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SELECT Yourdon

Select Yourdon in use screen shot

Real Time CASE Tool

Running on a PC under Microsoft Windows, SELECT allows those with a small budget to enjoy the benefits of using a CASE tool to design and document their products.

Context diagramSELECT allows standard symbols to be used to draw relationships between data, processes and events. Each entry has a database record associated with it that holds all relevant data about the entry along with comments. At the lowest level structured English statements may be used in mini-specs (sometimes known as PSPECs) to specify modules.

With its ability to model the three major aspects of a software system (functionality, data and timing), the Yourdon method has found favour with many of the world's software developers especially those involved with real-time applications. It is also considered to be a good starting point for beginners, since the notation is relatively easy to understand and there are many excellent books and courses available.

Data flow diagramData and Control Flow diagrams - are the basis of the Ward-Mellor and Hartley methods both notations are supported.

The design can be browsed interactively and when creating lower level designs the system will prompt with details of the links into the new level. The software can check designs for consistency, completeness and level to level balancing (are all the inputs at a higher level shown at the next level?). This includes checks between state diagrams and their control flow diagrams as well as checking that PSPECs operate on their input and output data flows.

One of the attractions of the SELECT package is that different aspects of the problem may be designed and documented using whichever tool is the most appropriate.State machine diagram

State Transition diagrams - are important for modelling the systems reactions to events.

Chen Entity relationship diagrams - are used where complex data structures are to be represented.

Both Jackson and Constantine structure charts - are provided for representing the programs execution.

A comprehensive data dictionary - is created as the design is produced and this may be browsed, cross-checked and reported upon.

Title: Fire Alarm System
Date: 2-Mar-93 Time: 17:58

Report: Data Dictionary

NAME = Alarm Event
TYPE = Control flow
@COMMENT The fact that a sensor or pseudo sensor has changed status.

NAME = Alarm Queue
TYPE = Store
@COMMENT This is a time ordered circular list of sensors "in alarm" but not yet accepted by the operator.

Select Yourdon Pro £1200

C++ Real Time Design

Things are moving fast in the production of CASE tools for C++. The latest news is that they locked the gurus up in a very expensive hotel up in the mountains and told them not to come out until they had agreed upon a design methodology and a  diagramming scheme. And low they came down from the mountains with Unified Modelling Language (which is so much easier to remember than Yourdon, Hatley, Parnas, Gomaa, Booch, Jacobson, Rumbaugh).

Among other useful representations UML includes the Sequence Diagram which seems to me to provide a powerful design tool as opposed to simply a documentation aid. If we look at a design consisting of a number of objects then the Sequence Diagram (SD) shows how these objects interact (pass messages). This message passing may then change the state of the object (use a State diagram to show this). The SD has links upwards to the Specification (so called ‘Use Cases') and downwards to the objects and their implementation in the class diagram. The pseudo code of the Use Case included in the SD should in the future provide a code skeleton for the application. If implemented using a multi task operating system (CMX or chipFORTH) the SD also maps well to a task interaction diagram.

For those designing large object oriented programs in C++ or Visual Basic (particularly if they include complex data-bases) Select Enterprise follows the UML standard and gives both code generation and model generation from code.

But UML on it's own does not provide all the tools required by designers of Real Time Embedded applications. Artisan Software is a spin off from Select who have defined a set of real-time extensions to UML that additionally cover: The system's reaction to events, time constraints, concurrent tasks and partitioning applications across multiple processors. Documenting all of these is integrated into a single design tool.

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