CoMex (Coordination Mechanism) is a system to coordinate the execution of tasks accessing coordinable entities. It uses coordination rules to describe the temporal and logical order of tasks performed in a cooperative work setting. These rules coordinate semantic dependencies between work activities carried out by different users. The coordination rules are implemented in a relational database. This makes CoMex unique and easy to integrate into an existing application. By illustrating a case from a real work setting we show how these rules can be created, which methodology can be applied for their production and how CoMex can be used in a web application. We also describe the implementation of CoMex and its architecture.