SUST Journal of Science and Technology, Vol. 21, No. 1, 2014; P: 47-56 Extended Bangla Keyboard (Submitted: August 28, 2010; Accepted for Publication: January 21, 2014) M. R. Selim Department of Computer Science & Engineering, Shahjalal University of Science & Technology, Bangladesh E-mail: [email protected] Abstract Bangla language has a big size character set. To fit all the characters within the existing keyboards, all the Bangla fixed keyboard layouts use several typing layers. Since using characters of a non-default typing layer requires pressing an extra key, it slows down the overall typing speed significantly. In this paper, to reduce the effect of multilayer typing, we propose to add some extra keys in the keyboards used by the Bangla language users. We show quantitatively the efficiency improvement of using such extended keyboards using various metrics. The metrics make use of the character frequency statistics derived from a corpus consisting of more than 250 million Bangla words. Our analysis shows that it is possible to save more than 8% keystrokes and 20% typing time and finger movements by adding only 6 extra keys in the currently used Bijoy keyboard. Keywords: Keyboard layout, Keystrokes, Typing time, Finger travelling distance, Bangla input method, Visual layout, Mechanical layout. 1. Introduction Most of the languages in the world including English have small size alphabets. On the other hand size of the Bangla alphabet is relatively big. About 300 unique characters are used in Bangla language [1]. Among them 39 consonants and 11 vowels are in graphic form. Besides, it has 3 (mostly used) consonants (য-ফলা, র-ফলা, েরফ) and 10 vowels in allographic (called কা’র) form [1]. These vowels and consonants and some most frequently used punctuation characters are assigned to different keys in a keyboard. Since their number is big, at least three typing layers are used in traditional (also called fixed ) layouts. The multilayer typing has an adverse effect on the efficiency. It slows down a typist significantly. The main goal of any typist is to type as fast as possible. How fast a typist can type depends on few design factors. One of them is the number of keys in keyboard. Currently used computer keyboards were originated from the type writer keyboards which were designed for English language. The number of keys in keyboards is sufficient for English but not for Bangla language. Therefore, adding several extra keys on the keyboard can notably increase the typing efficiency. In this paper, we propose to add few extra keys in the keyboards for Bangla language and analyze the effect of extra keys on the efficiency. We call such a keyboard, which has few extra keys, the extended Bangla keyboard. Adding extra keys in keyboard for specific purposes is not new. The current form of the keyboards has undergone many changes. The first computer terminals such as the Teletype used the typewriter’s QWERTY layouts with few added keys, e.g., escape (Esc). Later keyboards added function keys and arrow keys. After the 1980s, most full-sized computer keyboards have followed a standard which have added many new keys such as separate numeric keypad, 12 function keys across the top, and cursor movement keys. Most new PC keyboards now have 104 or 105 keys, with the addition of two Windows keys and a menu key [7]. Laptop keyboards often add Fn modifier keys. Multimedia keyboards use several additional keys. Besides non-alphabetic keys, alphabetic keys are also added for different characters in different languages. For example, for Korean (Hangul), Hungarian and Japanese languages, at least two new alphabetic keys have been added or old punctuation keys have been replaced [8]. Moreover, for Japanese language three and for Korean language two more new keys have been added in the bottom row for typing- mode switching functions [8]. This work is the first attempt to propose keyboard extension and analyze the effect of addition of extra keys in 48 Md. Reza Selim Bangla keyboards. Previous attempts [2][3] were made only to design visual layouts to improve the typing efficiency. Once it is accepted that new keys should be added, how the characters will be distributed over the keys, i.e., what the visual layout should be is a different subject of research which strives for urgent attention of the researchers. However, scope of this paper is to answer the questions like ‘Why should we add extra keys to Bangla keyboards?’ ‘How much typing efficiency will be improved if extra keys are added?’ The rest of the paper is organized as follows. Section II clarifies why such an extended keyboard is necessary, section III explains where to add the new keys, section IV analyzes the efficiency improvement and finally section V concludes our work. 2. Why Extended Keyboard In English text, the frequency of uppercase letters is less than 6% [5]. That is, a typist typing English text remains more than 94% times on default typing layer. On the other hand, if we assume that a Bangla keyboard layout assigns the most frequently used 26 letters on the default layer (ergonomically, this is not a good way to design keyboard layout), it comprises about 87% of relative character frequencies [1]. Therefore, at least 13% time a Bangla typist has to remain on non-default layers. The effect of the typing layers on typing efficiency is very big. For example, in Shift typing layer, the Shift key must be kept pressed while the key for a Bangla character is pressed. Since Shift key is pressed by the slowest, weakest and the smallest finger, it takes much time and decrease the overall efficiency. The efficiency even aggravates, if the target character is on a key under the little fingers’ range. It means that, the more frequently we use a key of a non-default layer, the more it reduces the typing speed. Therefore, minimizing the use of non-default typing layer is desirable. It is obvious that, designing an efficient visual layout for Bangla keyboard cannot solve this problem of inefficiency. Because, as we have explained, at least 13% key strokes must be on non-default layers. One simple but effective solution is, as we propose in this paper, to increase the number of alphabetic keys in Bangla keyboards. 3. The Extended Keyboard In the extended keyboard, where to place the additional keys is an important issue. In the currently used keyboards, there is no space within the range of index, middle and ring fingers for new keys. Therefore, any new key should be added within the range of thumb or little fingers. The two thumb fingers are the strongest and most flexible of all fingers and have the back-up of a considerably larger section of the brain than other fingers [4[[6]. Experiment also shows that each thumb finger can easily access up to 8 or 9 keys [6][9]. Thumb fingers are already used extensively to access many keys in ergonometric keyboard layout Maltron Mark [6]. Besides, use of space bar and hence the use of thumb fingers in typing Bangla text is less compared to most of the languages in the world. This is because word length in Bangla is larger than most other languages [11]. For example, in Brown Corpus, the average size of an English word is 4.26 [15], whereas for Bangla it is nearly 5 characters. These are the reasons that thumb fingers can and should be used to type not only the spaces but also other letters. Fig. 1: JIS Keyboard. Dark Gray Keys are Additional Keys Compared to Common ISO Keyboard. In the bottom row of the keyboard, the size of the space bar can be reduced and at least three new keys can be accommodated. For example, in JIS (Japanese Industry Standard) keyboard three and in Korean language keyboards two extra keys have been added at the bottom row in this way [8]. In the current keyboards, space bar is assigned to both of the right and left thumbs. We propose here that the newly added keys in the bottom row should be under the Extended Bangla Keyboard 49 thumb fingers range. The home position of a thumb should be one of the new keys. But another thumb should rest on the space bar. Practically, for current keyboards, almost all the time, only one thumb finger is used by the typist to type the space character. Therefore, it is rationale to use one thumb finger to type spaces always. Several more keys can be added under the little fingers of either or both hands. These keys can be added by reducing the size of the Shift, Enter and Backspace keys. In Japanese keyboards, two more extra keys have been added in this way [8]. Fig. 1 shows the Japanese keyboard (JIS standard) with 5 additional keys compared to common ISO keyboard [8]. It is obvious that since hardware modification is required to add new keys, our proposed scheme is not possible to implement on the existing Bangla keyboards. In fact, this analysis targets not to improve the existing keyboards but to promote starting an initiative to build a new keyboard standard, like JIS mechanical layout [8], which can be applied on the newly manufactured keyboards. However, someone can use this analysis technique for the existing keyboards also in one of the two ways. The existing keyboards contain some duplicate keys, e.g., Ctrl, Alt, Win and Shift keys. Most of the typists usually use only one of every pair of duplicate keys. This is especially true for Ctrl, Alt and Win keys. These unused keys can easily be used for typing Bnagla characters so that the effect of multilayer typing is reduced.