ai.grakn.graql.internal.gremlin.fragment

Class Fragment

java.lang.Object

ai.grakn.graql.internal.gremlin.fragment.Fragment

Direct Known Subclasses:

AbstractRolePlayerFragment

public abstract class Fragment
extends Object

represents a graph traversal, with one start point and optionally an end point

A fragment is composed of four things:

• A gremlin traversal function, that takes a gremlin traversal and appends some new gremlin steps
• A starting variable name, where the gremlin traversal must start from
• An optional ending variable name, if the gremlin traversal navigates to a new Graql variable
• A priority, that describes how efficient this traversal is to help with ordering the traversals

Variable names refer to Graql variables. Some of these variable names may be randomly-generated UUIDs, such as for castings.

A Fragment is usually contained in a EquivalentFragmentSet, which contains multiple fragments describing the different directions the traversal can be followed in, with different starts and ends.

A gremlin traversal is created from a Query by appending together fragments in order of priority, one from each EquivalentFragmentSet describing the Query.

Author:

Felix Chapman

Property Summary

Type	Property and Description
abstract VarProperty	var Get the corresponding property

Constructor Summary

Constructors

Constructor and Description
Fragment()

Method Summary

Modifier and Type	Method and Description
org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal<org.apache.tinkerpop.gremlin.structure.Vertex,? extends org.apache.tinkerpop.gremlin.structure.Element>	applyTraversal(org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal<org.apache.tinkerpop.gremlin.structure.Vertex,? extends org.apache.tinkerpop.gremlin.structure.Element> traversal, GraknTx graph, Collection<Var> vars, Var currentVar)
boolean	canOperateOnEdges() Indicates whether the fragment can be used on an Edge as well as a Vertex.
Set<Var>	dependencies()
Set<Weighted<DirectedEdge<Node>>>	directedEdges(Map<NodeId,Node> nodes, Map<Node,Map<Node,Fragment>> edges) Convert the fragment to a set of weighted edges for query planning
Var	end()
abstract double	fragmentCost() Get the cost for executing the fragment.
boolean	hasFixedFragmentCost() If a fragment has fixed cost, the traversal is done using index.
boolean	isStartingFragment() A starting fragment is a fragment that can start a traversal.
abstract String	name() The name of the fragment
abstract Var	start()
String	toString()
abstract VarProperty	varProperty() Get the corresponding property
Set<Var>	vars() Get all variables in the fragment including the start and end (if present)

Methods inherited from class java.lang.Object

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

Property Detail

var

@Nullable
public abstract VarProperty varProperty

Get the corresponding property

Constructor Detail

Fragment

public Fragment()

Method Detail

varProperty

@Nullable
public abstract VarProperty varProperty()

Get the corresponding property

start

public abstract Var start()

Returns:

the variable name that this fragment starts from in the query

end

@Nullable
public Var end()

Returns:

the variable name that this fragment ends at in the query, if this query has an end variable

dependencies

public Set<Var> dependencies()

Returns:

the variable names that this fragment requires to have already been visited

directedEdges

public Set<Weighted<DirectedEdge<Node>>> directedEdges(Map<NodeId,Node> nodes,
                                                       Map<Node,Map<Node,Fragment>> edges)

Convert the fragment to a set of weighted edges for query planning

Parameters:

nodes - all nodes in the query

edges - a mapping from edge(child, parent) to its corresponding fragment

Returns:

a set of edges

applyTraversal

public final org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal<org.apache.tinkerpop.gremlin.structure.Vertex,? extends org.apache.tinkerpop.gremlin.structure.Element> applyTraversal(org.apache.tinkerpop.gremlin.process.traversal.dsl.graph.GraphTraversal<org.apache.tinkerpop.gremlin.structure.Vertex,? extends org.apache.tinkerpop.gremlin.structure.Element> traversal,
                                                                                                                                                                                                            GraknTx graph,
                                                                                                                                                                                                            Collection<Var> vars,
                                                                                                                                                                                                            @Nullable
                                                                                                                                                                                                            Var currentVar)

Parameters:

traversal - the traversal to extend with this Fragment

graph - the graph to execute the traversal on

name

public abstract String name()

The name of the fragment

isStartingFragment

public boolean isStartingFragment()

A starting fragment is a fragment that can start a traversal. If any other fragment is present that refers to the same variable, the starting fragment can be omitted.

fragmentCost

public abstract double fragmentCost()

Get the cost for executing the fragment.

hasFixedFragmentCost

public boolean hasFixedFragmentCost()

If a fragment has fixed cost, the traversal is done using index. This makes the fragment a good starting point. A plan should always start with these fragments when possible.

canOperateOnEdges

public boolean canOperateOnEdges()

Indicates whether the fragment can be used on an Edge as well as a Vertex.

vars

public final Set<Var> vars()

Get all variables in the fragment including the start and end (if present)

toString

public final String toString()

Overrides:

toString in class Object