Esper is a platform for the analysis of real-time data, which may or may not be combined with historic data. Processing is developed using EPL (event processing language), which is based on SQL but has extensions to support pattern (and rules-based) matching. There is, however, a presumption that this is based on patterns developed using EPL as opposed to those that may have been developed in a third-party tool and then imported. While the product is available as an open source product for end users, OEMs require a commercial license. Several well-known stream processing products have Esper under their covers.
This paper has been superseded by EsperTech (2021) (December, 2021)