# Package org.apache.lucene.search.spans

The calculus of spans.

See: Description

- Interface Summary
  Interface | Description
  --- | ---
  SpanCollector | An interface defining the collection of postings information from the leaves of a `Spans`

- Class Summary
  Class | Description
  --- | ---
  FieldMaskingSpanQuery | Wrapper to allow `SpanQuery` objects participate in composite single-field SpanQueries by 'lying' about their search field.
  FilterSpans | A `Spans` implementation wrapping another spans instance, allowing to filter spans matches easily by implementing `FilterSpans.accept(org.apache.lucene.search.spans.Spans)`
  NearSpansOrdered | A Spans that is formed from the ordered subspans of a SpanNearQuery where the subspans do not overlap and have a maximum slop between them.
  NearSpansUnordered | Similar to `NearSpansOrdered`, but for the unordered case.
  SpanBoostQuery | Counterpart of `BoostQuery` for spans.
  SpanContainingQuery | Keep matches that contain another SpanScorer.
  SpanFirstQuery | Matches spans near the beginning of a field.
  SpanMultiTermQueryWrapper<Q extends MultiTermQuery> | Wraps any `MultiTermQuery` as a `SpanQuery`, so it can be nested within other SpanQuery classes.
  SpanMultiTermQueryWrapper.SpanRewriteMethod | Abstract class that defines how the query is rewritten.
  SpanMultiTermQueryWrapper.TopTermsSpanBooleanQueryRewrite | A rewrite method that first translates each term into a SpanTermQuery in a `BooleanClause.Occur.SHOULD` clause in a BooleanQuery, and keeps the scores as computed by the query.
  SpanNearQuery | Matches spans which are near one another.
  SpanNearQuery.Builder | A builder for SpanNearQueries
  SpanNotQuery | Removes matches which overlap with another SpanQuery or which are within x tokens before or y tokens after another SpanQuery.
  SpanOrQuery | Matches the union of its clauses.
  SpanPositionCheckQuery | Base class for filtering a SpanQuery based on the position of a match.
  SpanPositionRangeQuery | Checks to see if the `SpanPositionCheckQuery.getMatch()` lies between a start and end position See `SpanFirstQuery` for a derivation that is optimized for the case where start position is 0.
  SpanQuery | Base class for span-based queries.
  Spans | Iterates through combinations of start/end positions per-doc.
  SpanScorer | A basic `Scorer` over `Spans`.
  SpanTermQuery | Matches spans containing a term.
  SpanWeight | Expert-only.
  SpanWithinQuery | Keep matches that are contained within another Spans.
  TermSpans | Expert: Public for extension only.

- Enum Summary
  Enum | Description
  --- | ---
  FilterSpans.AcceptStatus | Status returned from `FilterSpans.accept(Spans)` that indicates whether a candidate match should be accepted, rejected, or rejected and move on to the next document.
  SpanWeight.Postings | Enumeration defining what postings information should be retrieved from the index for a given Spans

## Package org.apache.lucene.search.spans Description

The calculus of spans.

A span is a `<doc,startPosition,endPosition>` tuple that is enumerated by class `Spans`.

The following span query operators are implemented:

- A `SpanTermQuery` matches all spans containing a particular `Term`. This should not be used for terms that are indexed at position Integer.MAX_VALUE.
- A `SpanNearQuery` matches spans which occur near one another, and can be used to implement things like phrase search (when constructed from `SpanTermQuery`s) and inter-phrase proximity (when constructed from other `SpanNearQuery`s).
- A `SpanWithinQuery` matches spans which occur inside of another spans.
- A `SpanContainingQuery` matches spans which contain another spans.
- A `SpanOrQuery` merges spans from a number of other `SpanQuery`s.
- A `SpanNotQuery` removes spans matching one `SpanQuery` which overlap (or comes near) another. This can be used, e.g., to implement within-paragraph search.
- A `SpanFirstQuery` matches spans matching `q` whose end position is less than `n`. This can be used to constrain matches to the first part of the document.
- A `SpanPositionRangeQuery` is a more general form of SpanFirstQuery that can constrain matches to arbitrary portions of the document.

In all cases, output spans are minimally inclusive. In other words, a span formed by matching a span in x and y starts at the lesser of the two starts and ends at the greater of the two ends.

For example, a span query which matches "John Kerry" within ten words of "George Bush" within the first 100 words of the document could be constructed with:

     SpanQuery john   = new SpanTermQuery(new Term("content", "john"));
     SpanQuery kerry  = new SpanTermQuery(new Term("content", "kerry"));
     SpanQuery george = new SpanTermQuery(new Term("content", "george"));
     SpanQuery bush   = new SpanTermQuery(new Term("content", "bush"));

     SpanQuery johnKerry =
        new SpanNearQuery(new SpanQuery[] {john, kerry}, 0, true);

     SpanQuery georgeBush =
        new SpanNearQuery(new SpanQuery[] {george, bush}, 0, true);

     SpanQuery johnKerryNearGeorgeBush =
        new SpanNearQuery(new SpanQuery[] {johnKerry, georgeBush}, 10, false);

     SpanQuery johnKerryNearGeorgeBushAtStart =
        new SpanFirstQuery(johnKerryNearGeorgeBush, 100);

Span queries may be freely intermixed with other Lucene queries. So, for example, the above query can be restricted to documents which also use the word "iraq" with:

     Query query = new BooleanQuery();
     query.add(johnKerryNearGeorgeBushAtStart, true, false);
     query.add(new TermQuery("content", "iraq"), true, false);

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