Programming compensations for system-monitor synchronisation

In security-critical systems such as online establishments, runtime analysis is crucial to detect and handle any unexpected behaviour. Due to resource-intensive operations carried out by such systems, particularly during peak times, synchronous monitoring is not always an option. Asynchronous monitoring, on the other hand, would not compete for system resources but might detect anomalies when the system has progressed further, and it is already too late to apply a remedy. A conciliatory approach is to apply asynchronous monitoring but synchronising when there is a high risk of a problem arising. Although this does not solve the issue of problems arising when in asynchronous mode, compensations have been shown to be useful to restore the system to a sane state when this occurs. In this paper we propose a novel notation, compensating automata, which enables the user to program the compensation logic within the monitor, extending our earlier results by allowing for richer compensation structures. This approach moves the compensation closer to the violation information while simultaneously relieving the system of the additional burden.peer-reviewe

Recovery within long running transactions

As computer systems continue to grow in complexity, the possibilities of failure increase. At the same time, the increase in computer system pervasiveness in day-to-day activities brought along increased expectations on their reliability. This has led to the need for effective and automatic error recovery techniques to resolve failures. Transactions enable the handling of failure propagation over concurrent systems due to dependencies, restoring the system to the point before the failure occurred. However, in various settings, especially when interacting with the real world, reversal is not possible. The notion of compensations has been long advocated as a way of addressing this issue, through the specification of activities which can be executed to undo partial transactions. Still, there is no accepted standard theory; the literature offers a plethora of distinct formalisms and approaches. In this survey, we review the compensations from a theoretical point of view by: (i) giving a historic account of the evolution of compensating transactions; (ii) delineating and describing a number of design options involved; (iii) presenting a number of formalisms found in the literature, exposing similarities and differences; (iv) comparing formal notions of compensation correctness; (v) giving insights regarding the application of compensations in practice; and (vi) discussing current and future research trends in the area.peer-reviewe

A compensating transaction example in twelve notations

The scenario of business computer systems changed with the advent of cross-entity computer interactions: computer systems no longer had the limited role of storing and processing data, but became themselves the players which actuated real-life actions. These advancements rendered the traditional transaction mechanism insufficient to deal with these new complexities of longer multi-party transactions. The concept of compensations has long been suggested as a solution, providing the possibility of executing “counter”-actions which semantically undo previously completed actions in case a transaction fails. There are numerous design options related to compensations particularly when deciding the strategy of ordering compensating actions. Along the years, various models which include compensations have emerged, each tackling in its own way these options. In this work, we review a number of notations which handle compensations by going through their syntax and semantics — highlighting the distinguishing features — and encoding a typical compensating transaction example in terms of each of these notations.peer-reviewe