With orchestrations, one service may be realized through the cooperation of several services. This cooperation has to be formally described. In this paper, we propose to describe service orchestrations according to UML2 meta- model through three UML2 diagrams. Component dia- grams describe each service external interfaces. Collabo- ration diagrams describe the structural composition of ser- vices. And activity diagrams describe the orchestration of services. The main contribution of this article is to mix the orches- tration and composition meta-model with a context meta- model. Thus, we propose to include the descriptions of context awareness into the orchestration and composition meta-model. This approach allows application designers to describe flexible orchestration of services. Furthermore, describing compositions and their context-awareness with a model (conform to a meta-model) allows middleware with model-transformation capabilities to produce ad-hoc com- positions in term of adaptation to current context execution and in term of target execution platforms. We present in this article two kinds of adaptation of con- text aware orchestrations: deployment time and run time adaptations.