Virtual Graphs

Intro

The Simantics database client allows for defining memory-based and disk-based graph fragments which are applied on top of the server-based semantic graph.

A reading user perceives the combined model and the virtual graph information can be specifically queried if necessary.

A modifying user needs to specify in which virtual graph the modifications are made.

Virtual graphs are manipulated via the following interfaces

• org.simantics.db.service.VirtualGraphSupport, for management
• org.simantics.db.request.WriteTraits, for identifying the graph to write into

Specification

A write request has a single graph into which it writes. This is determined by WriteTraits and usually as a parameter to WriteRequest. If null is provided, the client applies modifications into the persistent graph. The following rules apply

• New resources are created into the given virtual graph
• Claim statements are added into the given virtual graph
• Value changes are applied into the given virtual graph
• For denied statements the location of the statement is determined and the statement is removed from that virtual graph.

The user can perform modifications into multiple virtual graphs within a single transaction. This is accomplished by issuing a new synchronous modification (WriteGraph.sync) into a new virtual graph.

Examples

The following code examples show in practice how to write into virtual graphs, both memory- and disk-based. Writing to several virtual graphs within the same write transaction is also demonstrated.

<syntaxhighlight lang="java"> package org.simantics.db.tests.api.support.virtualGraphSupport;

import org.simantics.db.ReadGraph; import org.simantics.db.RequestProcessor; import org.simantics.db.Resource; import org.simantics.db.Session; import org.simantics.db.Statement; import org.simantics.db.VirtualGraph; import org.simantics.db.WriteGraph; import org.simantics.db.common.request.ReadRequest; import org.simantics.db.common.request.WriteRequest; import org.simantics.db.common.request.WriteResultRequest; import org.simantics.db.common.utils.NameUtils; import org.simantics.db.exception.DatabaseException; import org.simantics.db.service.VirtualGraphSupport; import org.simantics.layer0.Layer0;

public class VirtualGraphExample {

   public Resource createLibrary(RequestProcessor processor, VirtualGraph vg, final String libraryName)
           throws DatabaseException {
       return processor.syncRequest(new WriteResultRequest<Resource>(vg) {
           @Override
           public Resource perform(WriteGraph graph) throws DatabaseException {
               Layer0 L0 = Layer0.getInstance(graph);
               Resource r = graph.newResource();
               graph.claim(r, L0.InstanceOf, null, L0.Library);
               graph.claimLiteral(r, L0.HasName, libraryName);
               return r;
           }
       });
   }

   public void testVirtualGraphs(Session session) throws DatabaseException {
       VirtualGraphSupport vgSupport = session.getService(VirtualGraphSupport.class);
       VirtualGraph memory = vgSupport.getMemoryPersistent("memory");
       VirtualGraph workspace = vgSupport.getWorkspacePersistent("workspace");
       // NOTICE: resource are created in difference virtual graphs in separate
       // transactions through Session.syncRequest.
       Resource memResource = createLibrary(session, memory, "memory");
       Resource workspaceResource = createLibrary(session, workspace, "workspace");
       printVirtualGraphs(session);
   }

   public void testMultipleVirtualGraphsInSameTransaction(Session session) throws DatabaseException {
       final VirtualGraphSupport vgSupport = session.getService(VirtualGraphSupport.class);
       session.syncRequest(new WriteRequest() {
           @Override
           public void perform(WriteGraph graph) throws DatabaseException {
               VirtualGraph memory = vgSupport.getMemoryPersistent("memory");
               VirtualGraph workspace = vgSupport.getWorkspacePersistent("workspace");
               // NOTICE: resource are created in different virtual graphs in
               // the same transaction through WriteGraph.syncRequest
               Resource memResource = createLibrary(graph, memory, "memory");
               Resource workspaceResource = createLibrary(graph, workspace, "workspace");
           }
       });
       printVirtualGraphs(session);
   }

   public void printVirtualGraphs(Session session) throws DatabaseException {
       session.syncRequest(new ReadRequest() {
           @Override
           public void run(ReadGraph graph) throws DatabaseException {
               VirtualGraphSupport vgSupport = graph.getService(VirtualGraphSupport.class);
               for (VirtualGraph vg : vgSupport.listGraphs()) {
                   for (Statement stm : vgSupport.listStatements(vg)) {
                       System.out.println("Statement: " + NameUtils.toString(graph, stm));
                   }
                   for (Resource r : vgSupport.listValues(vg)) {
                       System.out.println("Literal value: " + graph.getValue(r));
                   }
               }
           }
       });
   }

} </syntaxhighlight>