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NullOperator Class

Represents a part of the algebra that has been determined to not return any results in advance and so can be replaced with this operator which always returns null.
Inheritance Hierarchy
SystemObject
  VDS.RDF.Query.AlgebraNullOperator

Namespace:  VDS.RDF.Query.Algebra
Assembly:  dotNetRDF (in dotNetRDF.dll) Version:
Syntax
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public class NullOperator : ISparqlAlgebra, 
	ITerminalOperator

The NullOperator type exposes the following members.

Constructors
  NameDescription
Public methodNullOperator
Creates a new Null Operator.
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Properties
  NameDescription
Public propertyFixedVariables
Gets the enumeration of fixed variables in the algebra i.e. variables that are guaranteed to have a bound value.
Public propertyFloatingVariables
Gets the enumeration of floating variables in the algebra i.e. variables that are not guaranteed to have a bound value.
Public propertyVariables
Gets the variables used in this algebra.
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Methods
  NameDescription
Public methodEquals
Determines whether the specified object is equal to the current object.
(Inherited from Object.)
Public methodEvaluate
Evaluates the Null operator which of course always returns a NullMultiset.
Protected methodFinalize
Allows an object to try to free resources and perform other cleanup operations before it is reclaimed by garbage collection.
(Inherited from Object.)
Public methodGetHashCode
Serves as the default hash function.
(Inherited from Object.)
Public methodGetType
Gets the Type of the current instance.
(Inherited from Object.)
Protected methodMemberwiseClone
Creates a shallow copy of the current Object.
(Inherited from Object.)
Public methodToGraphPattern
Throws an error since a null operator cannot be transformed back into a query.
Public methodToQuery
Throws an error since a null operator cannot be transformed back into a query.
Public methodToString
Gets the string representation of the algebra.
(Overrides ObjectToString.)
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Remarks
Primarily intended for use with Algebra Optimisers which are rewriting the algebra to run against an out of memory dataset (e.g. SQL based) where it may be easily possible to determine if a triple pattern will match in advance of actually returning the matches.
See Also