Specifying and executing behavioral requirements: the play-in/play-out approach

Abstract

Abstract. A powerful methodology for scenario-based specification of reactive systems is described, in which the behavior is "played in" directly from the system's GUI or some abstract version thereof, and can then be "played out". The approach is supported and illustrated by a tool, which we call the play-engine. As the behavior is played in, the play-engine automatically generates a formal version in an extended version of the language of live sequence charts (LSCs). As they are played out, it causes the application to react according to the universal ("must") parts of the specification; the existential ("may") parts can be monitored to check their successful completion. Play-in is a user-friendly high-level way of specifying behavior and play-out is a rather surprising way of working with a fully operational system directly from its inter-object requirements. The ideas appear to be relevant to many stages of system development, including requirements engineering, specification, testing, analysis and implementation.

Practically Applicable Formal Methods

“…A formal method designed for the real market cannot increase development costs too much. The "80/20" rule applies to the development process: 20% of work produces 80% of a project -big parts of systems can even be generated automatically from requirements or specifications [16], so business managers may expect the same from formal methods. Thus we should provide them solutions that cover automatically at least 80% of the code and leave the remaining 20% (often unclear, messy and unnecessarily complicated) to be reviewed by the programmers.…”

On the Power of Play-Out for Scenario-Based Programs

“…Play-out, defined in [12,11], is a recent example of a different approach. Instead of synthesizing intra-object state-based specifications for each of the components, the play-out algorithm executes the scenarios directly, keeping track of all user (or environment) events, as well as system events, for all objects or components simultaneously, and causing other events and actions to occur as dictated by the specified scenarios.…”

Why Timed Sequence Diagrams Require Three-Event Semantics

“…Harel has also been involved in the development of a tool-supported methodology that uses LSC as a way to prescribe systems as well as verifying the correspondence between manually described LSCs and State Machines [HM03].…”