Game, Rating),
042:         *         Rating >= 7, likes(jane, Game), ...
043:         * </pre></blockquote>
044:         * As this rule proves itself, if it finds a game that Jim
045:         * plays with a rating of, say, 8, the rule will accept that
046:         * <code>Rating >= 7</code>. The rule will then proceed to
047:         * prove the structures after the comparison. The rule may
048:         * succeed with the latter structures many times, but
049:         * eventually these structures will run out of proofs, and the
050:         * rule will fail back to the comparison structure.
051:         * <p>
052:         * On failing back, the rule will ask the comparison for its
053:         * next proof. This amounts to asking if there is a different
054:         * way to prove that 8 is greater than or equal to 7. Since
055:         * the comparison has already succeeded once, which allowed
056:         * the rule to check the latter structures, on failing back
057:         * the comparison will fail. This will cause the rule to fail
058:         * back to the preceding <code>plays</code> structure, which
059:         * may be able to find other proofs.
060:         * <p>
061:         * If a preceding structure succeeds, the rule will move
062:         * forward again, and ask a gateway to prove itself. Since the
063:         * gateway has failed, it will try again to prove itself.
064:         *
065:         * @author Steven J. Metsker
066:         *
067:         * @version 1.0
068:         *
069:         */
070:        public abstract class Gateway extends Structure {
071:
072:            /**
073:             * If this structure is involved in a proof, the gate is
074:             * open and will shut when the rule fails back to this
075:             * structure.
076:             */
077:            protected boolean open = false;
078:
079:            /**
080:             * Allows subclasses to use this form of constructor. This typically
081:             * happens when the subclass object is creating an executable copy
082:             * of itself.
083:             *
084:             * @param   functor   the functor for this gateway
085:             *
086:             * @param   terms   the terms of the gateway
087:             *
088:             * @param   program   the program the gateway will prove itself
089:             *                    against
090:             */
091:            protected Gateway(Object functor, Term[] terms) {
092:                super (functor, terms);
093:            }
094:
095:            /**
096:             * Returns true if the gate is closed and this gateway can find a new
097:             * proof.
098:             * <p>
099:             * A gateway is a structure that can prove itself in at most one
100:             * way. After a successful proof, a gateway leaves its gate open.
101:             * <p>
102:             * If the gate is open when this method executes, this method will
103:             * shut the gate and return false. This occurs after a gateway has
104:             * proven itself true once, and a rule has failed back to the point
105:             * where it is asking the gateway for another proof.
106:             * <p>
107:             * If the gate is not open, this gateway will try to prove itself.
108:             * Then,
109:             * <ul>
110:             * <p><li>
111:             * If the gate is not open and this gateway can prove itself, then
112:             * this method will return true and leave the gate open. Returning
113:             * true allows the containing rule to go on to prove whatever
114:             * structures follow this one. When the rule fails back to this
115:             * gateway, the gate will be open, and at that time this gateway
116:             * will fail.
117:             * <p><li>
118:             * If the gate is not open and this gateway can not prove itself,
119:             * this method returns false.
120:             * </ul>
121:             * <p>
122:             * Upon leaving the gate closed, this method unbinds any variables
123:             * that instantiated as part of this gateway's proof. This method
124:             * also sets rule checking to begin again at the first program rule,
125:             * upon the next request for a proof sent to this gateway.
126:             *
127:             * @param   depth   the depth at which to print tracing information
128:             *
129:             * @return   true   if the gate is closed and this gateway can find a
130:             *                  new proof
131:             */
132:            public boolean canFindNextProof() {
133:                if (open) {
134:                    open = false;
135:                } else {
136:                    open = canProveOnce();
137:                }
138:                if (!open) {
139:                    cleanup();
140:                }
141:                return open;
142:            }
143:
144:            /**
145:             * Returns true if the comparison operator holds true between each
146:             * pair of terms.
147:             * <p>
148:             * This method recovers the comparison operator from the Token which
149:             * is the functor for this Comparison. This method applies this
150:             * comparison to each pair of terms. That is, this method compares
151:             * term 0 with term 1, term 1 with term 2, term 2 with term 3, and
152:             * so on. This method returns true if the comparison holds between
153:             * each adjacent pair of terms.
154:             * <p>
155:             * If a term is a variable, this method uses the term's ground value
156:             * in the comparison.
157:             *
158:             * @param   depth   the depth at which to print trace information
159:             */
160:            public boolean canProveOnce() {
161:                return true;
162:            }
163:
164:            /**
165:             * Insert the method's description here.
166:             * Creation date: (12/7/99 11:09:44 AM)
167:             */
168:            protected void cleanup() {
169:            }
170:        }
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