الأبجدية العربية

The Arabic alphabet

28 letters make up the Arabic alphabet and quite a few extra symbols are required for proper text input, like the hamza in its different shapes أ إ آ ء ئ ؤ, ta marbutah ة, alif maqsurah ى and various diacritics for vowelized texts. Since the performance of a keyboard layout depends on the text entered it is necessary to study its mono-, di- and trigraph frequencies first. The novel corpus built for the following analysis consists of

{% for c in corpus|sort(attribute='source.name') %} {% set count = c.get ('count') %} {% if count %} {# use new style formatting, for some reason %7,d does not work #} {% else %} {% endif %} {% set stats = c.get ('stats') %} {% for k in ('words', 'characters') %} {% set i = stats[k]|approx %} {% endfor %} {% endfor %} {% for k in ('words', 'characters') %} {% set i = corpustotal[k]|approx %} {% endfor %}

Source		Words	Characters
{{ c.source.name }}	{{ '{:7,d}'.format(count[0])|numspace }} {{ count[1] }}		{{ '%5.1f'|format(i[0])|numspace }} {{ i[1] }}
Total		{{ '%5.1f'|format(i[0])|numspace }} {{ i[1] }}

The plot below shows ا ل ي م و ن can be considered the most frequently used letters in the Arabic language. Together they account for more than 55% of all letters in the corpus.

Layout properties

Throughout this evaluation color coding is used to identify fingers:

red

little finger

blue

ring finger

magenta

middle finger

violet

index finger

cyan

thumb

Asymmetry is defined as the difference between left and right hand usage.

The layout proposed uses four layers and assumes a 102/105 key ISO keyboard common in Europe to accomodate the shift keys necessary. These are in order: Shift on the left and right, caps lock on the left and the rightmost key in the middle row, the key right of the left shift key and the key labeled Alt Gr to the right of the spacebar. Symbols are assigned to the four layers by their function: characters, punctuation, diacritics, other.

The first layer was optimized using an extended reimplementation of carpalx. From several runs with 100.000 iterations each the layout which had good scores and looked reasonable to the human eye was picked. Optimal arrengement of layers two and up are still under investigation.

The most frequent letters have all been assigned to the home row, which makes them easily accessible. ا and ل are typed with different hands, balancing the load on hands almost evenly. The index and middle finger of both hands share the majority of the typing load, but naturally the left middle finger is used more frequently due to its assignment to the letter alif.

Related work

This section explores existing keyboard layouts made for the Arabic language and analyzes their usability.

ASMO 663

Trying to unify existing layouts, the Arab Standardization and Meterology Organization (ASMO), now part of AIDMO, published an Arabic keyboard layout in 1987 as standard 663 titled Arabic terminal keyboard layout. The layout has several shortcomings: Most notably it clusters letters by their visual similarity (ض ص، س ش، ح ج خ) and not frequency. Also it overuses the right index finger by assigning the four high-frequency letters ا ت و ة to it.

Mac OS X

Mac OS X’s Arabic keyboard layout makes a few small changes to ASMO 663 by moving the ة to a hard to reach spot on the right of the top row. It also moves the short vowels from the first to the top row of the second layer and replaces them with symbols. The bottom row keys are aditionally shifted to the right, beginning with ر.

In contrast to the layouts presented so far the following layouts claim to be optimized for the Arabic language and were, at least partially, created algorithmically.

Al-Ramly et al

One of the eariest accounts can be found in the article Statistical Distribution of Arabic Letters Aids to the Design of a New Keyboard by Al-Ramly et al published in 1980. The Arabic half of the proposed bi-lingual layout seems to be hand-optimized based on several metrics including character frequencies – without mentioning a source for them though – visual similarity (“letter groups”) and their position on previous layouts. It tries to balance load between hands, assign more work to index and middle fingers and place common letters in the home row. However the asymmetry given in the article, 0.032, cannot be reproduced here. For the most part the layout lacks combining and pre-combined characters, a task that is left to “machine intelligence” making it hard to use nowadays.

While the layout distributes load between fingers quite well it favors the left hand by assigning ا and ل to it. The decision to place ث in a very prominent spot seems weird, given it only accounts for 0.5% of all symbols, even in their own analysis.

Idlebi et al

Another article from the early days of computers published in 1990 is Design of Arabic Keyboard Layout Based on Statistical Properties of Arabic Characters by Idlebi et al. They present two examples of programmatically optimized layouts and account for character and bigram frequencies based on a corpus of 100.000 characters, finger movement time of unknown origin and finger load.

Unfortunately the results use 12 keys per row and are not suitable for use with current European keyboards, which usually feature only 11 keys in the bottom row. Thus the layout displayed below lacks the Arabic question mark and comma in the bottom right. Probably due to their unusual assumption that middle- and ring-finger rest in the top row their results are suboptimal, placing both ا and ي in the top row. Their analysis notices this and suggests improved positions for both characters, but these are not actually implemented. The big asymmetry is caused by placing ا ل ي and و, four of the five most frequent letters, on the right hand side.

Malas et al

About 20 years later (2008) Malas et al. presented an alternative layout generated by a genetic algorithm in their article Toward Optimal Arabic Keyboard Layout Using Genetic Algorithm. They used a snapshot of the Arabic Wikipedia probably from around 2008 and optimized for typing speed only, claiming 35% faster typing compared to the currently used layouts. However the decision to put ي in the top row seems odd. Assigning the same left index finger to ا ي و, which are three of the most frequent letters, heavily strains this particular finger.

Khorshid et al

In figure 8 of the paper A new optimal Arabic keyboard layout using genetic algorithm published in 2010 Khorshid et al. present yet another layout. They reject the idea of using contemporary text sources like newspapers or books and consequently their only input text is a copy of the Quran, whose distribution of mono- and digraphs is quite different from modern, non-religious texts. A 36% improvement over the standard keyboard based on their criteria for ergonomic layouts is claimed in their conclusion as well. However their algorithm seems to favor the bottom row instead of the easier to use top row since it places the letters ب ت ر there.

Osman et al

In 2015 patent 9,041,657 B2 was filed in the US, presenting yet another computer-generated layout. Its genetic algorithm was seeded with just 54 Arabic e-books consisting of 7 million characters in total. Overall it claims to be 9% faster than default layouts. This layout rips off most of the standard layout’s second layer, but amusingly fails to include a question mark, while it does provide three single-quote marks ’ and two Arabic semicolon ؛. Additionally it places ي in an even worse position than Malas’ layout.

Phonetic

The Arabic Phonetic Keyboard simply maps the QWERTY layout to Arabic letters, based on their sound. Thus Q becomes ق, Y becomes ي and so on. It claims to be optimized for writing vowelized texts, especially Quranic Arabic, and thus includes quite a few combining characters and special symbols. Although it claims to make frequently used letters easily available – based on the work of Intellaren – it makes no effort to arrange letters according to their usage frequency.

Intellark

While technically speaking not a layout but alternative input method, Intellark by Intellaren is worth mentioning. It is based on repeatedly pressing the same button to modifiy the current character. For example pressing A on the QWERTY keyboard cycles through the alternatives ا أ إ آ and ء. Obviously this is slow, error-prone and violates Dvorak’s guidelines for keyboard layout designs.

Acknowledgements

This work would not have been possible without Martin Krzywinski’s work on carpalx. Neo Layout’s kbdneo2 Windows driver proved to be an invaluable source for understanding the undocumented nature of Windows keyboard driver development.