What are GraphDB local notifications

Notifications are a publish/subscribe mechanism for registering and receiving events from a GraphDB repository whenever triples matching a certain graph pattern are inserted or removed.

The RDF4J API provides such a mechanism where a RepositoryConnectionListener can be notified of changes to a NotifiyingRepositoryConnection. However, the GraphDB notifications API works at a lower level and uses the internal raw entity IDs for subject, predicate, and object instead of Java objects. The benefit of this is that a much higher performance is possible. The downside is that the client must do a separate lookup to get the actual entity values and because of this, the notification mechanism works only when the client is running inside the same JVM as the repository instance.


Local notifications only work in an embedded GraphDB instance, which is usually used only in test environments.

For remote notifications, we recommend using the Kafka GraphDB Connector.

How to register for local notifications

To receive notifications, register by providing a SPARQL query.


The SPARQL query is interpreted as a plain graph pattern by ignoring all more complicated SPARQL constructs such as FILTER, OPTIONAL, DISTINCT, LIMIT, ORDER BY, etc. Therefore, the SPARQL query is interpreted as a complex graph pattern involving triple patterns combined by means of joins and unions at any level. The order of the triple patterns is not significant.

Here is an example of how to register for notifications based on a given SPARQL query:

AbstractRepository rep =
EntityPool ent = ((OwlimSchemaRepository)owlimSail).getEntities();
String query = "SELECT * WHERE { ?s rdf:type ?o }";
SPARQLQueryListener listener =
    new SPARQLQueryListener(query, rep, ent) {
        public void notifyMatch(int subj, int pred, int obj, int context) {
            System.out.println("Notification on subject: " + subj);
rep.addListener(listener);    // start receiving notifications
rep.removeListener(listener); // stop receiving notifications

In the example code, the caller will be asynchronously notified about incoming statements matching the pattern ?s rdf:type ?o.


In general, notifications are sent for all incoming triples, which contribute to a solution of the query. The integer parameters in the notifyMatch method can be mapped to values using the EntityPool object. Furthermore, any statements inferred from newly inserted statements are also subject to handling by the notification mechanism, i.e., clients are notified also of new implicit statements when the requested triple pattern matches.


The subscriber should not rely on any particular order or distinctness of the statement notifications. Duplicate statements might be delivered in response to a graph pattern subscription in an order not even bound to the chronological order of the statements insertion in the underlying triplestore.


The purpose of the notification services is to enable the efficient and timely discovery of newly added RDF data. Therefore, it should be treated as a mechanism for giving the client a hint that certain new data is available and not as an asynchronous SPARQL evaluation engine.