Class NullOperator

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
System.Object
NullOperator
Implements
Inherited Members
object.Equals(object)
object.Equals(object, object)
object.GetHashCode()
object.GetType()
object.MemberwiseClone()
object.ReferenceEquals(object, object)
Namespace: VDS.RDF.Query.Algebra
Assembly: dotNetRdf.dll
Syntax
public class NullOperator : ITerminalOperator, ISparqlAlgebra, IVisitable, IProcessable
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.

Constructors

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NullOperator(IEnumerable<string>)

Creates a new Null Operator.

Declaration
public NullOperator(IEnumerable<string> variables)
Parameters
Type Name Description
System.Collections.Generic.IEnumerable<T><string> variables

Variables in the algebra that this null is replacing.
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.

Properties

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FixedVariables

Gets the enumeration of fixed variables in the algebra i.e. variables that are guaranteed to have a bound value.

Declaration
public IEnumerable<string> FixedVariables { get; }
Property Value
Type Description
System.Collections.Generic.IEnumerable<T><string>
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.

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FloatingVariables

Gets the enumeration of floating variables in the algebra i.e. variables that are not guaranteed to have a bound value.

Declaration
public IEnumerable<string> FloatingVariables { get; }
Property Value
Type Description
System.Collections.Generic.IEnumerable<T><string>
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.

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Variables

Gets the variables used in this algebra.

Declaration
public IEnumerable<string> Variables { get; }
Property Value
Type Description
System.Collections.Generic.IEnumerable<T><string>
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.

Methods

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Accept<T>(ISparqlAlgebraVisitor<T>)

Declaration
public T Accept<T>(ISparqlAlgebraVisitor<T> visitor)
Parameters
Type Name Description
ISparqlAlgebraVisitor<T> visitor
Returns
Type Description
T
Type Parameters
Name Description
T
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.

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Accept<TResult, TContext>(ISparqlQueryAlgebraProcessor<TResult, TContext>, TContext)

Declaration
public TResult Accept<TResult, TContext>(ISparqlQueryAlgebraProcessor<TResult, TContext> processor, TContext context)
Parameters
Type Name Description
ISparqlQueryAlgebraProcessor<TResult, TContext> processor
TContext context
Returns
Type Description
TResult
Type Parameters
Name Description
TResult
TContext
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.

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ToGraphPattern()

Throws an error since a null operator cannot be transformed back into a query.

Declaration
public GraphPattern ToGraphPattern()
Returns
Type Description
GraphPattern
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.

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ToQuery()

Throws an error since a null operator cannot be transformed back into a query.

Declaration
public SparqlQuery ToQuery()
Returns
Type Description
SparqlQuery
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.

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ToString()

Gets the string representation of the algebra.

Declaration
public override string ToString()
Returns
Type Description
string
Overrides
object.ToString()
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.

Implements

Extension Methods