pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / src / java / org / apache / lucene / search / PhraseScorer.java

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/search/PhraseScorer.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/search/PhraseScorer.java
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+package org.apache.lucene.search;
+
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import java.io.IOException;
+
+/** Expert: Scoring functionality for phrase queries.
+ * <br>A document is considered matching if it contains the phrase-query terms  
+ * at "valid" positions. What "valid positions" are
+ * depends on the type of the phrase query: for an exact phrase query terms are required 
+ * to appear in adjacent locations, while for a sloppy phrase query some distance between 
+ * the terms is allowed. The abstract method {@link #phraseFreq()} of extending classes
+ * is invoked for each document containing all the phrase query terms, in order to 
+ * compute the frequency of the phrase query in that document. A non zero frequency
+ * means a match. 
+ */
+abstract class PhraseScorer extends Scorer {
+  protected byte[] norms;
+  protected float value;
+
+  PhrasePositions min, max;
+
+  private float freq; //phrase frequency in current doc as computed by phraseFreq().
+
+  PhraseScorer(Weight weight, PhraseQuery.PostingsAndFreq[] postings,
+      Similarity similarity, byte[] norms) {
+    super(similarity, weight);
+    this.norms = norms;
+    this.value = weight.getValue();
+
+    // convert tps to a list of phrase positions.
+    // note: phrase-position differs from term-position in that its position
+    // reflects the phrase offset: pp.pos = tp.pos - offset.
+    // this allows to easily identify a matching (exact) phrase 
+    // when all PhrasePositions have exactly the same position.
+    if (postings.length > 0) {
+      min = new PhrasePositions(postings[0].postings, postings[0].position, 0);
+      max = min;
+      max.doc = -1;
+      for (int i = 1; i < postings.length; i++) {
+        PhrasePositions pp = new PhrasePositions(postings[i].postings, postings[i].position, i);
+        max.next = pp;
+        max = pp;
+        max.doc = -1;
+      }
+      max.next = min; // make it cyclic for easier manipulation
+    }
+  }
+
+  @Override
+  public int docID() {
+    return max.doc; 
+  }
+
+  @Override
+  public int nextDoc() throws IOException {
+    return advance(max.doc);
+  }
+
+  private boolean advanceMin(int target) throws IOException {
+    if (!min.skipTo(target)) { 
+      max.doc = NO_MORE_DOCS; // for further calls to docID() 
+      return false;
+    }
+    min = min.next; // cyclic
+    max = max.next; // cyclic
+    return true;
+  }
+
+  @Override
+  public float score() throws IOException {
+    //System.out.println("scoring " + max.doc);
+    float raw = getSimilarity().tf(freq) * value; // raw score
+    return norms == null ? raw : raw * getSimilarity().decodeNormValue(norms[max.doc]); // normalize
+  }
+
+  @Override
+  public int advance(int target) throws IOException {
+    freq = 0.0f;
+    if (!advanceMin(target)) {
+      return NO_MORE_DOCS;
+    }        
+    boolean restart=false;
+    while (freq == 0.0f) {
+      while (min.doc < max.doc || restart) {
+        restart = false;
+        if (!advanceMin(max.doc)) {
+          return NO_MORE_DOCS;
+        }        
+      }
+      // found a doc with all of the terms
+      freq = phraseFreq(); // check for phrase
+      restart = true;
+    } 
+
+    // found a match
+    return max.doc;
+  }
+  
+  /**
+   * phrase frequency in current doc as computed by phraseFreq().
+   */
+  @Override
+  public final float freq() {
+    return freq;
+  }
+
+  /**
+   * For a document containing all the phrase query terms, compute the
+   * frequency of the phrase in that document. 
+   * A non zero frequency means a match.
+   * <br>Note, that containing all phrase terms does not guarantee a match - they have to be found in matching locations.  
+   * @return frequency of the phrase in current doc, 0 if not found. 
+   */
+  abstract float phraseFreq() throws IOException;
+
+  @Override
+  public String toString() { return "scorer(" + weight + ")"; }
+ 
+}