uk.ac.gla.terrier.structures
Class DocumentIndex

java.lang.Object
  uk.ac.gla.terrier.structures.DocumentIndex

All Implemented Interfaces:

Closeable, IndexConfigurable

Direct Known Subclasses:

DocumentIndexEncoded, DocumentIndexInMemory

public class DocumentIndex
extends java.lang.Object
implements Closeable, IndexConfigurable

This class provides an interface for accessing the document index file. Each entry in the document index consists of a document id, the document number, and the length of the document, that is the number of terms that make up the document.

Version:

$Revision: 1.47 $

Author:

Gianni Amati, Vassilis Plachouras

Field Summary

int	entryLength The length in bytes of an entry in the file.

Constructor Summary

DocumentIndex()
A default constructor for the class.

DocumentIndex(java.lang.String filename)
A constructor of a document index from a given filename.

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

Method Summary

void	close() Closes the random access file.
FilePosition	getDirectIndexEndOffset() Returns the ending offset of the document's entry in the direct index.
FilePosition	getDirectIndexStartOffset() Returns the starting offset of the document's entry in the direct index.
int	getDocumentId(java.lang.String docno) Returns the document's id for the given docno.
int	getDocumentLength(int i) Reading the length for the i-th document.
int	getDocumentLength(java.lang.String docno) Return the length of the document with the given docno.
java.lang.String	getDocumentNumber(int i) Reading the docno for the i-th document.
int	getNumberOfDocuments() Returns the number of documents in the collection.
static void	main(java.lang.String[] args)
void	print() Prints out to the standard error stream the contents of the document index file.
boolean	seek(int i) Seeks from the document index the i-th entry.
boolean	seek(java.lang.String docno) Seeks the document index entry for the given document number.
void	setDocnoEntryLength(int l) Set the length of docnos in the index file
void	setIndex(Index i) This structure can be configured by the Index object.

Methods inherited from class java.lang.Object

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

Field Detail

entryLength

public int entryLength

The length in bytes of an entry in the file. It is 2*sizeof(int) plus the length of the stored document number plus sizeof(long) plus sizeof(byte).

Constructor Detail

DocumentIndex

public DocumentIndex()

A default constructor for the class.

DocumentIndex

public DocumentIndex(java.lang.String filename)

A constructor of a document index from a given filename.
For the document pointers file we replace the extension of the document index file with the right default extension.
The given name should have an extension.

Parameters:

filename - String the filename of the document index, with an extension

DocumentIndex

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

Method Detail

setIndex

public void setIndex(Index i)

This structure can be configured by the Index object. In particular, the length docno.byte.length can be picked up automatically from the index for non-default installations.

Specified by:

setIndex in interface IndexConfigurable

Parameters:

i - Index object to use

setDocnoEntryLength

public void setDocnoEntryLength(int l)

Set the length of docnos in the index file

close

public void close()

Closes the random access file.

Specified by:

close in interface Closeable

print

public void print()

Prints out to the standard error stream the contents of the document index file.

getDocumentId

public int getDocumentId(java.lang.String docno)

Returns the document's id for the given docno.

Parameters:

docno - java.lang.String The document's number

Returns:

int The document's id, or -1 if docno was not found in the index.

getDocumentLength

public int getDocumentLength(int i)

Reading the length for the i-th document.

Parameters:

i - the index of the document.

Returns:

the length of the i-th document, or -1 if the docid i wasn't found in the index.

getDocumentLength

public int getDocumentLength(java.lang.String docno)

Return the length of the document with the given docno. Creation date: (29/05/2003 10:56:49)

Parameters:

docno - java.lang.String The document's number

Returns:

int The document's length, or -1 if the docno wasn't found in the index.

getDocumentNumber

public java.lang.String getDocumentNumber(int i)

Reading the docno for the i-th document.

Parameters:

i - the index of the document.

Returns:

the document number of the i-th document, or null if the docid i wasn't found in the index.

getDirectIndexEndOffset

public FilePosition getDirectIndexEndOffset()

Returns the ending offset of the document's entry in the direct index.

Returns:

FilePosition an offset in the direct index.

getNumberOfDocuments

public int getNumberOfDocuments()

Returns the number of documents in the collection.

Returns:

the number of documents in the collection.

getDirectIndexStartOffset

public FilePosition getDirectIndexStartOffset()

Returns the starting offset of the document's entry in the direct index.

Returns:

FilePosition an offset in the direct index.

seek

public boolean seek(int i)
             throws java.io.IOException

Seeks from the document index the i-th entry.

Parameters:

i - the document id.

Returns:

boolean true if it was found, otherwise it returns false.

Throws:

java.io.IOException

seek

public boolean seek(java.lang.String docno)
             throws java.io.IOException

Seeks the document index entry for the given document number.

Parameters:

docno - java.lang.String the document's number

Returns:

true if the document was found, false otherwise.

Throws:

java.io.IOException - an input/output exception when it can not read from the file

main

public static void main(java.lang.String[] args)