In this paper we use the idea of conceptual space introduced by Boden and redefine some properties such appropriateness and relevance that facilitate the computational implementation of the transformational creativity mechanism. While appropriateness can only be evaluated by an expert, relevance can be objectively measured for any spectator. Computational creativity is based on the relationship between appropriateness and relevance of a concept, and therefore a computational system can be used to support this task. The paper analyses this relationship in the field of music in order to obtain a computer tool to support the musical composition task.