uk.ac.starlink.table.join

Class EqualsMatchEngine

java.lang.Object

uk.ac.starlink.table.join.EqualsMatchEngine

All Implemented Interfaces:

MatchEngine

public class EqualsMatchEngine
extends Object
implements MatchEngine

Match engine which considers two rows matched if they contain objects which are non-blank and equal. The objects will typically be strings, but could equally be something else. Match scores are always either 0.0 (equal) or -1.0 (unequal).

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.

Since:

25 Mar 2004

Author:

Mark Taylor (Starlink)

Constructor Summary

Constructors

Constructor and Description
EqualsMatchEngine()

Method Summary

Modifier and Type	Method and Description
java.util.function.Supplier<Coverage>	createCoverageFactory() Returns null.
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() 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.
String	toString()

Methods inherited from class java.lang.Object

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

Constructor Detail

EqualsMatchEngine

public EqualsMatchEngine()

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()

Returns null. You could check bounds on hashcodes, but it's not likely to be very revealing.

Specified by:

createCoverageFactory in interface MatchEngine

Returns:

supplier of coverage objects, or null

getScoreScale

public double getScoreScale()

Description copied from interface: MatchEngine

Returns a scale value for the match score. The intention is that the result of 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.

Specified by:

getScoreScale in interface MatchEngine

Returns:

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

getMatchScoreInfo

public ValueInfo getMatchScoreInfo()

The match score is uninteresting, since it's either -1 or 0. We flag this by returning null here.

Specified by:

getMatchScoreInfo in interface MatchEngine

Returns:

null

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

toString

public String toString()

Overrides:

toString in class Object