We have developed an ontology based framework that evaluates compatibility between processing modules within an end user development framework, using MIT Lincoln Laboratory's Composable Analytics environment as a test case. In particular, we focus on inter-module semantic compatibility as well as compatibility between data and modules. Our framework includes a core ontology that provides an extendible vocabulary that can describe module attributes, module input and output requirements and preferences, and data characteristics that are pertinent to selecting appropriate modules in a given situation. Based on the ontological description of the modules and data, we first present a framework that takes a rule based approach in measuring semantic compatibility. Later, we extend the rule based approach to a flexible fuzzy logic based semantic compatibility evaluator. We have built an initial simulator to test module compatibility under varying situations. The simulator takes in the ontological description of the modules and data and calculates semantic compatibility. We believe the framework and simulation environment together will help both the developers test new modules they create as well as support end users in composing new capabilities. In this paper, we describe the details of the framework, the simulation environment, and our iterative process in developing the module ontology.