Stochastically timed predicate-based communication primitives for autonomic computing

Abstract

Predicate-based communication allows components of a system to send messages and requests to ensembles of components that are determined at execution time through the evaluation of a predicate, in a multicast fashion. Predicate-based communication can greatly simplify the programming of autonomous and adaptive systems. We present a stochastically timed extension of the Software Component Ensemble Language (SCEL) that was introduced in previous work. Such an extension raises a number of non-trivial design and formal semantics issues with different options as possible solutions at different levels of abstraction. We discuss four of these options, of which two in more detail. We provide a formal semantics and an illustration of the use of the language modeling a variant of a bike sharing system, together with some preliminary analysis of the system performance.

Investigating Fluid-Flow Semantics of Asynchronous Tuple-Based Process Languages for Collective Adaptive Systems

“…One possibility is to take StoKLAIM [11] as a starting point, thus using a simple, locality based approach. Another, perhaps more interesting possibility, instead, is to use a richer, predicate based, addressing mechanism, like (a possibly restricted version of) the addressing mechanism of StocS [20], where the location is just one of the agents' attributes and its values are instances of an appropriate data type, namely space. This can take different forms, from topological spaces-including bi-or tri-dimensional continuous space-to more general closure spaces-including generic graphs-as in [6].…”

“…Examples include KLAIM [10], which extends LINDA with, among others, a notion of space, the TOTA framework [21], which, additionally, provides for explicit adaptive tuple propagation mechanisms and a sort of force field view of tuples, and SCEL [8], where the basic interaction paradigm is enriched with a flexible, predicate-based addressing mechanism, with a framework for defining policies, and with a notion of tuple-space which is extended to a more general knowledge-space. Additionally, quantitative extensions of both KLAIM and SCEL have been developed, namely StoKLAIM [11] and StocS [20], where the quantity of interest is the duration of (the execution of) process actions. Such durations are assumed to be continuous random variables with negative exponential distributions, commonly used in stochastic process algebra [17].…”

The SCEL Language: Design, Implementation, Verification

“…However, the main challenge in developing a stochastic semantics for SCEL is in making appropriate modeling choices, both taking into account the specific application needs and allowing to manage model complexity and size. Our contribution in this work is the proposal of four variants of StocS, a Markovian extension of a significant fragment of SCEL, that can be used to support quantitative analysis of adaptive systems composed of ensembles of cooperating components [32]. In this chapter, we focus on only one of the four variants, the so called Network oriented one (net-or, for short).…”

“…In this chapter, we focus on only one of the four variants, the so called Network oriented one (net-or, for short). The reader interested in the full spectrum of StocS semantics and their complete formal definition is referred to [32] and to the technical report [33]. In summary, StocS is essentially a modeling language which inherits the purpose and focus of SCEL.…”

Specification and Analysis of Open-Ended Systems with CARMA

“…Attributes from the knowledge base are used by components to dynamically form ensembles and to select partners for interaction. The stochastic variant of SCEL, called StocS [15], has been used to investigate a number of different stochastic and probabilistic semantics. Moreover, SCEL has inspired the development of the core calculus AbC [16] that focuses on a minimal set of primitives that defines attribute-based communication without the rich underlying knowledge base, and investigates their impact.…”