David Scholefield

A specification-oriented semantics for the refinement of real-time systems

A refinement calculus for the development of real-time systems is presented. The calculus is based upon a wide-spectrum language called the temporal agent model (TAM), within which both functional and timing properties can be expressed in either abstract or concrete terms. A specification-oriented semantics for the language is given. Program development is considered as a refinement process, i.e. calculation of a structured program from an unstructured specification. A calculus of decomposition is defined. An example program is developed.

TAM: A Formal Framework for the Development of Distributed Real-Time Systems

The Temporal Agent Model (TAM) is a wide-spectrum development language for real-time systems. In TAM, limited resources are modelled by deriving release times and absolute deadlines from weakest pre-condition predicate transformers. In this paper the language syntax and semantics are described along with a number of examples.

Proving properties of real-time semaphores

Much work has been undertaken on investigating the use of semaphore primitives in concurrent programming languages. It has been shown that semaphores are adequate for expressing many forms of concurrency control, including the enforcement of communication protocols, and mutual exclusion protocols on shared resources. In this paper we present a formal language for real-time distributed programs which includes a semaphore primitive. This primitive is used to lock and unlock resources which are directly associated with either processors or communication channels. The semaphores are real-time, i.e. the programmer can express timing constraints about when the semaphores should lock and unlock. It is demonstrated that, using these semaphores, a number of apparently disjoint issues in real-time distributed systems theory can be unified within a single notion of resource restriction. In particular it is shown that different models of communication, control of shared access to resources (mutual exclusion), and process to processor mapping (physical placement), can all be expressed and reasoned about in a unified manner.

Real-time refinement in Manna and Pnueli's temporal logic

A refinement calculus for the development of real-time systems is presented. The calculus is based upon a wide-spectrum language called TAM (the Temporal Agent Model), within which both functional and timing properties can be expressed in either abstract or concrete terms. A specification oriented semantics is given for the language. Program development is considered as a refinement process i.e. thecalculation of a structured program from an unstructured specification. An example program is developed.

Weakest precondition semantics for time and concurrency

Abstract A weakest precondition semantics for a real-time concurrent language is defined. An example in verification is presented, and the use of predicate transformers as the basis of a refinement calculus is also discussed.

A Predicative Semantics for the Refinement of Real-Time Systems

A formal framework for a calculus of real-time systems is presented. Specifications and program statements are combined into a single language called TAM (the Temporal Agent Model), that allows the user to express both functional and timing properties. A specification-oriented semantics for TAM is given, along with the definition of a refinement relation and a calculus which is sound with respect to that relation. A simple real-time program is also developed using the calculus.

Transformational vs reactive refinement in real-time systems

Abstract Real-time software development is investigated in an extended form of the Z language, and compared with development in the Temporal Agent Model (TAM): a theory specifically designed for real-time systems. Both of these theories use refinement as the main development method, and by defining a translation between the extended Z language, and the TAM language, we are able to compare the two refinement relations in terms of an example real-time system refinement.

Compensation functions and requirements

It would be clearly difficult to try to use propositional logic alone a~ a language for specifying reactive systems. However, in most cases the unsuitability of a choice of language may not be so clear, for example~ is Timed CCS, [Tof89], useful for specifying safety-critical real-time systems ? With a taxonomy of requirements we would be able to ascertain the suitability of a language by trying to specify a sample requirement of each relevant class in the taxonomy. If one language was capable of expressing all relevant classes then it would justify that choice of language.

The refinement of real-time systems

The Temporal Agent Model (TAM) is a widespectrum development language for real-time systems. In TAM, limited resources are modelled by deriving release times and absolute deadlines from weakest precondition predicate transformers. The language syntax is described, a refinement calculus is presented and a number of examples are discussed. Our development method does not address issues such as schedulability and process allocation.