The concept of event is used in a lot of meanings. It can be the possible outcome of doing something (probability theory), it can be a business transaction (accounting), or just a plain happening. In software engineering, the concept of event is also used a lot. It is used to accomplish loose coupling between software components or to realise interaction between different services. There is
however not a consensus on the meaning of `an event'. In enterprise ontologies, an event is defined
as a happening at one point in time, or as an activity which takes time to complete. In requirement engineering, the same different uses can be found, together with an event as a request for something that needs to be done. These differences can also be found in implementation. All these distinct purposes of the word event make it difficult to integrate and use different requirement engineering
techniques. Comparison or transformations between models drawn in different grammars is impossible because of the ambiguity of the concept of event. We define three meanings for an event that are used by enterprise ontologies and requirement engineering techniques: an achievement
(happening at one point in time), an activity (happening over time) and a request (a demand for something that needs to be done). We also identify a missing link between real economic events, the events defined in the requirements model and the events used in implementation.