user-defined properties: user can extend the set of applicable properties and add their own to specify their own requirements language annexes: the core language is enhanced by annex languages that enrich the architecture description. For now, the following annexes have been defined. Behavior annex: add components behavior with state machines Error-model annex: specifies fault and propagation concerns ARINC653 annex: defines modelling patterns for modelling avionics system Data-Model annex: describes the modelling of specific data constraint with AADL