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Final Report of the COST-247 Action

LotoTis and its Semantics

Ina Schieferdecker

GMD Fokus
Hardenbergplatz 2
D-10623 Berlin
Tel: +30 254 99 241
Fax: +30 254 99 202


LotoTis is a performance-oriented, upward compatible extension of LOTOS. It is a proposal for enhancing LOTOS with

LotoTis can describe Additionally, LotoTis offers a concept of monitoring that allows us to derive any performance measure of interest from a LotoTis specification. Structured actions are the central concept of LotoTis. Such a structured action refines the notion of an action in classical process algebras by a set of parameters which can be used to model real-time and other performance-oriented aspects of system tasks. These parameters are the interaction time, the action priority, the set of requested resources, and the monitoring signal. Structured actions are in general non-instantaneous, may overlap in time, and describe a true concurrent behavior. It is the use of resources that lead us to a new variant of the classical as soon as possible paradigm: an action must occur as soon as it is enabled and (!) the resources have been allocated. Let us notice that the (unspecified) waiting periods for resources may extend to infinity. Thus, minimal delays are specified by the duration of preceding hidden actions, the duration of actions is modelled by non-zero interaction times, and last but not least, maximal delays are described by the use of timeout operators. It will be shown that LotoTis is equally expressive for the description of time-critical behavior like other time proposals for E-LOTOS. However, we argue that the basic LotoTis assumption of waiting as long as necessary for resources and synchronization partners is the only way to describe quantified parallelism by means of resources. LotoTis is an upward compatible extension of LOTOS in two respects. Every LOTOS specification is also a LotoTis specification with equivalent semantics. Every LotoTis specification is a refinement of its underlying LOTOS specification. Hence LotoTis supports for the development of performance-oriented specification from existing LOTOS specifications using a number of refinement rules. After an introduction into LotoTis we will present its semantics. We use the intermediate specification language GENIUS. GENIUS is an upward compatible extension of LOTOS in the sense that it extends LOTOS with additional features while preserving the original LOTOS semantics. GENIUS has an operational semantics. LotoTis is transformed to GENIUS in order to define the LotoTis semantics. These two steps of semantics definition (from LotoTis to GENIUS, then from GENIUS to SLTS) will be discussed. Afterwards, properties of LotoTis are given.

This presentation has been given during the COST-247 4th Management Committee Meeting (Berlin, Germany, February 9--10, 1995).

COST-247 Working Group(s): 1-4

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