STATE-CHARTS

State-Charts



State-Charts

Introduction

A report highlighting the deficiencies inherent in conventional state machine modelling, and the features of Statechart modelling that facilitate the design of a solution by overcoming these deficiencies. The report also compares Statechart modelling with CSP and draws attention to their differences and similarities. The modelling facilities provided by the conventional state machine modelling technique are used frequently to model real time systems. Real time systems are based upon events happening to which the system responds, and then transitions to another state. This directly maps onto the state machine model for simpler systems.

This report examines the paucity of support for concurrent systems, which have an increasing role in real time systems, and how these deficiencies are recognised and overcome in the Statechart modelling paradigm. The report will then compare and contrast the roles Statecharts modelling and CSP have when developing more complex systems.

Statement of the problem

There have been a few papers published related to this problem. The task is to

Implement one of the simple well-described methods for construction of a state-machine from a number of interaction diagrams. An illustration is shown below.

Identify approaches for building hierarchical state-transition diagrams from scenarion and/or machines produced from scenarios above.

Background

In many cases, the intended behaviour of software is described through UML interaction diagrams (also known as MessageSequence charts), which can be viewed as a refinement of UML use cases. There does not appear to be many automated approaches to build hierarchical and concurrent diagrams for a system to satisfy the constructed interaction diagrams.

Literature review

Conventional State Machine Modelling

Explanation

State Machine Modelling is concerned with modelling the system which it describes as a collection of discrete sates. State machines model these states in a language independent manner. The state model of a system is always in one of its set of possible states, the model transitions from one state to another system state when stimuli are received.

Limitations

There are limitations to the use of conventional state machine modelling.

One of the limitations inherent in conventional state machine modelling techniques is the complexity of the state diagram increases dramatically as the number of possible states increases. The state machine model then becomes unwieldy to use, this detracts from the intended purposes of state machine models, to allow the system to be modelled in a more comprehensible manner.

Another of the limitations of modelling a computer system as a conventional state machine is the lack of support for concurrent constructs. Traditional state machine modelling is based on sequential transitions from one state to the next. Concurrent systems cannot be modelled in this manner as various aspects of the system may be in different states.

It is seen that the limitations inherent in state machine models include the inherent complexity which occurs as the number of states increases, and also the modelling of concurrent systems.

Statechart Modelling

Explanation

State machine modelling is the basis for various real-time methods such as that proposed by Ward and Mellor (1985) and Harel (1987). This section details how Harel's method, Statechart modelling, overcomes the limitations of conventional ...