We present a two-level model of distributed computation based on the actor model. This two-level model is the basis for developing a semantic framework that supports dynamic customizability and separation of concerns in designing and reasoning about components of open distributed systems (ODS). ODS evolve dynamically and components of ODS interact with an environment that is not under their control. In particular, we would like to be able to consider separately issues such as: functional behavior of a service; failure semantics and fault tolerance protocols; and resource management issues such as memory management, migration, load balancing, and scheduling. In this report we consider remote creation, migration, and reachability snapshot services: their specification at different levels of abstraction, and their composition.

In this paper we give an empirical evaluation of an object-oriented method which we applied to the modelling of a complex industrial information system. We describe our methodology consisting of different notations and guidelines. We also briefly show a CASE environment that we are developing for supporting our methodology. At last, we report our experiences gained during the modelling process.

We present a specification logic for dynamic object systems that combines modalities with connectives expressing distribution, hiding and signature extension. The logic is given a semantics in certain abstract process structures and its usefulness illustrated by some simple examples.

Data Type Specification, in combination with modal logics for formalizing the process of building systems from interconnected components. This combination of logical and categorical techniques has also been applied to parallel program design languages in the style of UNITY [14] and IP [41], providing semantics for modularization techniques based on the notion of superposition. This has resulted in the development of a programming design language called Community [33]. Two formalisms that provide explicit support for object systems and can reason about their rewriting logic specifications have been recently developed. One is a version of the modal -calculus proposed by Lechner [48, 49] for reasoning about object-oriented Maude specifications. Another is Denker's objectoriented distributed temporal logic DTL + [24, 22], that extends the DTL and D 1 distributed object temporal logics of Ehrich and Denker [30, 23, 29]. Lechner [48, 49] uses her version of the modal -calculus to identif...

Our general goal is to provide a semantic foundation for the specification of concurrent and distributed object systems. We use Troll, a formal object-oriented language, for system specification. It is now widely accepted that object classes are unsuitable modularisation units when it comes to dealing with very large systems. An intermediate concept between the system and the objects is needed for allowing reusability of specifications and providing a clearer system structure. Enriching Troll with a module concept forces us to develop new theoretical constructs ensuring an appropriate underpinning of the language. We propose a module logic Mdtl for specifying and reasoning about the dynamic aspects of distributed and modular object systems. The main features of the logic include the ability to express module interaction and internal module concurrency. In this paper, we present the syntax and model-theoretic semantics of the module logic Mdtl. The logic is illustrated and...

Tool support helps developers of information systems to considerably increase the accuracy and quality of its models. The use of formal languages in the conceptual modelling process allows the construction of powerful validation tools by executing the model. Executing a model is a very difficult task, when not impossible, due to the high level of abstraction in which it is described. In this paper we analyse some aspects to be taken into account when executing models specified with the formal object-oriented language Troll.

In this paper we present Mdtl, a distributed temporal logic for reasoning about both synchronously and asynchronously communicating modular object systems. Mdtl is an extension of Dtl reflecting besides communication and non-determinism also concurrency and supporting asynchronous communication. It is based on n-agent logics. Formulae written in Mdtl are interpreted over labelled prime event structures. A model construction for (a)synchronous concurrent composition has been provided in previous work. The model theory together with Mdtl allows a whole range of issues, like reasoning and verification.