Performance-Oriented Formal Specifications -- the LoToTIs Approach Ina Schieferdecker GMD FOKUS, Hardenbergplatz 2, D-10623 Berlin tel: § 30 254 99 170~ e-mail: ina@fokus.gmd.de, http://www.fokus.gmd.de/htbin/info/minos/ina Abstract. The paper presents the performance-oriented, LOTOS exten- sion LoToTIs. LoToTIs allows us to specify performance-oriented be- havior via quantified time~ quantified nondeterminism~ quantified par- allelism, and action monitoring. It offers a set of refinement rules from LOTOS to LoToTIs. Therefore~ LoToTIs supports the standard conform development of performance-oriented specifications from existing LOTOS specifications. 1 Performance Evaluation based on Formal Specifications In the mid eighties [10] there was already recognized that specifying perfor- mance requirements can be as important as specifying functional requirements of distributed systems. However, formal specification techniques covered so far primarily functional aspects for the investigation of the functional correctness of distributed systems. Hence, it was (and is still) not unusual that a system is fully implemented or at least implemented as a prototype before any attempt is made to investigate its performance. However, costly re-prototyping or re- implementation can be avoided, if performance could be predicted from the specification of a distributed system. A framework, which supports functional and performance-oriented behavior specification, and which allows us to evalu- ate performance from that specification would offer major advantages. For this purpose, new concepts have to be incorporated into formal specification tech- niques. Only recently, there had been published some proposals that close the gap between formal specification and performance evaluation [1]. This paper presents the LoToTIs approach that is a newly-designed perfor- mance-oriented formal description technique (FDT). Its main advantage is the upward compatibility with LOTOS that is one of the internationally standard- ized FDTs [5]. After introducing the main concepts of LoToTIs, we present the language and give an insight into its semantics. The most important properties of LoToTIs are given. The paper finishes with a methodology based on the Lo- Tos/LoToTIS framework that supports the development of standard conform prototypes and the prediction of their performance.