com.google.uzaygezen.core

Interface FilterCombiner<F,V,R>

Type Parameters:

T - filter type

All Known Implementing Classes:

ListConcatCombiner, PlainFilterCombiner

public interface FilterCombiner<F,V,R>

Combiner of two space filling curve index ranges with attached filters. Because the number of index ranges that a query expression must have is limited, this abstraction allows one to customise the operation of joining together two consecutive ranges, while still preserving some filtering of the extraneous data inside. Thus while the index ranges are an inclusive mechanism, this is the exclusive mechanism that works inside an index range.

Implementations are free to filter out all irrelevant data, or only some of it, if at all. If the former happens for each call, and in addition to that, the SpaceVisitor never returns SpatialRelation.COVERED when there is a chance for extraneous points in that particular orthotope, the framework guarantees that that no irrelevant data points will be selected by the query. On the other hand, if the filter object stats getting too big, an implementation is free to create a filter that doesn't filter anything at all. But in that case extraneous points might (and probably will) be selected by the constructed query.

Author:

Daniel Aioanei

Method Summary

Methods

Modifier and Type	Method and Description
SelectiveFilter<F>	combine(FilteredIndexRange<F,R> firstFilteredRange, FilteredIndexRange<F,R> secondFilteredRange, V gapEstimate) Combines two filtered index ranges and produces a combined filter that must be valid in the context of the range [firstFilteredRange.getIndexRange().getStart(), secondFilteredRange.getIndexRange().getEnd()).

Method Detail

combine

SelectiveFilter<F> combine(FilteredIndexRange<F,R> firstFilteredRange,
                         FilteredIndexRange<F,R> secondFilteredRange,
                         V gapEstimate)

Combines two filtered index ranges and produces a combined filter that must be valid in the context of the range [firstFilteredRange.getIndexRange().getStart(), secondFilteredRange.getIndexRange().getEnd()). When the framework calls this method it is guaranteed that firstRange is disjoint and sits before secondIndexRange on the space filling curve.

The parameter gapEstimate is provided to help implementations trade the size of the filter in some representation format for selectivity of irrelevant points, and to enabled heavy optimisations free of any tradeoffs when the gap is zero.

Parameters:

firstFilteredRange - the filtered index range coming before on the space filling curve

secondFilteredRange - the filtered index range coming after on the space filling curve

gapEstimate - the estimate of the number of points in the gap between the index ranges. If zero, then it is guaranteed that there are no data points in between. If non zero, it is just an estimate and its accuracy depends on the accuracy provided by the RegionInspector in use. If the two ranges are adjacent, i.e. firstFilteredRange.getIndexRange().getEnd() == secondFilteredRange.getIndexRange().getStart(), then the gap estimate is guaranteed to be zero.

Returns:

the combined filter and a bool value specifying if potential over selectivity might result by replacing the two filtered ranges with one range with the combined filter attached