uk.ac.starlink.table.join

Class CombinedMatchEngine

java.lang.Object

uk.ac.starlink.table.join.CombinedMatchEngine

All Implemented Interfaces:

MatchEngine

public class CombinedMatchEngine
extends Object
implements MatchEngine

A matching engine which provides matching facilities by combining the characteristics of a number of other matching engines.

The tuples accepted by this engine are composed of the tuples of its constituent engines (as specified by the engines argument of the constructor) concatenated in sequence.

The match score is formed by taking the scaled match scores of the constituent engines and adding them in quadrature (if no scaling is available, unscaled values are used). Versions of this class before 2017 did not do that, it just added unscaled match scores together, which doesn't make much sense.

Because of the way it calculates bins (taking a Cartesian product of one bin array by another), it is a good idea for efficiency's sake to keep down the number of bins returned by the MatchKit.getBins(java.lang.Object[]) method of the constituent match engines.

Author:

Mark Taylor (Starlink)

Constructor Summary

Constructors

Constructor and Description
CombinedMatchEngine(MatchEngine[] engines) Constructs a CombinedMatchEngine with default sphere inclusion semantics.
CombinedMatchEngine(MatchEngine[] engines, boolean inSphere) Constructs a CombinedMatchEngine with specified sphere inclusion semantics.

Method Summary

Modifier and Type	Method and Description
java.util.function.Supplier<Coverage>	createCoverageFactory() Returns a supplier for coverage objects.
java.util.function.Supplier<MatchKit>	createMatchKitFactory() Returns a factory for MatchKit instances corresponding to the current settings of this object.
DescribedValue[]	getMatchParameters() Returns a set of DescribedValue objects whose values can be modified to modify the matching criteria.
ValueInfo	getMatchScoreInfo() Returns a description of the value returned by the MatchKit.matchScore(java.lang.Object[], java.lang.Object[]) method.
double	getScoreScale() Returns the square root of the number of constituent matchers if they all have definite score scaling values.
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.
void	setName(String name)
String	toString()

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Constructor Detail

CombinedMatchEngine

public CombinedMatchEngine(MatchEngine[] engines)

Constructs a CombinedMatchEngine with default sphere inclusion semantics.

Parameters:

engines - match engine sequence to be combined

CombinedMatchEngine

public CombinedMatchEngine(MatchEngine[] engines,
                           boolean inSphere)

Constructs a CombinedMatchEngine with specified sphere inclusion semantics.

If the inSphere parameter is false, any pair which is matched by all its constituent matchers counts as a match. If it is true, an additional constraint is imposed which is that the scaled separation (the match score) must be less than or equal to unity, that is the separation vector must be within the unit hyper-sphere rather than the unit hyper-cube.

Parameters:

engines - match engine sequence to be combined

inSphere - whether to restrict matches to those with separation values not exeeding unity

Method Detail

createMatchKitFactory

public java.util.function.Supplier<MatchKit> createMatchKitFactory()

Description copied from interface: MatchEngine

Returns a factory for MatchKit instances corresponding to the current settings of this object.

The returned value is immutable, and is not affected by subsequent changes of the settings of this object.

Specified by:

createMatchKitFactory in interface MatchEngine

Returns:

match kit supplier

createCoverageFactory

public java.util.function.Supplier<Coverage> createCoverageFactory()

Description copied from interface: MatchEngine

Returns a supplier for coverage objects. Each such coverage can be used to characterise a region of tuple space. When populated with a set of tuples A, any tuple for which the inclusion function defined by its Coverage.createTestFactory() method returns false is guaranteed not to match any tuple in A according to this object's match criteria.

The returned value is immutable, and is not affected by subsequent changes of the settings of this object.

If no suitable implementation is available, null may be returned.

Specified by:

createCoverageFactory in interface MatchEngine

Returns:

supplier of coverage objects, or null

getScoreScale

public double getScoreScale()

Returns the square root of the number of constituent matchers if they all have definite score scaling values. Otherwise, returns NaN.

Specified by:

getScoreScale in interface MatchEngine

Returns:

scale of successful match scores, a positive finite number or NaN

getMatchScoreInfo

public ValueInfo getMatchScoreInfo()

Description copied from interface: MatchEngine

Returns a description of the value returned by the MatchKit.matchScore(java.lang.Object[], java.lang.Object[]) method. The content class should be numeric (though need not be Double), and the name, description and units should be descriptive of whatever the physical significance of the value is. If the result of matchScore is not interesting (for instance, if it's always either 0 or -1), null may be returned.

Specified by:

getMatchScoreInfo in interface MatchEngine

Returns:

metadata for the match score results

getTupleInfos

public ValueInfo[] getTupleInfos()

Description copied from interface: MatchEngine

Returns a set of ValueInfo objects indicating what is required for the elements of each tuple. The length of this array is the number of elements in the tuple. Each element should at least have a defined name and content class. The info's nullable attribute has a special meaning: if true it means that it makes sense for this element of the tuple to be always blank (for instance assigned to no column).

Specified by:

getTupleInfos in interface MatchEngine

Returns:

array of objects describing the requirements on each element of the tuples used for matching

getMatchParameters

public DescribedValue[] getMatchParameters()

Description copied from interface: MatchEngine

Returns a set of DescribedValue objects whose values can be modified to modify the matching criteria. Typically at least one of these will be some sort of tolerance separation which determines how close tuples must be to count as a match. This match engine's behaviour can be modified by calling DescribedValue.setValue(java.lang.Object) on the returned objects.

Specified by:

getMatchParameters in interface MatchEngine

Returns:

array of described values which influence the match

getTuningParameters

public DescribedValue[] getTuningParameters()

Description copied from interface: MatchEngine

Returns a set of DescribedValue objects whose values can be modified to tune the performance of the match. This match engine's performance can be influenced by calling DescribedValue.setValue(java.lang.Object) on the returned objects.

Changing these values will make no difference to the output of MatchKit.matchScore(java.lang.Object[], java.lang.Object[]), but may change the output of MatchKit.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.

Specified by:

getTuningParameters in interface MatchEngine

Returns:

array of described values which may influence match performance

setName

public void setName(String name)

toString

public String toString()

Overrides:

toString in class Object