We developed a theory in order to address crucial questions of program design methodology. This theory deals with data locality which is a main issue in parallel programming. In this article, we regard this theory and its model as a minimum semantic domain for data parallel languages. The introduction of a semantic domain is justified because the classical data parallel languages (HPF and C*) have different intuitive semantics: Indeed, they use different concepts in order to express data locality. These concepts are alignment in HPF and shape in CH . Consequently these two languages define their own balance between compiler and programmer investments in order to reach program efficiency. We present our theory as a foundation for defining a better balance.