. In this paper we apply a new real-time modeling to the wellknown Steam Boiler case study. The novelty of our approach is in explicitly representing the various system components, i. e. hardware sensors, software controllers and so on, with separate local clocks. The aim of our approach is to be able to statically analyze the global system specification taking into account the relative speed of each system components. For example, we can statically verify if, and how changing the local speed of a component can affect the global performance of the system. Component behaviors are specified by means of a simple process algebra. Local clocks are modeled as higher order terms in a given signature, and unification is used to define the common clock. Then an operational semantics defines which transitions a process can perform and which transitions let time to elapse. 1 Introduction In this paper we apply a new real-time modeling to the well-known "The Steam Boiler" case study ...

. Nowadays, more and more often, complex systems are built by assembling together different system components. This technology also affects the construction of heterogeneous and/or hybrid systems where components can represent hardware sensors, software controllers, etc. Moreover the resulting system is normally distributed. These systems have often real-time constraints/requirements and each component is characterized by its own speed determined by its local clock. Configuring a system out of such components means to be able to determine a given global clock of the system defined in terms of the various local clocks. In this paper we present a framework in which it is possible to specify and statically analyze the architecture of a system as a network of (parallel) components, each one with its own local clock. Then configuring the system means to formally define how to get the global clock out of the local clocks. This clock configuration step is "optimal" that is, it i...

A real-time computer system is a system that must perform its functions within specified time bounds. These systems are generally characterized by complex interactions with the environment in which they operate and strict time constraints whose violation may have catastrophic consequences. The need for these software systems to be highly reliable is evident. One way to achieve this reliability is through formal development. Although research in the area of real-time systems has been quite active and a number of experimental environments supporting formal specifications have been developed, the search for adequate notations and tools is still ongoing. In order to get designers to use formal methods to develop real-time systems it is necessary to provide them with an integrated set of tools for writing and analyzing their specifications. The ASTRAL Software Development Environment (SDE), which is an integrated set of tools based on the ASTRAL formal framework, is intended to meet this need. The tools that make up the support environment are a syntax-directed editor, a specification processor, a verification condition generator, a mechanical theorem prover, and a browser kit. This paper discusses the goals for ASTRAL, why they were important, and how they were met. It will also give an overview of the ASTRAL Software Development Environment.

ASTRAL is a high-level formal specification language for real-time systems. It includes structuring mechanisms that allow one to build modularized specifications of complex real-time systems with layering. Based upon the ASTRAL symbolic model checker reported in [DK99b], an approximation technique to speed-up the ASTRAL symbolic model checker for debugging a specification is presented. The technique, called dynamic environment generation, randomly generates a sequence of concrete environments for an ASTRAL process instance along each execution path in the execution tree of the ASTRAL process. Doing this greatly reduces the time for finding an error in a specification, as demonstrated by a number of mutation tests, while still ensuring reasonable coverage of the search procedure. The results of the tests show that the techniques presented in the paper are effective.

Literature on Unified Modeling Language (UML) and aspect-orientation often focus on improving the software development process [2]. This paper presents a systems engineering perspective that motivates an aspect-oriented software architectural analysis approach using representations of UML models. This approach is important in contributing to the direction of applying aspectorientation with UML because it attempts to bridge the gap between software development projects that initiate or follow the recommended research directions in the literature with those that unfortunately, and too frequently, do not.

information flow in identity management systems

Refinement is a fundamental design technique that has often challenged the "formal methods" community. In most cases, mathematical elegance and proof manageability have been chosen over flexibility and freedom, which are often needed in practice to deal with unexpected or critical situations. The issue of refinement becomes even more critical when dealing with real-time systems where time analysis is a crucial factor. In this case, the literature exhibits only a few, fairly limited proposals. In this paper, we propose general refinement mechanisms for real-time systems that allow several types of implementation strategies to be specified in a fairly natural way. Not surprisingly, generality has a price in terms of complexity. In our approach, however, this price is paid only when necessary. Furthermore, the proof system is amenable both for traditional hand-proofs, based on human ingenuity and only partially formalized, and for fully formalized, tool-supported proofs. The following is...

Region reachability is useful, but obviously not enough. For instance, we may wantto know whether clock values satisfying a non-region property

The paper [CH85] presents a mathematical model of real time systems behavior, suitable for requirements specification, analysis and proof of properties. Content. Time is considered, almost always, a discrete set, but it may be uncountable (a the set R). Events (as sequence of occurrences of a certain event) are modeled by a function time from N to Time. This function binds the i-th occurrence of an event to its time of occurrence, and it has some restrictions (increasing ...). More than one occurrence at the same time of an event are allowed. Moreover the non Zeno requirement is modeled by a simple requirement of this function ( lim n!1 time(e)(n) = +1). This requirement prevents an event from occurring in nitely often during a finite delay. Variables are introduced. They are piecewise constant, because their assignment to a value is an event. Periodic events (with fixed and variable period) are defined as well. They define counters of events too. There are counters of two types: lcoun...

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