Publish/Subscribe Context Broker – Orion

What it is

The Orion Context Broker is an implementation of the Publish/Subscribe Context Broker GE, providing the NGSI9 and NGSI10 interfaces. Using these interfaces, clients can do several operations:

Why get it

If you are developing a Data/Context scenario, a broker like the Orion Context Broker is a must. You would need a component in the architecture able to mediate between consumer producers (e.g. sensors) and the context consumer applications (e.g. an smartphone applications taking advantage of the context information provided by the sensors). The Orion Context Broker fulfils this functionality in your architecture.

Avaliable for:


Basic Actors in the Publish/Subscribe Context Broker GE Model

Publish/Subscribe Context Broker

As already mentioned the Publish/Subscribe Context Broker (CB) is the main component of the architecture. It works as a handler and aggregator of context data and as an interface between architecture actors. Primarily the CB has to control context flow among all attached actors; in order to do that, the CB has to know every Context Provider (CP) in the architecture; this feature is done through an announcement process detailed in the next sections.

Typically, the CB provides a Context Provider Lookup Service and a Context Persistence Service.

Context Producer

A Context Producer (CP) is an actor able to generate context. The basic Context Producer is the one that spontaneously updates context information, about one or more context attributes according to its internal logic. This comunication is between CS and CB is in push mode, from the CP to the CB.

Context Producers can work also in pull base way, in which case they are referred as Context Providers.

Context Provider

A Context Provider (CPr) is an specialized kind of Context Producer actor, which provides context information on demand, in synchronous mode; that means that the Publish/Subscribe Context Broker or even the Context Consumer can invoke the CP in order to acquire context information. A CP provides context data only further to a specific invocation. Moreover, a CP can produce new context information inferred from the computation of input parameters; hence it is many times responsible for reasoning on high-level context information and for sensor data fusion. Every CP registers its availability and capabilities by sending appropriate announcements to the CB and exposes interfaces to provide context information to the CB and to Context Consumers.

Context Consumer

A Context Consumer (CC) is an entity (e.g. a context based application) that exploits context information. A CC can retrieve context information sending a request to the CB or invoking directly a CP over a specific interface. Another way for the CC to obtain information is by subscribing to context information updates that match certain conditions (e.g., are related to certain set of entities). The CC registers a call-back operation with the subscription for the purpose, so the CB notifies the CC about relevant updates on the context by invoking this call-back function.

Finally, some kind of Context Consumer may expose update context operations to be invoked by CB. This is mainly related with actuation capabilities, i.e. the update at Context Consumer produces a given actuation, e.g. turn on/off a lamp.


Every exchange of context data here is referred to a specific entity, which can be in its order a complex group of more than one entity. An entity is the subject (e.g. user or group of users, things or group of things, etc.), which context data refer to. It is composed of two parts: a type and an identifier. Every Context Provider supports one or more entity types and this information is published to the Publish/Subscribe Context Broker during an announcement process described later.

A type is an object that categorizes a set of entities; for example entity types are:



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