James F Peters

Proving specifications of tasking systems using Ada/TL

ADA/TL is a language for specification of the behavior of systems of communicating tasks. It merges concepts of the specification part of ADA, VDM specification of packages, and temporal logic specification of task behavior. The TL part consists of constructive specification of behaviors of individual tasks and a system specification of the properties of the interaction of tasks. A proof of a system specification consists of showing that the system property holds over all possible interleavings of the task behaviors. This paper extends earlier work on proof of system specifications to cover more general branching behaviors of individual tasks, including cases of timed task calls and timed rendezvous. The constructive specification of each individual task defines a finite state computation model of its possible behaviors with allowed communication between task computations. The proof system uses marker symbols to represent the current state within each task computation, inference rules to justify transformations from one state to the next, and a proof tableau for representing the proof steps. The method rests upon the technique of using an invariant system property to identify a finite computation model of the interaction of all the system tasks. The proof tableau symbolically traces threads of control in all branches of the finite state model of the interaction of all of the system tasks. The proof method is illustrated herein using an example of a traffic walk-light controller with a timed behavior.

Designing a dynamic integrity constraint checker with nonmonotonic logic

The authors report on the design of a dynamic integrity constraint checker with a nonmonotonic interval logic (IL). Central to this logic is the inclusion of the unless operator which captures the nonmonotonicity of dynamic integrity constraints over temporal intervals. IL is embedded in the Ada/ISL Interval Specification Language which has been utilized in the design of the Icarus Integrity System. In this system, the answer to a query depends on the availability of an explicit body of knowledge (knowledge base) about the integrity of data items contained in the query. The principal inference mechanism in this system is the refutation of faulty beliefs about data based on partial information and intuition, with respect to facts in the knowledge base. A technique for the verification of the Icarus kernel is presented. A family of assertions about the completeness, correctness, and confidence integrity characteristics about data is included in the integrity model.<<ETX>>

WHAT DOES IT MEAN TO BE " THE SAME " ? A BIOLOGICAL VARIANT OF THE BORSUK-ULAM THEOREM

A unifying principle underlies the organization of physical and biological systems. It relates to a well-known topological theorem which succinctly states that an activity on a planar circumference projects to two activities with “matching description” into a sphere. Here we ask: What does “matching description” mean? Has it something to do with “identity”? Going through different formulations of the principle of identity, we describe diverse possible meanings of the term “matching description”. We demonstrate that the concepts of “sameness”, “equality”, “belonging together” stand for intertwined levels with mutual interactions. By showing that “matching” description is a very general and malleable concept, we provide a novel testable approach to “identity” that yields helpful insights into physical and biological matters. Indeed, we illustrate how a novel mathematical approach derived from the Borsuk-Ulam theorem, termed bio-BUT, might explain the astonishing biological “multiplicity from identity” of evolving living beings as well as the logic of their intricate biochemical arrangements.

Temporal specification of an integrity kernel for multimedia office systems

The authors report on the temporal specification of integrity systems with the interval specification language ISL. ISL is based on a form of interval temporal logic and provides a framework for a logic of knowledge and belief about data integrity. ISL is a design tool for integrity kernels in office information systems where the dynamic evaluation of data integrity based upon partial knowledge and informed judgment is required. The D.D. Clark and D.R.A. Wilson (1981) integrity model, designed to prevent fraudulent and erroneous data modification, is subsumed. An integrity system which includes extensions to the concept defined in the Multimedia Office Server (MULTOS) project is given. An integrity characteristic tuple incorporating the notions of correctness, completeness, quality, timeliness, and confidence associated with each constrained document component is presented. A specification for a simplified integrity kernel is provided.<<ETX>>

CONDUCTOR: a model for reliable interprocess communication

The authors introduce a model for reliable interprocess communication based on an extension of the gentleman administrator model. The architecture of the CONDUCTOR model provides increased concurrency and a simplified user view of a distributed system. The increased concurrency stems from the potential for multiple instances of administrators to coexist within administrator groups. Users communicate directly with a conductor process instead of a variety of administrators. The new model provides an abstraction which hides administrators needed to service user requests. This form of multiprocess structuring is in keeping with the philosophy of the original Thoth system. A basis for reliable communication between administrator groups and the conductor process is presented. Reliable communication in this model is provided by enforcing atomicity of message delivery and ordering of messages. The architecture of the CONDUCTOR model is robust inasmuch as it is process failure tolerant. A mechanism for detecting and replacing failed administrators of a failed conductor using N. Natarjans (1988) watchdog processes is presented.<<ETX>>

Logic of knowledge and belief in the design of an integrity kernel for an office information system (abstract)

An integrity specification language (ISL) based upon a form of interval temporal logic is defined and the framework for a logic of knowledge and beliefs about data integrity is developed. The intended purpose of ISL is for the design of integrity kernels in an office information system in which the dynamic evaluation of data integrity based upon partial knowledge and informed judgement relative to update request by clients, is required. ISL itself is described in an earlier paper and summarized in this paper. Beliefs in ISL are specified with a form of interval temporal logic and provide an extension of the Moser technique for formulating beliefs. The Clark and Wilson model designed to prevent fraudulent and erroneous data modification is subsumed. An integrity Characteristic Tuple (ICT) incorporates the notions of correctness, completeness, quality, timeliness and confidence is associated with each Constrained Data Item (CDI). An integrity system which includes extensions of the concept and function of the server architecture as defined in the Multimedia Office Server (MULTOS) project, is given. An integrity kernel is defined which incorporates an algorithm for the detection of faults in presumptions about data integrity based upon knowledge and beliefs. A simplified integrity kernel is specified formally and a corresponding sample server-client session is provided.