uk.ac.gla.terrier.structures.indexing
Class BlockInvertedIndexBuilder

java.lang.Object
  uk.ac.gla.terrier.structures.indexing.InvertedIndexBuilder
      uk.ac.gla.terrier.structures.indexing.BlockInvertedIndexBuilder

Direct Known Subclasses:

UTFBlockInvertedIndexBuilder

public class BlockInvertedIndexBuilder
extends InvertedIndexBuilder

Builds an inverted index saving term-block information. It optionally saves term-field information as well.

Algorithm:

1. While there are terms left:
   1. Read M term ids from lexicon, in lexicographical order
   2. Read the occurrences of these M terms into memory from the direct file
   3. Write the occurrences of these M terms to the inverted file
2. Rewrite the lexicon, removing block frequencies, and adding inverted file offsets
3. Write the collection statistics

Lexicon term selection: There are two strategies of selecting the number of terms to read from the lexicon. The trade-off here is to read a small enough number of terms into memory such that the occurrences of all those terms from the direct file can fit in memory. On the other hand, the less terms that are read implies more iterations, which is I/O expensive, as the entire direct file has to be read for every iteration.
The two strategies are:

• Read a fixed number of terms on each iterations - this corresponds to the property invertedfile.processterms
• Read a fixed number of occurrences (pointers) on each iteration. The number of pointers can be determined using the sum of frequencies of each term from the lexicon. This corresponds to the property invertedfile.processpointers.

By default, the 2nd strategy is chosen, unless the invertedfile.processpointers has a zero value specified.

Properties:

• invertedfile.processterms - the number of terms to process in each iteration. Defaults to 25,000
• invertedfile.processpointers - the number of pointers to process in each iteration. Defaults to 2,000,000, which specifies that invertedfile.processterms should be read from the lexicon, regardless of the number of pointers.

Version:

$Revision: 1.40 $

Author:

Douglas Johnson & Vassilis Plachouras & Craig Macdonald

Field Summary

Fields inherited from class uk.ac.gla.terrier.structures.indexing.InvertedIndexBuilder

numberOfDocuments, numberOfPointers, numberOfTokens, numberOfUniqueTerms

Constructor Summary

BlockInvertedIndexBuilder()
Deprecated.

BlockInvertedIndexBuilder(Index index)

BlockInvertedIndexBuilder(java.lang.String filename)
Deprecated. use this() or this(String, String) instead

BlockInvertedIndexBuilder(java.lang.String path, java.lang.String prefix)
Deprecated.

Method Summary

void	createInvertedIndex() This method creates the block html inverted index.

Methods inherited from class uk.ac.gla.terrier.structures.indexing.InvertedIndexBuilder

close, displayMemoryUsage, getLexInputStream, getLexOutputStream

Methods inherited from class java.lang.Object

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

Constructor Detail

BlockInvertedIndexBuilder

public BlockInvertedIndexBuilder()

Deprecated.

Creates an instance of the BlockInvertedIndex class.

BlockInvertedIndexBuilder

public BlockInvertedIndexBuilder(java.lang.String filename)

Deprecated. use this() or this(String, String) instead

Creates an instance of the BlockInvertedIndex class using the given filename.

Parameters:

filename - the name of the inverted file

BlockInvertedIndexBuilder

public BlockInvertedIndexBuilder(java.lang.String path,
                                 java.lang.String prefix)

Deprecated.

BlockInvertedIndexBuilder

public BlockInvertedIndexBuilder(Index index)

Method Detail

createInvertedIndex

public void createInvertedIndex()

This method creates the block html inverted index. The approach used is described briefly: for a group of M terms from the lexicon we build the inverted file and save it on disk. In this way, the number of times we need to read the direct file is related to the parameter M, and consequently to the size of the available memory.

Overrides:

createInvertedIndex in class InvertedIndexBuilder