Showing papers by "Joost-Pieter Katoen published in 1997"

The Bounded Retransmission Protocol Must Be on Time

Abstract: This paper concerns the transfer of files via a lossy communication channel. It formally specifies this file transfer service in a property-oriented way and investigates—using two different techniques—whether a given bounded retransmission protocol conforms to this service. This protocol is based on the well-known alternating bit protocol but allows for a bounded number of retransmissions of a chunk, i.e., part of a file, only. So, eventual delivery is not guaranteed and the protocol may abort the file transfer. We investigate to what extent real-time aspects are important to guarantee the protocol's correctness and use Spin and Uppaal model checking for our purpose. Supported by the NWO/SION project 612-33-006.

Causal Ambiguity and Partial Orders in Event Structures

Abstract: Event structure models often have some constraint which ensures that for each system run it is clear what are the causal predecessors of an event (i.e. there is no causal ambiguity). In this contribution we study what happens if we remove such constraints. We define five different partial order semantics that are intentional in the sense that they refer to syntactic aspects of the model. We also define an observational partial order semantics, that derives a partial order from just the event traces. It appears that this corresponds to the so-called early intentional semantics; the other intentional semantics cannot be observationally characterized. We study the equivalences induced by the different partial order definitions, and their interrelations.

Code Generation based on formal BURS theory and heuristic search

Abstract: BURS theory provides a powerful mechanism to efficiently generate pattern matches in a given expression tree. BURS, which stands for bottom-up rewrite system, is based on term rewrite systems, to which costs are added. We formalise the underlying theory, and derive an algorithm that computes all pattern matches. This algorithm terminates if the term rewrite system is finite. We couple this algorithm with the well-known search algorithm A* that carries out pattern selection. The search algorithm is directed by a cost heuristic that estimates the minimum cost of code that has yet to be generated. The advantage of using a search algorithm is that we need to compute only those costs that may be part of an optimal rewrite sequence (and not the costs of all possible rewrite sequences as in dynamic programming). A system that implements the algorithms presented in this work has been built.