Process Algebraic Specifications Research Articles

Specification Diagrams for Actor Systems

Traditional approaches to specifying distributed systems include temporal logic specification (e.g. TLA), and process algebra specification (e.g. LOTOS). We propose here a new form of graphical notation for specifying open distributed object systems. The primary design goal is to make a form of notation for defining message-passing behavior that is expressive, intuitively understandable, and that has a formal underlying semantics. We describe the language and its use through presentation of a series of example specifications. We also give an operationally-based interaction path semantics for specification diagrams.

LANGUAGE FEATURES FOR COOPERATION IN AN OBJECT-ORIENTED DATABASE ENVIRONMENT

We introduce the language LOTOS/TM for the formal specification of a network of cooperating agents with a shared data repository and private local data. LOTOS/TM is the orthogonal integration of the process-algebraic protocol specification language LOTOS and the functional, object-oriented database specification language TM. The specified world consists of a number of interacting LOTOS processes — describing the cooperating agents — and a special LOTOS process representing the shared data repository, which is modeled as a TM database. The data repository's functionality is made available to the other, cooperating processes through one or more external database gates. Interaction at such a gate corresponds to a method invocation in the database. In addition to shared persistent data, the TM language is used to specify the data encapsulated locally within processes, and the transient data communicated over gates. Some features of LOTOS/TM are inherently suitable for describing cooperation, such as combinators for synchronization on specific methods. These features are illustrated by examples showing navigation events on a shared graph structure that resembles a hypertext. Emphasis in the examples is placed on coordination aspects of the scenario. LOTOS/TM serves as a formalism for a more user-friendly specification language by the name of CoCoA that is currently under construction.