We present a broad extension of the conventional formalism of state machines and state diagrams, that is relevant to the specification and design of complex discrete-event systems, such as multi-computer real-time systems, communication protocols and digital control units. Our diagrams, which we call statecharts, extend conventional state-transition diagrams with essentially three olements, dealing, respectively, with the notions of hierarchy, concurrency and communication. These transform the language of state diagrams into a highly structured' and economical description language. Statecharts are thus compact and expressive--small diagrams can express complex behavior--as well as compositional and modular. When coupled with the capabilities of computerized graphics, statecharts enable viewing the description at different levels of detail, and make even very large specifications manageable and comprehensible. In fact, we intend to demonstrate here that statecharts counter many of the objections raised against conventional state diagrams, and thus appear to render specification by diagrams an attractive and plausible approach. Statecharts can be used either as a stand-alone behavioral description or as part of a more general design methodology that deals also with the system's other aspects, such as functional decomposition and data-flow specification. We also discuss some practical experience that was gained over the last three years in applying the statechart formalism to the specification of a particularly complex system.

Formal and semiformal specification techniques have been applied to many aspects of software development. Their value is that they permit a designer to describe precisely the external

. Modern window-based user interfaces are actually a special kind of reactive system, and Petri nets may be fruitfully used to design such user - computer dialogues. This paper describes a software engineering tool aimed at supporting the use of high-level Petri nets for the specification, design and implementation of user interfaces in an event-driven interface system. We assess the rationale for the use of Petri nets in such a perspective. We then detail the object-oriented software architecture of the environment, and present an original algorithm for interpreting high-level Petri nets in an event-driven environment. Key-words : User Interface, Design, Computer tools for nets, High-level Petri nets. Contents 1. Introduction __________________________________________________________ 1 2. Event-driven programming ______________________________________________ 2 3. Architecture of interactive systems ________________________________________ 5 4. Designing event-driven interfaces wit...

Over the last few years, Model-Based User Interface Design has become an important tool for creating multi-device User Interfaces. By providing

Statecharts is a behavioural specification language for the specification of real-time event driven reactive systems. Recently, statecharts was related to a logical specification language, using which safety and liveness properties could be expressed# this language provides a compositional proof system for statecharts. However, the logical specification language is flat, with no facilities to account for the structure of statecharts; further, the primitives of this language are dependent on statecharts syntax, and cannot be related directly to the problem domain. This paper discusses a temporal logic-based specification language called FNLOG which addresses these problems.

It is usually very hard, both for designers and users, to reason reliably about user interfaces. This article shows that ‘push button ’ and ‘point and click ’ user interfaces are algebraic structures. Users effectively do algebra when they interact, and therefore we can be precise about some important design issues and issues of usability. Matrix algebra, in particular, is useful for explicit calculation and for proof of various user interface properties. With matrix algebra, we are able to undertake with ease unusally thorough reviews of real user interfaces: this article examines a mobile phone, a handheld calculator and a digital multimeter as case studies, and draws general conclusions about the approach and its relevance to design.

Manuals and interactive help are tedious to provide, difficult to maintain, and difficult to ensure correct, even for simple systems. The result is a loss in product quality, felt particularly by users and designers committed to long-term product development. This paper

This report gives a survey of user interface languages and formal representations of user interfaces. The following aspects of User Interface Languages are considered: ffl expressiveness ffl readability ffl evaluation (is it possible to evaluate the ergonomic and functional quality of the user interface from the representation) ffl manipulation ffl compilation/interpretation ffl possibility to include knowledge representation.

In this paper we investigate a component-based approach to combining formal techniques and prototyping for user interface construction in which a single specification is used for constructing both implementations (prototypes) for experimentation and models for formal reasoning. Using a component-based approach not only allows us to construct realistic prototypes, but also allows us to generate a variety of formal models. Rapid prototyping allows the designs to be tested with end users and modified based on their comments and performance, while formal modeling permits the designer to verify mechanically specific requirements imposed on the user interface such as those found in safety- or security-critical applications. 1 Introduction User interfaces can be difficult and costly to construct; one recent survey estimates that half the development effort for an interactive application is spent on constructing the user interface [MR92]. It is natural to attempt to apply software engineering...

It is useful to be able to specify a proposed human-computer interface formally before building it, particularly if a mockup suitable for testing can be obtained directly from the specification. A specification technique for user interfaces, based on state transition diagrams, is introduced and then demonstrated for a secure message sys-tem application. An interpreter that executes the resulting specification ~s then described. Some problems that arise in specifying a user interface are addressed by particular features of the technique: To reduce the complexity of the developer's task, a user interface is divided into the semantic, syntactic, and lexical levels, and a separate executable specification is provided for each. A process of stepwise refinement of the syntactic specification, leading from an informal specification to an executable one is also presented. Since the state diagram notation is based on a non-deterministic model, constraints necessary to realize the system with a deterministic interpreter are given. Writing a formal specification of the user interface of a computer system before building it permits the interface designer to consider a variety of possible user interfaces and describe them precisely and compactly without actually having to code them. It also permits the appli-cation of human performance models to the specifications to obtain information about the user interfaces they describe before building them [1, 15]. The specifications can be checked for certain undesirable properties of the user interface, such as almost-alike states [14], interactive deadlock [4], and character-level ambiguity [18]. Further benefits accrue if a pro-totype or mockup of the user interface of the proposed system can be constructed directly from the specification. Problems with the pro-posed user interface can then be identified early in the design process, when they are easier to fix. While many prcspective users will f_nd a for-mal specification of a proposed system difficult to understand, they will have much less trouble evaluating a mockup system and identifying deficiencies in its user interface, both through informal demonstrations and formal experi-