org.eclipse.viatra.query.runtime.api

Class ViatraQueryEngine

java.lang.Object

org.eclipse.viatra.query.runtime.api.ViatraQueryEngine

Direct Known Subclasses:

AdvancedViatraQueryEngine

public abstract class ViatraQueryEngine
extends java.lang.Object

A Viatra Query (incremental) evaluation engine, attached to a model such as an EMF resource. The engine hosts pattern matchers, and will listen on model update notifications stemming from the given model in order to maintain live results.

By default, ViatraQueryEngines do not need to be separately disposed; they will be garbage collected along with the model. Advanced users: see AdvancedViatraQueryEngine if you want fine control over the lifecycle of an engine.

Pattern matchers within this engine may be instantiated in the following ways:

• Recommended: instantiate the specific matcher class generated for the pattern by e.g. MyPatternMatcher.on(engine).
• Use getMatcher(IQuerySpecification) if the pattern-specific generated matcher API is not available.
• Advanced: use the query specification associated with the generated matcher class to achieve the same.

Additionally, a group of patterns (see IQueryGroup) can be initialized together before usage; this may improve the performance of pattern matcher construction by trying to gather all necessary information from the model in one go. Note that no such improvement is to be expected if the engine is specifically constructed in wildcard mode, an option available in some scope implementations (see EMFScope.EMFScope(Notifier, BaseIndexOptions) and BaseIndexOptions.withWildcardMode(boolean)).

No Extend:

This class is not intended to be subclassed by clients.

Constructor Summary

Constructors

Constructor and Description
ViatraQueryEngine()

Method Summary

Modifier and Type	Method and Description
abstract IBaseIndex	getBaseIndex() Provides access to the internal base index component of the engine, responsible for keeping track of basic contents of the model.
abstract java.util.Set<? extends ViatraQueryMatcher<? extends IPatternMatch>>	getCurrentMatchers() Access a copy of available ViatraQueryMatcher pattern matchers.
abstract <Matcher extends ViatraQueryMatcher<? extends IPatternMatch>> Matcher	getExistingMatcher(IQuerySpecification<Matcher> querySpecification) Access an existing pattern matcher based on a IQuerySpecification.
abstract <Matcher extends ViatraQueryMatcher<? extends IPatternMatch>> Matcher	getMatcher(IQuerySpecification<Matcher> querySpecification) Access a pattern matcher based on a IQuerySpecification.
abstract ViatraQueryMatcher<? extends IPatternMatch>	getMatcher(java.lang.String patternFQN) Access a pattern matcher for the graph pattern with the given fully qualified name.
java.util.Set<IQuerySpecification<? extends ViatraQueryMatcher<? extends IPatternMatch>>>	getRegisteredQuerySpecifications()
abstract QueryScope	getScope()
static ViatraQueryEngine	on(QueryScope scope) Obtain a (managed) ViatraQueryEngine to evaluate queries over a given scope specified by an QueryScope.
static ViatraQueryEngine	on(QueryScope scope, ViatraQueryEngineOptions options) Obtain a (managed) ViatraQueryEngine to evaluate queries over a given scope specified by an QueryScope.

Methods inherited from class java.lang.Object

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

Constructor Detail

ViatraQueryEngine

public ViatraQueryEngine()

Method Detail

on

public static ViatraQueryEngine on(QueryScope scope)
                            throws ViatraQueryException

Obtain a (managed) ViatraQueryEngine to evaluate queries over a given scope specified by an QueryScope.

For a given matcher scope, the same engine will be returned to any client. This facilitates the reuse of internal caches of the engine, greatly improving performance.

The lifecycle of this engine is centrally managed, and will not be disposed as long as the model is retained in memory. The engine will be garbage collected along with the model.

Advanced users: see AdvancedViatraQueryEngine.createUnmanagedEngine(QueryScope) to obtain a private, unmanaged engine that is not shared with other clients and allows tight control over its lifecycle.

Parameters:

scope - the scope of query evaluation; the definition of the set of model elements that this engine is operates on. Provide e.g. a EMFScope for evaluating queries on an EMF model.

Returns:

a (managed) ViatraQueryEngine instance

Throws:

ViatraQueryException - on initialization errors.

on

public static ViatraQueryEngine on(QueryScope scope,
                                   ViatraQueryEngineOptions options)
                            throws ViatraQueryException

Obtain a (managed) ViatraQueryEngine to evaluate queries over a given scope specified by an QueryScope.

For a given matcher scope, the same engine will be returned to any client. This facilitates the reuse of internal caches of the engine, greatly improving performance.

The lifecycle of this engine is centrally managed, and will not be disposed as long as the model is retained in memory. The engine will be garbage collected along with the model.

Advanced users: see AdvancedViatraQueryEngine.createUnmanagedEngine(QueryScope) to obtain a private, unmanaged engine that is not shared with other clients and allows tight control over its lifecycle.

Parameters:

scope - the scope of query evaluation; the definition of the set of model elements that this engine is operates on. Provide e.g. a EMFScope for evaluating queries on an EMF model.

Returns:

a (managed) ViatraQueryEngine instance

Throws:

ViatraQueryException - on initialization errors.

Since:

1.4

getBaseIndex

public abstract IBaseIndex getBaseIndex()
                                 throws ViatraQueryException

Provides access to the internal base index component of the engine, responsible for keeping track of basic contents of the model.

If using an EMFScope, consider EMFScope.extractUnderlyingEMFIndex(ViatraQueryEngine) instead to access EMF-specific details.

Returns:

the baseIndex the NavigationHelper maintaining the base index

Throws:

ViatraQueryException - if the base index could not be constructed

getMatcher

public abstract <Matcher extends ViatraQueryMatcher<? extends IPatternMatch>> Matcher getMatcher(IQuerySpecification<Matcher> querySpecification)
                                                                                          throws ViatraQueryException

Access a pattern matcher based on a IQuerySpecification. Multiple calls will return the same matcher.

Parameters:

querySpecification - a IQuerySpecification that describes a VIATRA query specification

Returns:

a pattern matcher corresponding to the specification

Throws:

ViatraQueryException - if the matcher could not be initialized

getMatcher

public abstract ViatraQueryMatcher<? extends IPatternMatch> getMatcher(java.lang.String patternFQN)
                                                                throws ViatraQueryException

Access a pattern matcher for the graph pattern with the given fully qualified name. Will succeed only if a query specification for this fully qualified name has been generated and registered. Multiple calls will return the same matcher unless the registered specification changes.

Parameters:

patternFQN - the fully qualified name of a VIATRA query specification

Returns:

a pattern matcher corresponding to the specification

Throws:

ViatraQueryException - if the matcher could not be initialized

getExistingMatcher

public abstract <Matcher extends ViatraQueryMatcher<? extends IPatternMatch>> Matcher getExistingMatcher(IQuerySpecification<Matcher> querySpecification)

Access an existing pattern matcher based on a IQuerySpecification.

Parameters:

querySpecification - a IQuerySpecification that describes a VIATRA query specification

Returns:

a pattern matcher corresponding to the specification, null if a matcher does not exist yet.

getCurrentMatchers

public abstract java.util.Set<? extends ViatraQueryMatcher<? extends IPatternMatch>> getCurrentMatchers()

Access a copy of available ViatraQueryMatcher pattern matchers.

Returns:

a copy of the set of currently available pattern matchers registered on this engine instance

getRegisteredQuerySpecifications

public java.util.Set<IQuerySpecification<? extends ViatraQueryMatcher<? extends IPatternMatch>>> getRegisteredQuerySpecifications()

getScope

public abstract QueryScope getScope()

Returns:

the scope of query evaluation; the definition of the set of model elements that this engine is operates on.