Abstract State Machines 1988-1998: Commented ASM Bibliography

An annotated bibliography of papers which deal with or use Abstract State Machines (ASMs), as of January 1998.Comment: Also maintained as a BibTeX file at http://www.eecs.umich.edu/gasm

Contexts, refinement and determinism

In this paper we have been influenced by those who take an “engineering view” of the problem of designing systems, i.e. a view that is motivated by what someone designing a real system will be concerned with, and what questions will arise as they work on their design. Specifically, we have borrowed from the testing work of Hennessy, de Nicola and van Glabbeek, e.g. [13, 5, 21, 40, 39]. Here we concentrate on one fundamental part of the engineering view and where consideration of it leads. The aspects we are concerned with are computational entities in contexts, observed by users. This leads to formalising design steps that are often left informal, and that in turn gives insights into non-determinism and ultimately leads to being able to use refinement in situations where existing techniques fail

Simulation Techniques

In the papers surveyed in this thesis a number of simulation techniques are presented together with their applications to several examples. The papers improve upon existing techniques and introduce new techniques. The improvement of existing techniques is motivated in programming methodology: It is demonstrated that existing techniques often introduce a double proof burden whereas the improved techniques alleviate such a burden. One application is to ensure delay insensitivity in a class of self-timed circuits. A major part of the thesis is concerned with the deduction and use of two simulation techniques to prove the correctness of translations from subsets of occam-2 to transputer code

Towards An Automated Approach to Hardware/Software Decomposition

We propose in this paper an algebraic approach to hard-ware/software partitioning in Verilog Hardware Description Language (HDL). We explore a collection of algebraic laws for Verilog programs, from which we design a set of syntax-based algebraic rules to conduct hardware/software partitioning. The co-specification language and the target hardware and software description languages are specific subsets of Verilog. Through this, we confirm successful verification for the correctness of the partitioning process by an algebra of Verilog. Facilitated by Verilog’s rich features, we have also successfully studied hw/sw partitioning for environment-driven systems.Singapore-MIT Alliance (SMA

Flexible refinement

To help make refinement more usable in practice we introduce a general, flexible model of refinement. This is defined in terms of what contexts an entity can appear in, and what observations can be made of it in those contexts. Our general model is expressed in terms of an operational semantics, and by exploiting the well-known isomorphism between state-based relational semantics and event-based labelled transition semantics we were able to take particular models from both the state- and event-based literature, reflect on them and gradually evolve our general model. We are also able to view our general model both as a testing semantics and as a logical theory with refinement as implication. Our general model can used as a bridge between different particular special models and using this bridge we compare the definition of determinism found in different special models. We do this because the reduction of nondeterminism underpins many definitions of refinement found in a variety of special models. To our surprise we find that the definition of determinism commonly used in the process algebra literature to be at odds with determinism as defined in other special models. In order to rectify this situation we return to the intuitions expressed by Milner in CCS and by formalising these intuitions we are able to define determinism in process algebra in such a way that it no longer at odds with the definitions we have taken from other special models. Using our abstract definition of determinism we are able to construct a new model, interactive branching programs, that is an implementable subset of process algebra. Later in the chapter we show explicitly how five special models, taken from the literature, are instances of our general model. This is done simply by fixing the sets of contexts and observations involved. Next we define vertical refinement on our general model. Vertical refinement can be seen both as a generalisation of what, in the literature, has been called action refinement or non-atomic refinement. Alternatively, by viewing a layer as a logical theory, vertical refinement is a theory morphism, formalised as a Galois connection. By constructing a vertical refinement between broadcast processes and interactive branching programs we can see how interactive branching programs can be implemented on a platform providing broadcast communication. But we have been unable to extend this theory morphism to implement all of process algebra using broadcast communication. Upon investigation we show the problem arises with the examples that caused the problem with the definition of determinism on process algebra. Finally we illustrate the usefulness of our flexible general model by formally developing a single entity that contains events that use handshake communication and events that use broadcast communication

Formal semantics for LIPS (Language for Implementing Parallel/distributed Systems)

This thesis presents operational semantics and an abstract machine for a point-to-point asynchronous message passing language called LIPS (Language for Implementing Parallel/ distributed Systems). One of the distinctive features of LIPS is its capability to handle computation and communication independently. Taking advantage of this capability, a two steps strategy has been adopted to define the operational semantics. The two steps are as follows: • A big-step semantics with single-step re-writes is used to relate the expressions and their evaluated results (computational part of LIPS). • The developed big-step semantics has been extended with Structural Operational Semantics (SOS) to describe the asynchronous message passing of LIPS (communication part of LIPS). The communication in LIPS has been implemented using Asynchronous Message Passing System (AMPS). It makes use of very simple data structures and avoids the use of buffers. While operational semantics is used to specify the meaning of programs, abstract machines are used to provide intermediate representation of the language's implementation. LIPS Abstract Machine (LAM) is defined to execute LIPS programs. The correctness of the execution of the LIPS program/expression written using the operational semantics is verified by comparing it with its equivalent code generated using the abstract machine. Specification of Asynchronous Communicating Systems (SACS) is a process algebra developed to specify the communication in LIPS programs. It is an asynchronous variant of Synchronous Calculus of Communicating Systems (SCCS). This research presents the SOS for SACS and looks at the bisimulation equivalence properties for SACS which can be used to verify the behaviour of a specified process. An implementation is said to be complete when it is equivalent to its specifications. SACS has been used for the high level specification of the communication part of LIPS programs and is implemented using AMPS. This research proves that SACS and AMPS are equivalent by defining a weak bisimulation equivalence relation between the SOS of both SACS and AMPS