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Bi-directional Typing Interfaces

To allow for bi-directional text entry from a keyboard, the interfaces must be able to intercept and process each keystroke. These interfaces can be part of the terminal and associated controller’s hardware or micro code, or they can be a specific routine that is added to the operating system. There are two typing interfaces to consider:

Manual typing method

Automatic (logical) typing method.

Manual Typing Method

In the manual typing method the user informs the system in which direction the characters are to be typed. For mixed-direction typing, the user makes extensive use of the Push and End Push keyboard functions.

The manual method also supports an Automatic Push (Auto Push) mode. When the Auto Push setting is active, the Push Mode is started and terminated automatically, according to the actual characters being typed.

When the manual typing method is active, the keyboard language group and cursor direction are handled separately by the system. This means that the user has separate control for:

The direction of the field – controlled by the Field Reverse keyboard function.

The direction of the typed text – controlled by the Push and End Push keyboard functions.

The keyboard language group – controlled by the keyboard language group switching keys.

Automatic (Logical) Typing Method

This convention provides some automatic handling of directionality. When this method is active, the system determines the directionality of each part of the text (each segment) based on the actual characters being typed, using a set of predefined rules.

The method is called logical because the direction of the text is logically deduced based on the language of the characters.

With this method, the system automatically determines how to display characters in the correct order when the user switches keyboard language groups.

Another feature of this method is that it handles text in typing order; that is, the system remembers the order in which the characters were initially typed. It then uses this knowledge along with a set of predefined rules, to determine how the text is displayed, processed and deleted by the application.

If the cursor is in the Home position (the first logical position in the field or window) and a character of a language other than the default language of the current orientation is entered, the screen or window orientation is reversed automatically. That is, if the character entered is Hebrew, the window orientation is right-to-left; if the character is English, the window orientation is left-to-right.

Common User Access and Bi-directional Languages

The basic rule for applications that are to conform to Common User Access guidelines is that “… All pieces of data must be displayed in the orientation that is correct for the application user. Data input must be supported in the orientation that is natural for users”.

Thai Language and its Writing System

The Thai language is representative of a class of complex-text languages whose characters are composed of a number of symbols or elements. Thai belongs to the Sino-Tibetan family of languages. Like the Chinese languages, which also belong to this family, Thai is a monosyllabic tone language. While it resembles Chinese structurally and though much of its basic vocabulary is of Chinese origin, it has also been greatly influenced by both Pali and Sanskrit.

The Thai writing system was developed from the Devanagari system, which originated in India and came to Thailand from Cambodia. A major difference between the Chinese and Thai writing systems is that while Chinese makes use of a large number of pictorial symbols, Thai uses an alphabet of consonants, vowels, tone marks, diacritics and special symbols. With some exceptions, a Thai word can be pronounced correctly on sight, in a similar manner to Italian or French.

Writing Thai Characters – Graphic Representation

Thai is written from left to right, without spaces between words. Each word is represented by one or more syllables; each syllable consists of a consonant, a vowel, a tone and a final consonant or a final diacritic. Spaces in the text indicate the ends of phrases or sentences, and are thus used as a form of punctuation. Thus, individual words are recognized only by scanning the text for syllable boundaries. Compared to western writing systems, the composed characters tend to be taller and thinner.

A line of Thai text can be considered to be logically divided into four parallel lines:

The base line, on which consonants, some vowels, some Thai symbols and Thai numbers are written

The line below the base line, used for writing lower vowels and lower diacritics

The line above the base line, used for writing upper vowels and upper diacritics

The line above the upper vowel line, used for writing tone marks and upper diacritics. (If there is no upper vowel, the tone mark or the upper diacritic is written on the upper vowel line.)

Thai Written Symbols

Generally speaking, the more than 2,000 characters in the Thai writing system can be categorised into 20 types of written symbols, with 88 basic symbols:

10 base line numerics

44 base line consonants

3 base line ancient signs

2 base line special symbols

1 base line currency sign

1 base line Thai word break character

5 base line leading vowels (vowel in front of consonant)

3 base line type 1 following vowels

1 base line type 2 following vowels

2 base line type 3 following vowels

1 upper vowel line type 1 upper vowel

2 upper vowel line type 2 upper vowel

2 upper vowel line type 3 upper vowel

1 upper vowel line ancient sign (or upper vowel line type 3 upper diacritic)

4 tone mark line tone marks

2 tone mark line type 1 upper diacritic symbol

1-tone mark line type 2 upper diacritic symbols

1 lower vowel line type 1 lower vowel

1 lower vowel line type 2 lower vowel

1 lower vowel line lower diacritic symbol

Normally, Thai data is encoded using a single-byte code page, where each symbol has an adequate code point. The symbols are used to enter Thai data on a Thai keyboard. Thus the Thai data is stored, for processing purposes, as symbol elements.

These elements have to be combined into characters for rendering purposes.

Writing Order

In the most common writing order, first a base line symbol is written, and then optionally, an upper vowel or lower vowel symbol is written above or below it. A tone mark symbol may then optionally be written either above the base line symbol, or above the upper vowel symbol, if present.

This order of writing is taught in Thai elementary schools. However, writing-order inconsistencies exist between individuals. The valid combinations of symbols for Thai composed characters are:

Base line consonant symbol

Base line consonant symbol and tone mark symbol

Base line consonant symbol and upper diacritic symbol

Base line consonant symbol and upper vowel symbol

Base line consonant symbol, upper vowel symbol and tone mark symbol

Base line consonant symbol, upper vowel symbol and upper diacritic symbol

Base line consonant symbol and lower vowel symbol

Base line consonant symbol and lower diacritic symbol

Base line consonant symbol, lower vowel symbol and tone mark symbol.

Any other combinations would be considered invalid.

What is a Thai Character?

From a linguistic or phonetic point of view, the Thai writing system is actually more complex than that described above.

Consonants are written on the base line. A middle vowel can be written either before, after or straddling the related consonant.

Upper-vowels are written above, and lower vowels below, their related consonant. Vowels are always pronounced and collated after the consonant. The tone mark is usually written after the upper vowel or lower vowel, but some people might write it after the consonant. The left and right pieces of a middle vowel, which straddle a consonant, are included as separate components in some encoding schemes.

To prevent confusion, the term-composed character is used here for the representation of one syllable at a writing position, and the term symbol is used for the components of a composed character.

Thai Numbers

Although Western numerals (Arabic numbers) are now widely used in Thai writing, there are also ten Thai glyphs for numbers.

In Thai, the equivalent of the Arabic digits 1, 2, 3, 4, 5, 6, 7, 8, 9 and 0 are respectively:

Figure: Shape of the National Numbers in Thai

Character Composition

According to the rules for writing Thai, only certain combinations of symbols are possible. When someone fluent in Thai is writing or reading a line, a process of composition is taking place. In about 74 percent of cases a character is formed from a single symbol; in about 22 percent of cases, it is formed from two symbols; and in 4 percent of cases it is formed from three symbols.

A Thai speaker does not think of a composed character as, for example, an accented character in French. This difference in thinking is reflected in the difference between European and Thai keyboards. In European keyboards, dead keys are used to place accents on characters. The dead key is pressed first to show the accent, and then the character key is pressed. The cursor moves only after the character has been entered. All character manipulation is done at the cursor position.

In Thai the consonant or middle vowel is entered first. It is displayed, and the cursor then moves one position to the right. The upper and lower (dead key) vowels and tone marks are then added to the character to the left of the cursor. The rightmost column of positions on the screen is used to display the cursor only, and data is not allowed in this column. Usually vowels and tone marks are stacked on the consonants to compose syllables. The exception is middle vowels, which stay independently at the same level as the consonants.

Thai Character Rendering

Quality font rendering (for example, for desktop publishing), requires additional changes to be made to a Thai composite character form, and sometimes to other characters in its vicinity.


Some of the base line symbols that have a descender in the lower position change shape in the presence of a lower vowel.

Some other base line symbols with a descender do not change their shape. Instead, when these symbols are combined with a lower vowel, the vertical or horizontal position of that lower vowel is changed. Similarly, when some base line symbols with an ascender are combined with an upper vowel, a tone mark or both, the location of the upper vowel, tone mark or both is shifted horizontally.

The vertical position of a tone mark is dependent upon the presence or absence of an upper vowel. If an upper vowel is not present, the tone mark is positioned at the level that an upper vowel would occupy.

A specific base line vowel partially overlaps with the associated previous consonant. If the associated consonant does not have an ascender, the vowel is moved up and to the left, to hang over the right side of the previous base line consonant. If the associated consonant has an ascender, the vowel is split into two pieces, with one piece positioned to the left of the ascender and another to the right.

It is thus possible to recognize a similarity between character composition in Thai, and ligatures composition and shaping in bi-directional languages. The character presented is not identical with the symbols stored, so a shaping or composing algorithm must be applied.

Similarly, there are cases where the shaping transformation must not to be performed at rendering, but at a previous stage. When using the high-quality printers adapted for double-byte character set (DBCS), a shaping of characters (maximum three-symbol), is performed as part of the transformation of text to a double-byte encoding scheme. In this case, the text can be considered stored in a shaped form for higher-efficiency printing. This resembles the case in which Arabic message text is kept in storage in a shaped layout.

Conclusions and Guidelines

Though so different in their appearances, all complex-text languages – the bi-directional ones such as Arabic, Farsi, Urdu, Hebrew and Yiddish, or the languages such as Thai, Lao, or Korean – have a distinct common characteristic: the form of the rendered text is different from that of the stored text. The transformation functions needed to perform the changes between rendered and stored text depend on descriptive information pertaining to the attributes of complex-text languages: global orientation, text-type, symmetrical swapping, shaping and national numbers.

Application developers should be aware of the fact that in the complex-text languages there is a need for transformations between the different text layouts. They should allow for user or system exits to facilitate invoking these transformations, in those places where a transformation might be expected (at input, before output, before a collating process, and so on). Programs must be able to identify the location and content of the complex-text attributes, and be able to change their content if needed.

Just as for any other language, an application meant to be used for complex-text languages should utilize the appropriate language code page and cultural data (date and time layout, collating sequence, monetary layout, and so on).

Application developers should design their products in such a way that they use, as much as possible, the standard functions and controls provided by the operating system services or toolkits for these languages. They might choose to use the APIs offered in the national language versions of the operating system services or toolkits to perform such transformations (when available).

It would be good practice to concentrate all the functions related to National Language in a specific program area for easy maintainability and change support.


1.Arabic is spoken mainly in Algeria, Bahrain, Egypt, Iraq, Israel, Jordan, Kuwait, Lebanon, Libya, Morocco, Oman, Qatar, Saudi Arabia, Sudan, Syria, Tunisia, United Arab Emirates, and Yemen. Urdu is spoken mainly in Pakistan. Farsi is spoken mainly in Iran. Hebrew is spoken mainly in Israel, and Yiddish is spoken mainly in Israel, Europe, and North America.

2.Sometimes it is possible to have a contextual global orientation, where the global orientation is set according to the directional characteristic of the first character in the data stream that has a distinct directionality.

3.Legacy applications are those that have been inherited from a prior era. They may be obsolete, but must be supported.

4.The Basic Display Algorithm was initially published in the Directionality Appendix A of the Unicode standard.

5.Other complex-text languages that have their own national glyphs for decimal digits are Devanagari, Gurmukhi, Gujarati, Oriya, Bengali, Tamil, Telugu, Malayalam, Sinhalese, Khmer (Cambodian), Lao, Mongolian, Chinese, Tibetan and Thai.


Writing Systems

The Blackwell Encyclopedia of Writing Systems defines a writing system as “a set of visible or tactile signs used to represent units of language in a systematic way”. This simple explanation encompasses a huge spectrum of writing systems with vastly different stylistic and structural characteristics spanning across many regions of this planet.

Writing provides a way of extending human memory by imprinting into media less fickle than the human brain. However, many early philosophers, such as Plato, have branded writing as a detriment to the human intellect. They argued that it makes the brain lazy and decreases the capacity of memory. It is true that many non-writing cultures often pass long poems and proses from generation to generation without any change, and writing cultures can’t seem to do that. But writing was a very useful invention for complex and high-population cultures.

Writing was used for record keeping to correctly counting agricultural products, for keeping the calendar to plant crops at the correct time. And writing was used for religious purpose (divination and communicating with the supernatural world) and socio-political functions (reinforcing the kingship).

However, writing isn’t an absolute requirement of urban culture. In past centuries, scientists had used writing as one of the “signs” of civilization, which is an incorrect assumption. The Incas and earlier Andean civilizations never developed a writing system. They, in turn, came up with interesting solutions: they used the quips (a series of ropes with knots indicating amounts) for record keeping, and complex tapestries as calendars. The Mississipians who built Cahokia didn’t seem to have used any kind of record keeping at all, but they built very impressive cities in the American Midwest.

Because writing is so intricate there has been many theories concerning the origins of writing.

Writing systems differ structure, stylistically, familiarly, geographically, and so on. Here’s the several ways I categorize them:

Types: Classification according to how the system works.

Families: Classification according to “genetic” relations.

Regions: Classification according to geographical regions.

A to Z: Alphabetical listing of scripts, just for your convenience.

The study of writing systems is a very broad field, and I cannot claim that this website will reveal every detail. Far from it, in fact. I think I only cover 10% of all writing systems of the world. There are many good books out there, and you can start in my Bibliography section.

Created March 19, 2000

Mythological Origins

Among many ancient societies, writing held a extremely special and important roll. Often writing is so revered that myths and deities were drawn up to explain its divine origin.

In ancient Egypt, for example, the invention of writing is attributed to the god Thoth or Tehuti (Dhwty in Egyptian), who was not only the scribe and historian of the gods but also kept the calendar and invented art and science. In some Egyptian myths, Thoth is also portrayed as the creator of speech and possessing the power to transform speech into material objects.

This ties in closely with the Egyptian belief that in order for a person to achieve immortality his or her name must be spoken or inscribed somewhere forever.

In Mesopotamia, among the Sumerians the god Enlil was the creator of writing. Later during Assyrian, and Babylonian periods, the god Nabu was credited as the inventor of writing and scribe of the gods. And similar to Thoth, Mesopotamian scribal gods also exhibit the power of creation via divine speech.

Among the Maya, the supreme deity Itzamna was a shaman and sorcerer as well as the creator of the world. (In fact, the root of his name, “itz”, can be roughly translated as “magical substance, usually secreted by some object, that sustains the gods”). Itzamna was also responsible for the creation of writing and time keeping. Strangely enough, though, Itzamna isn’t a scribal god. This duty falls on usually a pair of monkey gods as depicted on many Maya pots and is also preserved in the highland Maya epic “Popol Vuh”. Still, in one rare case, the scribe is a rabbit.

In China, the invention of writing was not attributed to a deity but instead to a legendary ancient sage named Fu Hsi, who also invented divination of the future by using turtle shells (hence the oracle bones). He’s also an amazing marketing guru too. Next time you visit a Chinese household, look up when you’re at the front door, and you might see a little circular mirror surrounded by eight multi-line symbols. These symbols (trig rams) are used to communicate with spirits, and together with the mirror they serve as evil repellent too. Just imagine how many of these have been sold in the past 4,000 years! Move over Bill Gates! If Fu Hsi had filed for patents he would have owned the whole world by now!

Ahem … anyway, in these ancient cultures, the creation and use of writing was closely tied to divine creative powers. By uttering or writing down a word, objects get created or people get immortal. They reinforced the notion of writing as supernatural and therefore enforced the exclusivity of the “scribe” class.

Monogenesis? Evolution?!

Okay, let’s jump ahead in time to the 19th century. Overzealous and Euro centric (I’m using euphemisms here), scholars held that writing was invented only once in Mesopotamia, and all subsequent writing systems were offshoot of this original. They claim that Chinese and Indus writing were evolved from Middle Eastern prototypes, and they completely treat Maya not as a writing system but as a purely calendrical and mnemonic system.

What’s worse is that they started abusing poor Darwin’s theory of evolution. They separate writing systems into functional types, which is okay and still scientific. But then they assigned “evolved-ness” to each group, with alphabet being the most evolved and inherently the best system. Logographic systems like Chinese are considered primitive, archaic, and much inferior, and syllabic systems fall somewhere in between. Their rationale is that alphabets have a small number of signs (easy on your memory) and allow the writer to specify every phonetic value in the language down to the most minute detail.

The biggest problem with this monogenesis and evolution of writing system is obviously that of culturally tinted views. It easily placed Europe as the pinnacle of civilization, relegated the rest of the world to the “primitive” and “unevolved” nature of all other continents of the world, and helped to justify Europe’s imperialistic age.

This whole thing started to crack when the evidence for the indigenous origin of Chinese became very strong with the discovery of the oracle bones and the lack of any earlier text in the vast space between the Iranian plateau and the Yellow River.

Modern Day Views

Nowadays there is more-or-less consensus on these points:

Writing was invented in parallel in at least three, or four, places: Mesopotamia, China, Mesoamerica, and possibly Indus. No type of writing system is superior or inferior to another, as the type is often dependent on the language they represent (unless it’s English). Writing system is not a marker of civilization, as many major urban culture did not employ (full evolved) writing such as the Incas.

The Rabbit Scribe

Rabbits have been the embodiment of different natural and human attributes. Sometimes they are seen as symbols of fertility (as they reproduce so quickly and in great numbers). Other times they are associated with the moon, as the gray patches on the moon to many cultures is a leaping rabbit. Yet some other time they are tricksters, helping the heroes of a story in defeating the bad guys.

But in a Classic Maya funerary vase from northern Guatemala, now in the Princeton University Art Museum, the rabbit was made into a scribal god! Among the Maya, divine scribes usually are monkeys. It is not known if there were any rabbit scribe gods among the Maya. The scene on the vase describes the ghastly rituals in the underworld. It may even be an illustrated chapter from the adventures of the Hero Twins (as recorded in the Quich? Maya holy book Popol Vuh). The rabbit sits below an important old god, perhaps diligently recording the human sacrifice happening in front of the old god in a jaguar-pelt bound codex. Or perhaps he’s doing something else…writing poetry, history, jokes, obscene stories?

Well, the rabbit god may have been some forgotten figure in Maya mythology. Or it may have been just a playful invention on the part of the painter of the vase. We just don’t know at this moment.

Transforming the Rabbit Scribe…

The following are two pictures of the same rabbit, the left one represent how he looks on a piece of paper as drawn by Michael Coe, while the right one is how he looks on Ancient Scripts’ main page.

The old rabbit, as I scanned it from a black-and-white drawing. Notice the background scene:

Somebody’s foot, and the dark band in the middle which is the raised floor of a house.

My updates to the scan…Added color, erased the background drawings, and enlarged his eye and moved it forward to make him look cuter.

Created Sept 5, 1997

Types of Writing Systems

Writing systems can be classified in “types” by the way they represent the underlying language. Note, however, that not every script neatly fits into each type.

Proto-Writing: This is the most rudimentary type of writing system. Examples of this type usually have small inventory of signs and large room for interpretation. They don’t denote full running texts but instead serve more like mnemonic devices for the reader.

However, they are writing systems because in some small way they do represent the underlying language, no matter how poorly. Naxi Mixtec

Logographic: A system of this kind uses a tremendous number of signs, each to represent a morpheme. A morpheme is the minimal unit in a language that carries some meaning. So, a logogram, a sign in a logographic system, may represent a word, or part of a word (like a suffix to denote a plural noun). Because of this, the number of signs could grow to staggering numbers like Chinese which has more than 10,000 signs (most of them unused in everyday usage).

Sumerian cuneiform


Indus (?)

Classic Yi



Logo-phonetic: This is sort of like stripped down versions of logographic systems. In essence, there are two types of signs, ones denoting morphemes and ones denoting sound. Most of the logo-phonetic are logo-syllabic, meaning that they denote syllables.

An exception is Egyptian, whose phonetic signs denote consonants. Akkadian/Assyrian cuneiform Hieroglyphic Luwian

La Mojarra


Zapotec (?)


Egyptian Hieroglyphs

Syllabic: In a syllabic writing system, the overwhelming number of signs are used solely for their phonetic values. A few non-phonetic are used for numbers, punctuation, and commonly used words.




Linear A

Linear B

Old Persian


Modern Yi

Byblos Script (?)

Consonantal Alphabetic: Vowels are not written in purely consonantal alphabets, which are descendents of Proto-Canaanite. “Alphabet” for this type of script is somewhat controversial, because you can also argue that it is a syllabic script where each sign consists of consonant and a vowel, but the vowel is not specified.


Berber and Tifinagh

Proto-Canaanite & Phoenician

South Arabian


Syllabic Alphabetic: South Asian scripts such as Brahmi and its descendents fit into both syllabary and alphabet. It is syllabic because the basic sign contains a consonant and a vowel. However, every sign has the same vowel, such as /a/ in Brahmi. To make syllables with a different vowel, you add special markings to the basic sign, which is somewhat like an alphabet. Hence the name “syllabic alphabet”.






C and V Alphabetic: Nearly all the sounds in a language can be represented by an appropriate consonant and vowel alphabet. However, just take a look at English spelling and you can almost feel we’re back to logographic systems !





Unknown: Sometimes it is possible to infer what type a script is by counting the number of signs it has. However, sometimes it is impossible because there isn?t enough textual evidence to establish what the type is. The most famous example of this is the Phaistos Disc.

What about ideographic?

You may have also encountered the term “ideographic”. What it describes is a writing system whose symbols represent ideas. So, any person speaking any language given that they know which symbol in the system represents which idea can read an ideographic writing system. However, the concept of an “ideographic” writing system does not apply to any known writing system. Every writing system in the world replicates a language, so it encodes sounds and grammatical rules. Even at the most primitive level, in writing systems like Naxi or Mixtec, where extremely pictorial signs consist of the main bulk of the system, tricks to spell names using the rebus principle can still be detected.

Futhermore, because of the nature of language, putting words together make more complex ideas. Since there are an infinite number of combinations of words, there clearly cannot be sufficient signs to represent each idea in a language. So, the writing system must mimick the natural language by putting two signs together to form a compound that represents the more complex idea. However, when this happens, signs don’t just get juxtaposed randomly, but instead in some predescribed way that follows the grammatical rule of the language. All of a sudden, this turns into a logographic system!

My point is that ideographic systems don’t exist. It is a myth. Any writing system starts off as logographic and grows from there.

This is, of course, just my opinion, but I feel that it rests relatively well on solid data from writing systems of the world

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