uk.ac.gla.terrier.structures
Class UTFBlockLexicon

java.lang.Object
  uk.ac.gla.terrier.structures.Lexicon
      uk.ac.gla.terrier.structures.BlockLexicon
          uk.ac.gla.terrier.structures.UTFBlockLexicon

All Implemented Interfaces:

java.lang.Iterable<java.lang.String>, Closeable

public class UTFBlockLexicon
extends BlockLexicon

A lexicon class that saves the number of different blocks a term appears in, using UTF encoding of Strings. It is used only during creating a utf block inverted index. After the utf block inverted index has been created, the utf block lexicon is transformed into a utf lexicon.

Version:

$Revision: 1.16 $

Author:

Douglas Johnson, Vassilis Plachouras

Field Summary

static int

lexiconEntryLength The size in bytes of an entry in the lexicon file.

Constructor Summary

UTFBlockLexicon()
A default constructor.

UTFBlockLexicon(java.lang.String lexiconName)
Constructs an instace of BlockLexicon and opens the corresponding file.

UTFBlockLexicon(java.lang.String path, java.lang.String prefix)

Method Summary

boolean	findTerm(int termId) Finds the term given its term code.
boolean	findTerm(java.lang.String _term) Performs a binary search in the lexicon in order to locate the given term.
int	getBlockFrequency() Returns the block frequency for the given term
static int	numberOfEntries(java.io.File f) returns the number of entries in the lexicon named by f
static int	numberOfEntries(java.lang.String filename) returns the number of entries in the lexicon named by filename
boolean	seekEntry(int i) Seeks the i-th entry of the lexicon.
boolean	updateEntry(int i, int frequency, long endOffset, byte endBitOffset) Deprecated. Block Lexicons are used during indexing, but not during retrieval.

Methods inherited from class uk.ac.gla.terrier.structures.Lexicon

close, getEndBitOffset, getEndOffset, getIthLexiconEntry, getLexiconEntry, getLexiconEntry, getNt, getNumberOfLexiconEntries, getStartBitOffset, getStartOffset, getTerm, getTermId, getTF, iterator, print

Methods inherited from class java.lang.Object

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

Field Detail

lexiconEntryLength

public static final int lexiconEntryLength

The size in bytes of an entry in the lexicon file. An entry corresponds to a string, an int (termCode), an int (docf), an int (tf), a long (the offset of the end of the term's entry in bytes in the inverted file) and a byte (the offset in bits of the last byte of the term's entry in the inverted file.

Constructor Detail

UTFBlockLexicon

public UTFBlockLexicon()

A default constructor.

UTFBlockLexicon

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

UTFBlockLexicon

public UTFBlockLexicon(java.lang.String lexiconName)

Constructs an instace of BlockLexicon and opens the corresponding file.

Parameters:

lexiconName - the name of the lexicon file.

Method Detail

findTerm

public boolean findTerm(int termId)

Finds the term given its term code.

Overrides:

findTerm in class BlockLexicon

Parameters:

termId - the term's id

Returns:

true if the term is found, else return false

findTerm

public boolean findTerm(java.lang.String _term)

Performs a binary search in the lexicon in order to locate the given term. If the term is located, the properties termCharacters, documentFrequency, termFrequency, startOffset, startBitOffset, endOffset and endBitOffset contain the values related to the term.

Overrides:

findTerm in class BlockLexicon

Parameters:

_term - the term to search for.

Returns:

true if the term is found, and false otherwise.

getBlockFrequency

public int getBlockFrequency()

Returns the block frequency for the given term

Overrides:

getBlockFrequency in class BlockLexicon

Returns:

int The block frequency for the given term

seekEntry

public boolean seekEntry(int i)

Seeks the i-th entry of the lexicon.

Overrides:

seekEntry in class BlockLexicon

Parameters:

i - The index of the entry we are looking for.

Returns:

true if the entry was found, false otherwise.

updateEntry

public boolean updateEntry(int i,
                           int frequency,
                           long endOffset,
                           byte endBitOffset)

Deprecated. Block Lexicons are used during indexing, but not during retrieval.

In an already stored entry in the lexicon file, the information about the term frequency, the endOffset in bytes, and the endBitOffset in the last byte, is updated. The term is specified by the index of the entry.

Overrides:

updateEntry in class BlockLexicon

Parameters:

i - the i-th entry

frequency - the term's Frequency

endOffset - the offset of the ending byte in the inverted file

endBitOffset - the offset in bits in the ending byte in the term's entry in inverted file

Returns:

true if the information is updated properly, otherwise return false

numberOfEntries

public static int numberOfEntries(java.io.File f)

returns the number of entries in the lexicon named by f

numberOfEntries

public static int numberOfEntries(java.lang.String filename)

returns the number of entries in the lexicon named by filename