Tessella Support Services - Notation - CAD System for Bank Notes

Counterfeiting has always been a major concern of the Bank of England and traditionally it has used complex patterns to combat the problem. In 1982 The Bank of England commissioned Tessella to aid the writing of a computer design system, called NOTATION. This creates the patterns previously produced using mechanical devices such as the "geometric lathe" and many other effects which could not be generated mechanically. It provides facilities for assembling component pictures into the final designs, including pictures from external sources. Designs are defined using a language which currently consists of 49 drawing instructions each with a subset of 76 possible optional qualifiers. These are supplemented by 50 control commands which also may take qualifiers. Therefore, the NOTATION language is rather complex, especially when using an obscure combination of instructions and qualifiers to produce a novel effect.

The original user interface was a full screen-character cell terminal interface. There were status, instruction list and directive entry areas on the display. When support for graphical user interfaces became readily available it was seen that the use of NOTATION could be greatly simplified by providing dialogs for entry and editing of instructions. All the appropriate qualifiers for an instruction could be presented to the user, avoiding the need to remember which were available. The basic language was to be retained as were the basic features of the interface.

It was clear that more than 100 dialogs would have to be designed and a number of design tools were evaluated to speed up this process. X-Designer was selected for its ability to create the dialogs most quickly and reliably. The widget hierarchy based design method allowed Tessella's experienced programmers to create designs very rapidly. Definitions of sets of widgets were used for areas of dialogs containing common combinations of NOTATION qualifiers. The actual layout was modified using the layout editor after discussions with the customer to determine what they find easiest to work with. Prototyping was easy enough to allow a number of quite different designs to be proposed, often with different distributions of components between main and subsidiary dialogs. This allowed the time needed to write the complex code to translate the content of dialogs into NOTATION language and vice versa.

The majority of the dialog system for the GUI and associated modifications to NOTATION were completed within four months by Tessella and the new interface has been seen as a significant improvement by the users.

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