Package it.unimi.di.big.mg4j.index

Interface IndexReader

All Superinterfaces:

AutoCloseable, Closeable, SafelyCloseable

All Known Implementing Classes:

AbstractIndexClusterIndexReader, AbstractIndexReader, BitStreamHPIndexReader, BitStreamIndexReader, DocumentalClusterIndexReader, GammaDeltaGammaDeltaBitStreamHPIndexReader, GammaDeltaGammaDeltaBitStreamIndexReader, LexicalClusterIndexReader, QuasiSuccinctIndexReader, SkipGammaDeltaGammaDeltaBitStreamIndexReader

public interface IndexReader
extends SafelyCloseable

Provides access to an inverted index.

An Index contains global read-only metadata. To get actual data from an index, you need to get an index reader via a call to Index.getReader(). Once you have an index reader, you can ask for the documents matching a term.

Alternatively, you can perform a read-once scan of the index calling nextIterator(), which will return in order the index iterators of all terms of the underlying index. More generally, nextIterator() returns an iterator positioned at the start of the inverted list of the term after the current one. When called just after the reader creation, it returns an index iterator for the first term.

Warning: An index reader is exactly what it looks like—a reader. It cannot be used by many threads at the same time, and all its access methods are exclusive: if you obtain a document iterator, the previous one is no longer valid. However, you can generate many readers, and use them concurrently.

Warning: Invoking the DocumentIterator.dispose() method on iterators returned by an instance of this class will invoke Closeable.close() on the instance, thus making the instance no longer accessible. This behaviour is necessary to handle cases in which a reader is created on-the-fly just to create an iterator.

Since:

1.0

Author:

Paolo Boldi, Sebastiano Vigna

Method Summary

Modifier and Type	Method	Description
IndexIterator	documents(long termNumber)	Returns a document iterator over the documents containing a term.
IndexIterator	documents(CharSequence term)	Returns an index iterator over the documents containing a term; the term is given explicitly.
IndexIterator	nextIterator()	Returns an IndexIterator on the term after the current one (optional operation).

Methods inherited from interface java.io.Closeable

close

Method Detail

documents

IndexIterator documents(long termNumber)
                 throws IOException

Returns a document iterator over the documents containing a term.

Note that the index iterator returned by this method will return null on a call to term().

Note that it is always possible to call this method with argument 0, even if the underlying index does not provide random access.

Parameters:

termNumber - the number of a term.

Throws:

UnsupportedOperationException - if this index reader is not accessible by term number.

IOException

documents

IndexIterator documents(CharSequence term)
                 throws IOException

Returns an index iterator over the documents containing a term; the term is given explicitly.

Unless the term processor of the associated index is null, words coming from a query will have to be processed before being used with this method.

Note that the index iterator returned by this method will return term on a call to term().

Parameters:

term - a term (the term will be downcased if the index is case insensitive).

Throws:

UnsupportedOperationException - if the term map is not available for the underlying index.

IOException

nextIterator

IndexIterator nextIterator()
                    throws IOException

Returns an IndexIterator on the term after the current one (optional operation).

Note that after creation there is no current term. Thus, the first call to this method will return an IndexIterator on the first term. As a consequence, repeated calls to this method provide a way to scan sequentially an index.

Returns:

the index iterator of the next term, or null if there are no more terms after the current one.

Throws:

IOException