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 C. 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. 2003 Elsevier B.V. All rights reserved.