Source Code Cross Referenced for PromotionOffer.java in  » XML » saxonb » net » sf » saxon » expr » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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Java Source Code / Java Documentation » XML » saxonb » net.sf.saxon.expr 
Source Cross Referenced  Class Diagram Java Document (Java Doc) 


001:        package net.sf.saxon.expr;
002:
003:        import net.sf.saxon.sort.DocumentSorter;
004:        import net.sf.saxon.sort.Reverser;
005:        import net.sf.saxon.trans.XPathException;
006:        import net.sf.saxon.value.SequenceType;
007:        import net.sf.saxon.functions.Current;
008:        import net.sf.saxon.type.TypeHierarchy;
009:
010:        /**
011:         * PromotionOffer is an object used transiently during compilation of an expression. It contains
012:         * information passed by a containing expression to its subexpressions, when looking for subexpressions
013:         * that can be promoted to a higher level because they are not dependent on the context established
014:         * by the containing expression. The object is also used to pass back return information when the
015:         * promotion actually takes place.
016:         */
017:
018:        public class PromotionOffer {
019:
020:            /**
021:             * FOCUS_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on the
022:             * focus. This is typically used to extract subexpressions from a filter predicate. The offer is
023:             * optional - each subexpression can decide whether it's worth the trouble of promoting itself.
024:             * The offer is normally passed on to subexpressions, except subexpressions that are evaluated
025:             * with a different focus
026:             */
027:
028:            public static final int FOCUS_INDEPENDENT = 10;
029:
030:            /**
031:             * RANGE_INDEPENDENT requests promotion of all non-trivial subexpressions that don't depend on a
032:             * specified range variable. This is typically used to extract subexpressions from the action of
033:             * a for expression or the condition of a some/every quantified expression. The offer is
034:             * optional - each subexpression can decide whether it's worth the trouble of promoting itself.
035:             * The offer is normally passed on to subexpressions, except subexpressions that are evaluated
036:             * with a different focus or a different range variable, because these may have other dependencies
037:             * that prevent their promotion.
038:             */
039:
040:            public static final int RANGE_INDEPENDENT = 11;
041:
042:            /**
043:             * Inline variable references causes all references to a variable V to be replaced by the
044:             * expression E. The variable is supplied in the "binding" property; the replacement expression
045:             * in the containingExpression property. A special case is where the replacement expression is
046:             * a ContextItemExpression; in this case the offer is not passed on to subexpressions where
047:             * the context is different.
048:             */
049:
050:            public static final int INLINE_VARIABLE_REFERENCES = 12;
051:
052:            // Note: After inlining variable references, it is possible for an expression to appear at more
053:            // than one place in the expression tree. This seems dangerous, since a rewrite applied to one
054:            // branch might be inappropriate in another branch. We get away with it because the only expressions
055:            // that we are inline are very simple ones: (a) a ContextItemExpression, and (b) another VariableReference.
056:
057:            /**
058:             * UNORDERED indicates that the containing expression does not require the results
059:             * to be delivered in any particular order. The boolean mustEliminateDuplicates
060:             * is set if duplicate items in the result are not allowed.
061:             */
062:
063:            public static final int UNORDERED = 13;
064:
065:            /**
066:             * REPLACE_CURRENT causes calls to the XSLT current() function to be replaced by
067:             * reference to a variable. The variable binding is the single member of the array bindingList
068:             */
069:
070:            public static final int REPLACE_CURRENT = 14;
071:
072:            /**
073:             * The optimizer in use
074:             */
075:
076:            private Optimizer optimizer;
077:
078:            /**
079:             * action is one of the possible promotion actions, FOCUS_INDEPENDENT, RANGE_INDEPENDENT,
080:             * INLINE_VARIABLE_REFERENCES, ANY_ORDER, ANY_ORDER_UNIQUE
081:             */
082:
083:            public int action;
084:
085:            /**
086:             * In the case of FOCUS_INDEPENDENT, "promoteDocumentDependent" is a boolean that, when set to
087:             * true, indicates that it is safe to promote a subexpression that depends on the context document
088:             * but not on other aspects of the focus. This is the case, for example, in a filter expression when
089:             * it is known that all the nodes selected by the expression will be in the same document - as happens
090:             * when the filter is applied to a path expression. This allows subexpressions such as key() to be
091:             * promoted
092:             */
093:
094:            public boolean promoteDocumentDependent = false;
095:
096:            /**
097:             * In the case of FOCUS_INDEPENDENT, "promoteXSLTFunctions" is a boolean that, when set to true, indicates
098:             * that it is safe to promote XSLT functions such as current(). This flag is set when rewriting XPath expressions
099:             * and is unset when rewriting XSLT templates.
100:             */
101:
102:            public boolean promoteXSLTFunctions = true;
103:
104:            /**
105:             * In the case of UNORDERED, "mustEliminateDuplicates" is a boolean that is set to
106:             * true if the nodes can be delivered in any order so long as there are no duplicates
107:             * (for example, as required by the count() function). If this boolean is false, the
108:             * nodes can be delivered in any order and duplicates are allowed (for example, as
109:             * required by the boolean() function).
110:             */
111:
112:            public boolean mustEliminateDuplicates = true;
113:
114:            /**
115:             * In the case of RANGE_INDEPENDENT and WHERE_CLAUSE, "binding" identifies the range variables whose dependencies
116:             * we are looking for. For INLINE_VARIABLE_REFERENCES it is a single Binding that we are aiming to inline
117:             */
118:
119:            public Binding[] bindingList;
120:
121:            /**
122:             * When a promotion offer is made, containingExpression identifies the level to which the promotion
123:             * should occur. When a subexpression is promoted, an expression of the form let $VAR := SUB return ORIG
124:             * is created, and this replaces the original containingExpression within the PromotionOffer.
125:             */
126:
127:            public Expression containingExpression;
128:
129:            /**
130:             * Flag that is set if the offer has been accepted, that is, if the expression has changed
131:             */
132:
133:            public boolean accepted = false;
134:
135:            /**
136:             * Create a PromotionOffer for use with a particular Optimizer
137:             */
138:
139:            public PromotionOffer(Optimizer optimizer) {
140:                this .optimizer = optimizer;
141:            }
142:
143:            /**
144:             * Get the optimizer in use
145:             */
146:
147:            public Optimizer getOptimizer() {
148:                return optimizer;
149:            }
150:
151:            /**
152:             * Method to test whether a subexpression qualifies for promotion, and if so, to
153:             * accept the promotion.
154:             * @return if promotion was done, returns the expression that should be used in place
155:             * of the child expression. If no promotion was done, returns null.
156:             */
157:
158:            public Expression accept(Expression child) throws XPathException {
159:                switch (action) {
160:                case RANGE_INDEPENDENT: {
161:                    int properties = child.getSpecialProperties();
162:                    if (((properties & StaticProperty.NON_CREATIVE) != 0)
163:                            && !ExpressionTool.dependsOnVariable(child,
164:                                    bindingList)) {
165:                        return promote(child);
166:                    }
167:                    break;
168:                }
169:
170:                case FOCUS_INDEPENDENT: {
171:                    int dependencies = child.getDependencies();
172:                    int properties = child.getSpecialProperties();
173:                    if (!promoteXSLTFunctions
174:                            && ((dependencies & StaticProperty.DEPENDS_ON_XSLT_CONTEXT) != 0)) {
175:                        break;
176:                    }
177:                    if ((dependencies & StaticProperty.DEPENDS_ON_FOCUS) == 0
178:                            && (properties & StaticProperty.NON_CREATIVE) != 0) {
179:                        return promote(child);
180:                    } else if (promoteDocumentDependent
181:                            && (dependencies & StaticProperty.DEPENDS_ON_NON_DOCUMENT_FOCUS) == 0
182:                            && (properties & StaticProperty.NON_CREATIVE) != 0) {
183:                        return promote(child);
184:                    }
185:                    break;
186:                }
187:
188:                case REPLACE_CURRENT: {
189:                    if (child instanceof  Current) {
190:                        VariableReference var = new VariableReference(
191:                                ((Assignation) containingExpression)
192:                                        .getVariableDeclaration());
193:                        var.setParentExpression(child.getParentExpression());
194:                        return var;
195:                    }
196:                    break;
197:                }
198:
199:                case INLINE_VARIABLE_REFERENCES: {
200:                    if (child instanceof  VariableReference
201:                            && ((VariableReference) child).getBinding() == bindingList[0]) {
202:                        return containingExpression;
203:                    }
204:                    break;
205:                }
206:                case UNORDERED: {
207:                    if (child instanceof  Reverser) {
208:                        return ((Reverser) child).getBaseExpression();
209:                    } else if (child instanceof  DocumentSorter
210:                            && !mustEliminateDuplicates) {
211:                        return ((DocumentSorter) child).getBaseExpression();
212:                    }
213:                    break;
214:                }
215:                default:
216:                    throw new UnsupportedOperationException(
217:                            "Unknown promotion action " + action);
218:                }
219:                return null;
220:            }
221:
222:            /**
223:             * Method to do the promotion.
224:             */
225:
226:            private Expression promote(Expression child) {
227:                final RangeVariableDeclaration decl = new RangeVariableDeclaration();
228:                decl.setVariableName("zz:" + decl.hashCode());
229:                final TypeHierarchy th = optimizer.getConfiguration()
230:                        .getNamePool().getTypeHierarchy();
231:                SequenceType type = SequenceType.makeSequenceType(child
232:                        .getItemType(th), child.getCardinality());
233:                decl.setRequiredType(type);
234:
235:                VariableReference var = new VariableReference(decl);
236:                ExpressionTool.copyLocationInfo(containingExpression, var);
237:                var.setParentExpression(child.getParentExpression());
238:
239:                Container container = containingExpression
240:                        .getParentExpression();
241:                LetExpression let = new LetExpression();
242:                let.setVariableDeclaration(decl);
243:                let.setSequence(LazyExpression.makeLazyExpression(child));
244:                let.setAction(containingExpression);
245:                let.setParentExpression(container);
246:                let.adoptChildExpression(containingExpression);
247:                containingExpression = let;
248:                accepted = true;
249:
250:                return var;
251:            }
252:
253:        }
254:
255:        //
256:        // The contents of this file are subject to the Mozilla Public License Version 1.0 (the "License");
257:        // you may not use this file except in compliance with the License. You may obtain a copy of the
258:        // License at http://www.mozilla.org/MPL/
259:        //
260:        // Software distributed under the License is distributed on an "AS IS" basis,
261:        // WITHOUT WARRANTY OF ANY KIND, either express or implied.
262:        // See the License for the specific language governing rights and limitations under the License.
263:        //
264:        // The Original Code is: all this file.
265:        //
266:        // The Initial Developer of the Original Code is Michael H. Kay
267:        //
268:        // Portions created by (your name) are Copyright (C) (your legal entity). All Rights Reserved.
269:        //
270:        // Contributor(s): none.
271:        //
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