EPOS provides event stream processing components using a powerful and extensible encoding/decoding architecture.

The 52°North Sensor Event Service established the use of event streams for complex event processing. While the architecture showed its potential, additional use cases appeared where the specific SES interface was a significant overhead. This project narrows the event pattern components developed within the SES down to its core functionality and allows its inclusion into other software. In particular, it can help to enable Publish/Subscribe functionality for data provisioning web services.

The current development snapshot of the SES uses this components and will include it in prior releases, starting with version 1.3.0.

The stream processing and pattern matching features are heavily based on Esper.

EPOS provides two interfaces which allow easy extension of the framework

• org.n52.epos.transform.EposTransformer
• org.n52.epos.filter.FilterInstantiationRepository

The EposTransformer interface provides methods for transformation of every kind of input into an EposEvent instance. A realization shall determine at runtime if it supports the given input by returning a boolean for the supportsInput(Object input) method. If true, the EposEvent transform(Object input) is called in which the realization processes the given object.

The FilterInstantiationRepository can be used to implement additional filters. There are two basic types of filters which are then combined as a Rule:

• org.n52.epos.filter.ActiveFilter
• org.n52.epos.filter.PassiveFilter

A realization of FilterInstantiationRepository can be considered as a transformer of a Filter representation (e.g. an XPath configuration) into the internal EposFilter instance. An example is the org.n52.epos.engine.filter.XPathFilterRepository.

Implementations of the above described interfaces need to be exposed via Java's ServiceLoader pattern (META-INF/services/"interface-as-filename", e.g. see this example).

mvn clean install does the basic job. This includes integration-level tests to ensure the stable behavior of the stream processing.

EPOS has no special meaning or is an abbreviation. If desperately required, one could use "Event Processing Open-closed Suite" as the complete project name.