Gradoop Store API

The Store API offers a way to define predicates at the DataSources of the supported Store instances. The predicates, containing id, label and property filters, will be executed directly at the distributed store system which results in a smaller amount of data transferred to Gradoop. In this chapter providing predicates for the HBaseDataSource will be explained as usage example. Obviously, they can be adapted to other stores.

A DataSource which implements the FilterableDataSource interface, offers functions to apply predicates for all three the graph elements Vertex, Edge and GraphHead of the EPGM. Each returns a copy of the DataSource instance including the applied filter. The available functions are:

• source.applyVertexPredicate(ElementQuery)
• source.applyEdgePredicate(ElementQuery)
• source.applyGraphPredicate(ElementQuery)

Each function requires a ElementQuery as parameter which represents the unity of all element predicates. An instance can be created through the Query helper class:

Query.elements().fromAll()                          .where(ElementFilter)
                .fromSets(GradoopIdSet gradoopIds)  .noFilter()
                .fromSets(GradoopId... gradoopIds)

An ElementFilter can be a single filter instance or a logical combination of them. The following filters are available:

Signature	Description
LabelIn(String... labels)	Returns graph elements whose labels are equal to the defined ones.
LabelReg(Pattern reg)	Returns graph elements whose labels match with the given regular expression.
PropEquals(String key, Object value)	Returns graph elements that have a property with the given name and value.
PropReg(String key, Pattern reg)	Returns graph elements that have a property with the given name and a value that matches the given regular expression.
PropLargerThan(String key, Object min, boolean include)	Returns graph elements that have a property with the given name and a numeric value that is larger than the given min value. If the include flag is set to true, elements with values that are equal to min will be included to the result set.

Example usage

DataSource dataSource = new HBaseDataSource(store, config);

dataSource = dataSource.applyEdgePredicate(
  // fromAll() => No ID filter
  Query.elements().fromAll() 
    // WHERE edge.label LIKE '^has.*$' OR edge.since < 2015
    .where(HBaseFilters.<Edge>labelReg(Pattern.compile("^has.*"))
      .or(HBaseFilters.<Edge>propLargerThan("since", 2015, true).negate())));

dataSource = dataSource.applyVertexPredicate(
  // fromAll() => No ID filter
  Query.elements().fromAll()
    // WHERE vertex.label = 'Person' AND
    //       (vertex.name = 'Meier' OR vertex.name = 'Mueller')
    .where(HBaseFilters.<Vertex>labelIn("Person")
      .and(HBaseFilters.<Vertex>propEquals("name", "Meier")
        .or(HBaseFilters.<Vertex>propEquals("name", "Mueller"));

LogicalGraph g = dataSource.getLogicalGraph();