MatchEngine
public class EqualsMatchEngine extends java.lang.Object implements MatchEngine
The equality is roughly in the sense of Object.equals(java.lang.Object)
,
but some additional work is done, so that for instance (multi-dimensional)
arrays are compared (recursively) on their contents, and blank objects
are compared in the sense used in the rest of STIL. A blank value is
not considered equal to anything, including another blank value.
Scalar numeric values are, as far as possible, compared on numeric
value rather than object equality, though this numeric value comparison
does not currently apply to arrays.
NO_BINS
Constructor | Description |
---|---|
EqualsMatchEngine() |
Modifier and Type | Method | Description |
---|---|---|
boolean |
canBoundMatch() |
Indicates that the
MatchEngine.getMatchBounds(uk.ac.starlink.table.join.NdRange[], int) method can be invoked
to provide some sort of useful result. |
java.lang.Object[] |
getBins(java.lang.Object[] tuple) |
Returns a set of keys for bins into which possible matches for
a given tuple might fall.
|
NdRange |
getMatchBounds(NdRange[] inRanges,
int index) |
Given a range of tuple values, returns a range outside which
no match to anything within that range can result.
|
DescribedValue[] |
getMatchParameters() |
Returns a set of DescribedValue objects whose values can be modified
to modify the matching criteria.
|
ValueInfo |
getMatchScoreInfo() |
The match score is uninteresting, since it's either -1 or 0.
|
double |
getScoreScale() |
Returns a scale value for the match score.
|
DescribedValue[] |
getTuningParameters() |
Returns a set of DescribedValue objects whose values can be modified
to tune the performance of the match.
|
ValueInfo[] |
getTupleInfos() |
Returns a set of ValueInfo objects indicating what is required for
the elements of each tuple.
|
double |
matchScore(java.lang.Object[] tuple1,
java.lang.Object[] tuple2) |
Indicates whether two tuples count as matching each other, and if
so how closely.
|
java.lang.String |
toString() |
public double matchScore(java.lang.Object[] tuple1, java.lang.Object[] tuple2)
MatchEngine
If there's no reason to do otherwise, the range 0..1 is recommended for successul matches. However, if the result has some sort of physical meaning (such as a distance in real space) that may be used instead.
matchScore
in interface MatchEngine
tuple1
- one tupletuple2
- the other tuplepublic double getScoreScale()
MatchEngine
matchScore
/MatchEngine.getScoreScale()
is of order unity, and is thus comparable between
different match engines.
As a general rule, the result should be the maximum value ever
returned from the matchScore
method,
corresponding to the least good successful match.
For binary MatchEngine implementations
(all matches are either score=0 or failures)
a value of 1 is recommended.
If nothing reliable can be said about the scale, NaN may be returned.
getScoreScale
in interface MatchEngine
public java.lang.Object[] getBins(java.lang.Object[] tuple)
MatchEngine
getBins
in interface MatchEngine
tuple
- tuplepublic ValueInfo getMatchScoreInfo()
null
here.getMatchScoreInfo
in interface MatchEngine
public ValueInfo[] getTupleInfos()
MatchEngine
getTupleInfos
in interface MatchEngine
public DescribedValue[] getMatchParameters()
MatchEngine
DescribedValue.setValue(java.lang.Object)
on the
returned objects.getMatchParameters
in interface MatchEngine
public DescribedValue[] getTuningParameters()
MatchEngine
DescribedValue.setValue(java.lang.Object)
on the
returned objects.
Changing these values will make no difference to the output of
MatchEngine.matchScore(java.lang.Object[], java.lang.Object[])
, but may change the output of MatchEngine.getBins(java.lang.Object[])
.
This may change the CPU and memory requirements of the match,
but will not change the result. The default value should be
something sensible, so that setting the value of these parameters
is not in general required.
getTuningParameters
in interface MatchEngine
public boolean canBoundMatch()
MatchEngine
MatchEngine.getMatchBounds(uk.ac.starlink.table.join.NdRange[], int)
method can be invoked
to provide some sort of useful result.canBoundMatch
in interface MatchEngine
public NdRange getMatchBounds(NdRange[] inRanges, int index)
MatchEngine
Both the input and output rectangles are specified by tuples representing its opposite corners; equivalently, they are the minimum and maximum values of each tuple element. In either the input or output min/max tuples, any element may be null to indicate that no information is available on the bounds of that tuple element (coordinate).
An array of n-dimensional ranges is given, though only one of them
(specified by the index
value) forms the basis for
the output range. The other ranges in the input array may in some
cases be needed as context in order to do the calculation.
If the match error is fixed, only the single input n-d range is needed
to work out the single output range. However, if the errors are
obtained by looking at the tuples themselves (match errors are per-row)
then in general the broadening has to be done using the maximum
error of any of the tables involved in the match,
not just the one to be broadened.
For a long time, I didn't realise this, so versions of this software
up to STIL v3.0-14 (Oct 2015) were not correctly broadening these
ranges, leading to potentially missed associations near the edge
of bounded regions.
This method can be used by match algorithms which know in advance the range of coordinates they will match against and wish to reduce workload by not attempting matches which are bound to fail.
For example, a 1-d Cartesian match engine with an isotropic match error 0.5 would turn input values of ((0,200),(10,210)) into output values ((-0.5,199.5),(10.5,210.5)).
This method will only be called if MatchEngine.canBoundMatch()
returns true. Thus engines that cannot provide any useful
information along these lines (for instance because none of its
tuple elements is Comparable
) do not need to
implement it in a meaningful way.
getMatchBounds
in interface MatchEngine
inRanges
- array of input ranges for the tables on which
the match will take place;
each element bounds the values for each tuple
element in its corresponding table
in a possible match
(to put it another way - each element gives the
coordinates of the opposite corners of a tuple-space
rectangle covered by one input table)index
- which element of the inRanges
array
for which the broadened output value is requiredinRanges[index]
broadened by errorsMatchEngine.canBoundMatch()
public java.lang.String toString()
toString
in class java.lang.Object
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