The Arabic script is written from right to left and is essentially and obligatorily cursive: letters are horizontally linked to one another without the intervening blank spaces customary in the printing of European languages. The writing of Arabic in a simplified form involving the intrusion of such spaces has been implemented in order to facilitate the use of equipment and procedures originally designed for Western languages, but the results are invariably unacceptable from an esthetic point of view. To achieve a tolerable compliance with the ordinary calligraphic style, a variety of shapes must be provided for most letters of the alphabet. This is done, for instance, on the usual Arabic typewriter keyboard. Of course the selection of the appropriate form of each letter devolves upon the typist, even though this choice is completely determined by the orthographic context, specifically, by the immediately preceding and the immediately following character. This implementation necessitates a multiplication of the number of keys and so results in a reduction of typing speed, especially since many of the variant shapes are on shifted keys. (The Arabic script does not have the upper-case vs. lower-case distinction of Western typography). In any case, Arabic typewriters must reduce the inventory of variant forms to limit the size of the keyboard, and this results in a definite degradation of the quality of the Arabic script produced, as judged by the standards of either traditional manual calligraphy or full-scale typographic composition.
A further problem is that the shape assumed by most letters depends on the following character, which cannot be known in advance. Usually one must know what character follows the present one before one can draw it correctly. Hence a lag in response to the user is introduced in those few proposed systems where an effort is made to relieve the typist of the task of selecting the particular form of each letter as well as the letter itself.
In summary, existing devices suffer from one or more of the following drawbacks:
(1) calligraphically poor output due to over-simplification of the cursive script;
(2) imposition on the user of the (unnecessary) task of selecting the particular context-determined form of each letter;
(3) delay in response to user input when subsequent context is unknown.