Formal specifications are difficult to read.Executable specifications allow to see the behavior of the specified objects and help the domain specialist to detect errors quickly. We present here a method which allows to write axiomatic specifications which can be executed and discuss the limitations in expressive power imposed by the restriction to constructive axioms and how it can be circumvented. The method results from practical efforts to formalize the meaning of object types for Geographic Information Systems. If such data are shared betweenorganisations, differences in the semantics become apparent and formal methods for their definition become necessary. Most formal methods are based on first order languages. Software engineering often uses algebraic methods, but tools practically used for data exchange standard definitions are restricted to signatures and do not capture the behavior of the operations. We present here an algebraic approach using a functional programming language...

Abstract. The concept of niche (setting, context, habitat, environment) has been little studied by ontologists, in spite of its wide application in a variety of disciplines from evolutionary biology to economics. What follows is a first formal theory of this concept, a theory of the relations between objects and their niches. The theory builds upon existing work on mereology, topology, and the theory of spatial location as tools of formal ontology. It will be illustrated above all by means of simple biological examples, but the concept of niche should be understood as being, like concepts such as part, boundary, and location, a structural concept that is applicable in principle to a wide range of different domains.