ivory.core.data.index

Interface PostingsList

All Superinterfaces:

Writable

All Known Implementing Classes:

PostingsListDocSortedNonPositional, PostingsListDocSortedPositional, PostingsListDocSortedPositionalPForDelta

public interface PostingsList
extends Writable

Interface representing a postings list, which contains a list of individual postings. The ordering of the postings depends on the concrete implementation. Postings lists may or may not store positional information.

Note that there are subtle but important differences between:

• size(), which returns the number of postings that have been added to this list (i.e., intermediate state).
• getNumberOfPostings() and setNumberOfPostings(int), which return and set the number of postings that will ultimately be added to this list (i.e., final state). For many encoding schemes, this is required to be known in advance (i.e., before any postings are added to the list).
• getDf(), which returns the document frequency of the term associated with this postings list. In a large collection with many document partition, this returns the global document frequency (whereas the previous two methods deal with this specific partition). In a collection with only a single partition, this is exactly the same value as getNumberOfPostings()

Author:

Jimmy Lin

Method Summary

Methods

Modifier and Type	Method and Description
void	add(int docno, short score, TermPositions pos) Adds a posting to this postings list.
void	clear() Clears this postings list.
long	getCf() Returns the collection frequency of the term associated with this postings list.
int	getCollectionDocumentCount() Returns the number of documents in this collection.
int	getDf() Returns the document frequency of the term associated with this postings list.
int	getNumberOfPostings() Returns the number of postings that will be added to this list.
PostingsReader	getPostingsReader() Returns the PostingsReader associated with this postings list.
byte[]	getRawBytes() Returns the raw byte array representation of this postings list.
byte[]	serialize()
void	setCf(long cf)
void	setCollectionDocumentCount(int docs) Sets the number of documents in this collection.
void	setDf(int df)
void	setNumberOfPostings(int n) Sets the number of postings that will be added to this list.
int	size() Returns the number of postings that have been added to this postings list.

Methods inherited from interface org.apache.hadoop.io.Writable

readFields, write

Method Detail

add

void add(int docno,
       short score,
       TermPositions pos)

Adds a posting to this postings list.

Parameters:

docno - docno of the posting

score - score of the posting

pos - positional information (optional)

clear

void clear()

Clears this postings list.

getCf

long getCf()

Returns the collection frequency of the term associated with this postings list. This method is not meaningful for impact-sorted indexes.

getCollectionDocumentCount

int getCollectionDocumentCount()

Returns the number of documents in this collection.

getDf

int getDf()

Returns the document frequency of the term associated with this postings list. Note this is may be different from getNumberOfPostings() because of document partitioning for large collections. In these cases, this method should return the global document frequency, whereas getNumberOfPostings() should return the document frequency in this partition. In a collection with only a single partition, this is exactly the same value as getNumberOfPostings(). This method is not meaningful for impact-sorted indexes.

getNumberOfPostings

int getNumberOfPostings()

Returns the number of postings that will be added to this list. That is, this method returns the value set by setNumberOfPostings(int). Note that under most circumstances this method will return a different value than size(), which returns the number of postings that have already been added.

getPostingsReader

PostingsReader getPostingsReader()

Returns the PostingsReader associated with this postings list.

getRawBytes

byte[] getRawBytes()

Returns the raw byte array representation of this postings list.

serialize

byte[] serialize()
                 throws IOException

Throws:

IOException

setCf

void setCf(long cf)

setCollectionDocumentCount

void setCollectionDocumentCount(int docs)

Sets the number of documents in this collection. This value is necessary for certain encoding schemes (e.g., Golomb encoding). This method is typically called before postings are adding to the postings list.

setDf

void setDf(int df)

setNumberOfPostings

void setNumberOfPostings(int n)

Sets the number of postings that will be added to this list. For certain encoding schemes (e.g., Golomb encoding), this value is required before any postings are added.

size

int size()

Returns the number of postings that have been added to this postings list. Note that under most circumstances this method will return a different value than getNumberOfPostings(), which returns the number of postings that will eventually be added (required for certain encoding schemes).