An Introduction to Lotos through a Worked Example

The practical application of formal description techniques (FDT's) is becoming increasingly important in computing. However, there remains a gulf in the literature between the language of application developers and the more theoretical language often used to describe formal methods. The aim of this paper is to try to bridge this gap by introducing the formal description technique, LOTOS, in a non-theoretical manner. The main features of LOTOS are introduced through a worked example, a speciica-tion of a multi-way phone system. This example was chosen because the speciication is compact and yet is suuciently complex to introduce most LOTOS features. Furthermore , the protocols involved in a multi-way phone are intuitive. The paper also stresses the importance of supporting tools in the development of formal speciications and presents two tools, namely SEDOS and CCSAR/ALD EBARAN, and explains why they are important in the speciication process.