Unlike previous behaviour models, reactive behaviour description oncludes not only what to execute but also when to excute it. programming languages, database systems and graphical user interfaces are being enhanced to provide explicit support for reactive behaviour due to the large range of application which naturally express their semantics using this paradigm. This paper presents a common framwork in which current alternatives to reactive behaviour support in object oriented systems can be placed and compared. This framwork imposes some classification festres, that suggest some new approaches for the reactive behaviour support.