Necessity of a Graphical Language

Displays in control process applications are considered to have 2 major uses:

- To create and show pictures - To operate with them.

These uses imply the display working as an input-output equipment for the digital computer. In both cases the opera­

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-tor of the display console constitutes an essential part of the complete system, for he follows according to his ob­

jectivée the procedure established in creating pictures and when operating with the particular picture shown by the dis­

play unit, he analyzes it to take, when required, the most convenient decisions.

Creation of pictures must be a task carried out off-line in order to avoid the obstruction of the normal operation of the computer. On the other hand, operation with them must be

carried out on-line, so that the process and the computer can be influenced in real time by the decisions taken each time by the operator from the display console.

In creating the pictures, the following alternatives can be used by the operator, namely:

1. Using some means which permit him to select directly the symbols of components /i.e. valves, pumps, and so on/ to be included in the picture.

In this case there must directly be available to the op­

erator all the symbols corresponding to all possible different graphical elements to be used in creating the particular picture. This can be accomplished either by using a special keyboard with the symbols labeled over each key, or by creating on the screen a bulky "menu"

with all available symbols arranged conveniently for se­

lecting each time that required to create the picture, or creating manually their particular codes by means of some keys, each one corresponding to each bit position of the

code, etc. On the one hand, due to the relatively high number of different symbols required for each picture, to the limited size of the useful surface of the display’s screen, to the additional capacity required to store the

’'menu” into the display’s refresh memory and others, the

"menu" solution is here neglected.

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-On the other hand, by using one key for each bit position of the code /considering equal-length codes as the solu­

tion used/ and to create manually each time the code of the symbols required for the picture implies a quite time- consuming task for the operator and easily committed

errors; to "prepare" the picture cell by cell giving also each time the corresponding color to the symbols; to have to know previously how those complex symbols which occupy more than one cell on the screen can be constructed with the Symbol-set available for the equipment, and so on. All these inconveniences, among others, lead us to neglect this solution also.

Therefore, from these three possibilities the use of the special keyboard with all the available symbols labelled in different keys as input means seems more commendable.

The use of this solution to create pictures would present the following advantages:

- The task can be carried out in a similar form as when an alphanumerical display is used for editing, having thus all its advantages.

- It requires a simple coloured sketch drawn on paper of the picture to be created, it being necessary only to reproduce it directly.

- It permits us to create directly any type of mentally conceivable picture without taking into account special geometric rules, rigid formats, particular instructions, etc.

- It does not require the contribution neither of the computer nor of the Controller in "editing" the pic­

tures, since they can be prepared off-line in a stand­

alone display.

- It permits the operator to perform continuously and directly the visual correction of the picture being

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-created as in the case of alphanumerioal displays.

- After code conversion to the graphical code designed for the display itself, the transmission of the information to the computer memory can be performed in a straight­

forward form, but in a cell-by-cell and orderly fashion.

- It does not require highly trained operators.

Disadvantages of this solution are:

- It requires an additional labelling for the keyboard’s keys commonly used for editing, or otherwise, a

specially designed independent one to be used only to create the pictures.

- The operator needs to know previously how complex symbols occupying several adjacent cells can be con­

structed with the Symbol-set available for the equip­

ment.

- It makes it difficult to do reverse code conversion in order to permit the use by the system of those graphical subroutines created to represent graphically the

complex symbols requiring several adjacent cells, or any other type of compressed instruction.

- It does not permit the creation of new graphical sub­

routines such as those which can be created and used when particular parts of given pictures are repeated several times, or a new complex symbol is included in the picture, etc.

- It would require a constant memory capacity per picture to be programmed, independently of the characteristics of the picture /complexity, proportion of straight lines respect to alphanumeric characters or single symbols, etc./, that is, it does not permit us to save computer memory locations by means of a given data-compression solution.

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-- It requires some artistic aptitude and aesthetic

appreciation from the operator /or from the programmer/

mainly when a complex symbol composed of many single symbols must be included in the picture /i.e. a pump symbol/, or when a complex drawing must be realized#

- It would require a considerable time from the operator.

We will now analyze a second alternative.

2. By using a specially created graphical language having all