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Interface DocumentIterator

All Known Subinterfaces:

IndexIterator

All Known Implementing Classes:

AbstractCompositeDocumentIterator, AbstractDocumentIterator, AbstractIndexIterator, AbstractIntersectionDocumentIterator, AbstractIntervalDocumentIterator, AbstractOrderedIntervalDocumentIterator, AbstractUnionDocumentIterator, AlignDocumentIterator, AndDocumentIterator, BitStreamHPIndexReader.BitStreamHPIndexReaderIndexIterator, BitStreamIndexReader.BitStreamIndexReaderIndexIterator, CachingDocumentIterator, ConsecutiveDocumentIterator, DifferenceDocumentIterator, DocumentalConcatenatedClusterDocumentIterator, DocumentalConcatenatedClusterIndexIterator, DocumentalMergedClusterDocumentIterator, DocumentalMergedClusterIndexIterator, FalseDocumentIterator, Index.EmptyIndexIterator, LowPassDocumentIterator, MultiTermIndexIterator, NotDocumentIterator, OrderedAndDocumentIterator, OrDocumentIterator, PayloadPredicateDocumentIterator, QuasiSuccinctIndexReader.AbstractQuasiSuccinctIndexIterator, QuasiSuccinctIndexReader.EliasFanoIndexIterator, QuasiSuccinctIndexReader.RankedIndexIterator, RemappingDocumentIterator, TrueDocumentIterator

public interface DocumentIterator

An iterator over documents (pointers) and their intervals.

Warning: from MG4J 5.0, this class does not implement IntIterator. Moreover, {nextDocument() no longer returns -1 to denote end of iteration, but rather END_OF_LIST.

Each call to nextDocument() will return a document pointer, or END_OF_LIST if no more documents are available. Just after the call to nextDocument(), intervalIterator(Index) will return an interval iterator enumerating intervals in the last returned document for the specified index. The latter method may return, as a special result, a special TRUE value: this means that albeit the current document satisfies the query, there is only a generic empty witness to prove it (see TRUE for some elaboration).

A document iterator is usually structured as composite, with operators as internal nodes and IndexIterators as leaves. The methods accept(DocumentIteratorVisitor) and acceptOnTruePaths(DocumentIteratorVisitor) implement the visitor pattern.

The dispose() method is intended to recursively release all resources associated to a composite document iterator. Note that this is not always what you want, as you might be, say, pooling index readers to reduce the number of file open/close operations. For this reason, we intentionally avoid calling the method “close”.

Warning: interval enumeration can be carried out only just after a call to nextDocument(). Subsequent calls to nextDocument() will reset the internal state of the iterator.

Field Summary

static int

END_OF_LIST A special value denoting that the end of the list has been reached.

Method Summary

<T> T	accept(DocumentIteratorVisitor<T> visitor) Accepts a visitor.
<T> T	acceptOnTruePaths(DocumentIteratorVisitor<T> visitor) Accepts a visitor after a call to nextDocument(), limiting recursion to true paths.
void	dispose() Disposes this document iterator, releasing all resources.
int	document() Returns the last document returned by nextDocument().
ReferenceSet<Index>	indices() Returns the set of indices over which this iterator is built.
IntervalIterator	intervalIterator() Returns the interval iterator of this document iterator for single-index queries.
IntervalIterator	intervalIterator(Index index) Returns the interval iterator of this document iterator for the given index.
Reference2ReferenceMap<Index,IntervalIterator>	intervalIterators() Returns an unmodifiable map from indices to interval iterators.
boolean	mayHaveNext() Returns whether there may be a next document, possibly with false positives.
int	nextDocument() Returns the next document provided by this document iterator, or END_OF_LIST if no more documents are available.
int	skipTo(int n) Skips all documents smaller than n.
double	weight() Returns the weight associated with this iterator.
DocumentIterator	weight(double weight) Sets the weight of this index iterator.

Field Detail

END_OF_LIST

static final int END_OF_LIST

A special value denoting that the end of the list has been reached.

See Also:

Constant Field Values

Method Detail

intervalIterator

IntervalIterator intervalIterator()
                                  throws IOException

Returns the interval iterator of this document iterator for single-index queries.

This is a commodity method that can be used only for queries built over a single index.

Returns:

an interval iterator.

Throws:

IllegalStateException - if this document iterator is not built on a single index.

IOException

See Also:

intervalIterator(Index)

intervalIterator

IntervalIterator intervalIterator(Index index)
                                  throws IOException

Returns the interval iterator of this document iterator for the given index.

After a call to nextDocument(), this iterator can be used to retrieve the intervals in the current document (the one returned by nextDocument()) for the index index.

Note that if all indices have positions, it is guaranteed that at least one index will return an interval. However, for disjunctive queries it cannot be guaranteed that all indices will return an interval.

Indices without positions always return IntervalIterators.TRUE. Thus, in presence of indices without positions it is possible that no intervals at all are available.

Parameters:

index - an index (must be one over which the query was built).

Returns:

an interval iterator over the current document in index.

Throws:

IOException

intervalIterators

Reference2ReferenceMap<Index,IntervalIterator> intervalIterators()
                                                                 throws IOException

Returns an unmodifiable map from indices to interval iterators.

After a call to nextDocument(), this map can be used to retrieve the intervals in the current document. An invocation of Map.get(java.lang.Object) on this map with argument index yields the same result as intervalIterator(index).

Returns:

a map from indices to interval iterators over the current document.

Throws:

UnsupportedOperationException - if this index does not contain positions.

IOException

See Also:

intervalIterator(Index)

indices

ReferenceSet<Index> indices()

Returns the set of indices over which this iterator is built.

Returns:

the set of indices over which this iterator is built.

nextDocument

int nextDocument()
                 throws IOException

Returns the next document provided by this document iterator, or END_OF_LIST if no more documents are available.

Returns:

the next document, or END_OF_LIST if no more documents are available.

Throws:

IOException

mayHaveNext

boolean mayHaveNext()

Returns whether there may be a next document, possibly with false positives.

Returns:

true there may be a next document; false if certainly there is no next document.

document

int document()

Returns the last document returned by nextDocument().

Returns:

the last document returned by nextDocument(), -1 if no document has been returned yet, and END_OF_LIST if the list of results has been exhausted.

skipTo

int skipTo(int n)
           throws IOException

Skips all documents smaller than n.

Define the current document k associated with this document iterator as follows:

• -1, if nextDocument() and this method have never been called;
• END_OF_LIST, if a call to this method or to nextDocument() returned END_OF_LIST;
• the last value returned by a call to nextDocument() or this method, otherwise.

If k is larger than or equal to n, then this method does nothing and returns k. Otherwise, a call to this method is equivalent to

 while( ( k = nextDocument() ) < n );
 return k;
 

Thus, when a result k ≠ END_OF_LIST is returned, the state of this iterator will be exactly the same as after a call to nextDocument() that returned k. In particular, the first document larger than or equal to n (when returned by this method) will not be returned by the next call to nextDocument().

Parameters:

n - a document pointer.

Returns:

a document pointer larger than or equal to n if available, END_OF_LIST otherwise.

Throws:

IOException

accept

<T> T accept(DocumentIteratorVisitor<T> visitor)
         throws IOException

Accepts a visitor.

A document iterator is usually structured as composite, with operators as internal nodes and IndexIterators as leaves. This method implements the visitor pattern.

Parameters:

visitor - the visitor.

Returns:

an object resulting from the visit, or null if the visit was interrupted.

Throws:

IOException

acceptOnTruePaths

<T> T acceptOnTruePaths(DocumentIteratorVisitor<T> visitor)
                    throws IOException

Accepts a visitor after a call to nextDocument(), limiting recursion to true paths.

After a call to nextDocument(), a document iterator is positioned over a document. This call is equivalent to accept(DocumentIteratorVisitor), but visits only along true paths.

We define a true path as a path from the root of the composite that passes only through nodes whose associated subtree is positioned on the same document of the root. Note that OrDocumentIterators detach exhausted iterators from the composite tree, so true paths define the subtree that is causing the current document to satisfy the query represented by this document iterator.

For more elaboration, and the main application of this method, see CounterCollectionVisitor.

Parameters:

visitor - the visitor.

Returns:

an object resulting from the visit, or null if the visit was interrupted.

Throws:

IOException

See Also:

accept(DocumentIteratorVisitor), CounterCollectionVisitor

weight

double weight()

Returns the weight associated with this iterator.

The number returned by this method has no fixed semantics: different scorers might choose different interpretations, or even ignore it.

Returns:

the weight associated with this iterator.

weight

DocumentIterator weight(double weight)

Sets the weight of this index iterator.

Parameters:

weight - the weight of this index iterator.

Returns:

this document iterator.

dispose

void dispose()
             throws IOException

Disposes this document iterator, releasing all resources.

This method should propagate down to the underlying index iterators, where it should release resources such as open files and network connections. If you're doing your own resource tracking and pooling, then you do not need to call this method.

Throws:

IOException