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diff --git a/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/matchers/backend/IQueryBackend.java b/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/matchers/backend/IQueryBackend.java
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+++ b/subprojects/viatra-runtime/src/main/java/tools/refinery/viatra/runtime/matchers/backend/IQueryBackend.java
@@ -0,0 +1,68 @@
+/*******************************************************************************
+ * Copyright (c) 2010-2014, Bergmann Gabor, Istvan Rath and Daniel Varro
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-v20.html.
+ * 
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+package tools.refinery.viatra.runtime.matchers.backend;
+
+import tools.refinery.viatra.runtime.matchers.ViatraQueryRuntimeException;
+import tools.refinery.viatra.runtime.matchers.psystem.queries.PQuery;
+
+/**
+ * Internal interface for a VIATRA query specification. Each query is associated with a pattern. Methods instantiate a matcher
+ * of the pattern with various parameters.
+ *
+ * @author Bergmann Gábor
+ * @since 0.9
+ * @noextend This interface is not intended to be extended by users of the VIATRA framework, and should only be used by the query engine
+ */
+public interface IQueryBackend {
+        
+        /**
+         * @return true iff this backend is incremental, i.e. it caches the results of queries for quick retrieval, 
+         * and can provide update notifications on result set changes.
+         */
+        public boolean isCaching();
+        
+    /**
+     * Returns a result provider for a given query. Repeated calls may return the same instance.
+     * @throws ViatraQueryRuntimeException
+     */
+        public IQueryResultProvider getResultProvider(PQuery query);
+        
+        /**
+     * Returns a result provider for a given query. Repeated calls may return the same instance.
+     * @param optional hints that may override engine and query defaults (as provided by {@link IQueryBackendHintProvider}). Can be null.
+     * @throws ViatraQueryRuntimeException 
+         * @since 1.4
+     */
+    public IQueryResultProvider getResultProvider(PQuery query, QueryEvaluationHint hints);
+        
+    /**
+     * Returns an existing result provider for a given query, if it was previously constructed, returns null otherwise.
+     * Will not construct and initialize new result providers.
+     */
+        public IQueryResultProvider peekExistingResultProvider(PQuery query);
+
+        /**
+         * Propagates all pending updates in this query backend. The implementation of this method is optional, and it 
+         * can be ignored entirely if the backend does not delay updates.   
+         * @since 1.6
+         */
+        public void flushUpdates();
+        
+        /**
+         * Disposes the query backend.
+         */
+        public abstract void dispose();
+        
+        /**
+         * @return the factory that created this backend, if this functionality is supported
+         * @since 2.1
+         */
+        public IQueryBackendFactory getFactory();
+
+}