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P9502   J.A. Bergstra & P. Klint
        "The discrete time ToolBus"


Building large, heterogeneous, distributed software systems poses
serious problems for the software engineer; achieving interoperability
of software systems is still a major challenge.

In a previous paper, we have proposed to get control over the possible
interactions between software components (``tools'') by forbidding
direct inter-tool communication.  Instead, all interactions are
controlled by a process-oriented ``script'' that formalizes all the
desired interactions among tools.  This leads to a component
interconnection architecture resembling a hardware communication bus,
and therefore we call it a ``ToolBus''.

Based on the experience with our previous proposal, we extend ToolBus
scripts with features like conditionals and simple operations on the
built-in data type of terms. More significantly, we introduce discrete
time and give detailed descriptions of the protocol between ToolBus
and tools. As a result, we can completely define the dynamic
connection and disconnection of tools as well as notions like
``monitoring'' the execution of the ToolBus and ``dynamic
reconfiguration'' of the ToolBus during execution.

These extensions are defined in a generic framework intended for the
experimentation with new ToolBus features.


1991 CR Categories:
C.2.4 [Computer-communication networks]: Distributed systems;
D.2.1 [Software Engineering]: Requirements/Specifications;
D.2.2 [Software Engineering]: Tools and techniques;
D.2.6 [Software Engineering]: Programming Environments;
D.3.4 [Programming Languages]: Processors;
D.4.1 [Operating Systems]: Process management;
D.4.4 [Operating Systems]: Communications management;
H.5.2 [Information interfaces and presentation]: User interfaces.

1991 Mathematics Subject Classification:
68N15 [Software]: Programming Languages;
68N20 [Software]: Compilers and generators;
68Q65 [Theory of computing]:  Abstract data types; algebraic specification.

Key Words & Phrases: interoperability of software tools, modularity,
control integration, client/server architectures, distributed systems,
process interpreter, prototyping, software development methodology,
randomized execution.