The expressive performance of music demands creativity in at least two ways. First of all, the task of the performer is underspecified, even if the music is performed from a score. The performer has to limit the scope of possibilities to come to a unitary performance. Secondly, an important aspect of a performance is to deviate from strict regularity; only through deviation does a meaningful performance arise. Most models of expressive music performance have focused on this second type of creativity. Less attention has been paid to the process of constraining performance space. In this presentation, I will present some existing models of expressivity as deviation. I will add to that an investigation of the dimensions of performance space.