5.4.3 Using an Element Filter Callback for Subgraph Extraction

Oracle Spatial and Graph provides support for an easy subgraph extraction using user-defined element filter callbacks. An element filter callback defines a set of conditions that a vertex (or an edge) must meet in order to keep it in the subgraph. Users can define their own element filtering by implementing the VertexFilterCallback and EdgeFilterCallback API interfaces.

The following code fragment implements a VertexFilterCallback that validates if a vertex does not have a political role and its origin is the United States.

/**
* VertexFilterCallback to retrieve a vertex from the United States 
* that does not have a political role 
*/
private static class NonPoliticianFilterCallback 
implements VertexFilterCallback
{
@Override
public boolean keepVertex(OracleVertexBase vertex) 
{
String country = vertex.getProperty("country");
String role = vertex.getProperty("role");

if (country != null && country.equals("United States")) {
if (role == null || !role.toLowerCase().contains("political")) {
return true;
}
}

return false;
}

public static NonPoliticianFilterCallback getInstance()
{
return new NonPoliticianFilterCallback();
}
}

The following code fragment implements an EdgeFilterCallback that uses the VertexFilterCallback to keep only edges connected to the given input vertex, and whose connections are not politicians and come from the United States.

/**
 * EdgeFilterCallback to retrieve all edges connected to an input 
 * vertex with "collaborates" label, and whose vertex is from the 
 * United States with a role different than political
*/
private static class CollaboratorsFilterCallback 
implements EdgeFilterCallback
{
private VertexFilterCallback m_vfc;
private Vertex m_startV;

public CollaboratorsFilterCallback(VertexFilterCallback vfc, 
 Vertex v) 
{
m_vfc = vfc;
m_startV = v; 
}

@Override
public boolean keepEdge(OracleEdgeBase edge) 
{
if ("collaborates".equals(edge.getLabel())) {
if (edge.getVertex(Direction.IN).equals(m_startV) && 
m_vfc.keepVertex((OracleVertex) 
edge.getVertex(Direction.OUT))) {
return true;
}
else if (edge.getVertex(Direction.OUT).equals(m_startV) && 
 m_vfc.keepVertex((OracleVertex) 
edge.getVertex(Direction.IN))) {
return true;
}
}

return false;
}

public static CollaboratorsFilterCallback
getInstance(VertexFilterCallback vfc, Vertex v)
{
return new CollaboratorsFilterCallback(vfc, v);
}

}

Using the filter callbacks previously defined, the following code fragment loads a property graph, creates an instance of the filter callbacks and later gets all of Robert Smith’s collaborators who are not politicians and come from the United States.

OraclePropertyGraph opg = OraclePropertyGraph.getInstance(
 args, szGraphName);

// Clear existing vertices/edges in the property graph 
opg.clearRepository(); 

String szOPVFile = "../../data/connections.opv";
String szOPEFile = "../../data/connections.ope";

// This object will handle parallel data loading
OraclePropertyGraphDataLoader opgdl = OraclePropertyGraphDataLoader.getInstance();
opgdl.loadData(opg, szOPVFile, szOPEFile, dop); 

// VertexFilterCallback to retrieve all people from the United States // who are not politicians
NonPoliticianFilterCallback npvfc = NonPoliticianFilterCallback.getInstance();

// Initial vertex: Robert Smith
Vertex v = opg.getVertices("name", "Robert Smith").iterator().next();

// EdgeFilterCallback to retrieve all collaborators of Robert Smith 
// from the United States who are not politicians
CollaboratorsFilterCallback cefc = CollaboratorsFilterCallback.getInstance(npvfc, v);

Iterable<<Edge> smithCollabs = opg.getEdges((String[])null /* Match any 
of the properties */,
cefc /* Match the 
EdgeFilterCallback */
);
Iterator<<Edge> iter = smithCollabs.iterator();

System.out.println("\n\n--------Collaborators of Robert Smith from " +
 " the US and non-politician\n\n");
long countV = 0;
while (iter.hasNext()) {
Edge edge = iter.next(); // get the edge
// check if smith is the IN vertex
if (edge.getVertex(Direction.IN).equals(v)) {
 System.out.println(edge.getVertex(Direction.OUT) + "(Edge ID: " + 
 edge.getId() + ")"); // get out vertex
}
else {
System.out.println(edge.getVertex(Direction.IN)+ "(Edge ID: " + 
 edge.getId() + ")"); // get in vertex
}

countV++;
}

By default, all reading operations such as get all vertices, get all edges (and parallel approaches) will use the filter callbacks associated with the property graph using the methods opg.setVertexFilterCallback(vfc) and opg.setEdgeFilterCallback(efc). If there is no filter callback set, then all the vertices (or edges) and edges will be retrieved.

The following code fragment uses the default edge filter callback set on the property graph to retrieve the edges.

// VertexFilterCallback to retrieve all people from the United States // who are not politicians
NonPoliticianFilterCallback npvfc = NonPoliticianFilterCallback.getInstance();

// Initial vertex: Robert Smith
Vertex v = opg.getVertices("name", "Robert Smith").iterator().next();

// EdgeFilterCallback to retrieve all collaborators of Robert Smith 
// from the United States who are not politicians
CollaboratorsFilterCallback cefc = CollaboratorsFilterCallback.getInstance(npvfc, v);

opg.setEdgeFilterCallback(cefc);

Iterable<Edge> smithCollabs = opg.getEdges();
Iterator<Edge> iter = smithCollabs.iterator();

System.out.println("\n\n--------Collaborators of Robert Smith from " +
 " the US and non-politician\n\n");
long countV = 0;
while (iter.hasNext()) {
Edge edge = iter.next(); // get the edge
// check if smith is the IN vertex
if (edge.getVertex(Direction.IN).equals(v)) {
 System.out.println(edge.getVertex(Direction.OUT) + "(Edge ID: " + 
 edge.getId() + ")"); // get out vertex
}
else {
System.out.println(edge.getVertex(Direction.IN)+ "(Edge ID: " + 
 edge.getId() + ")"); // get in vertex
}

countV++;
}