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NWG/RFC #373                                       14 July 1972NIC 11058                                          SU-AI                        ARBITRARY CHARACTER SETS                            by John McCarthyIt would be nice to be able to have documents stored in computers thatcould include arbitrary characters and to be able to display them onany CRT screen, edit them using any keyboard, and print them on anyprinter.  The object of this memorandum is to suggest how to get therefrom here with special reference to the ARPA network.Where are we now?   (1) At present, there is 96 character ASCII, and everyone agrees that   it should be included in any larger set.   (2) Many installations are dependent on 64 character sets which do not   even include the lower case latin alphabet.   (3) At the Stanford Artificial Intelligence Laboratory, we have a 114   character set that includes 96 character ASCII and which is   implemented in our keyboards, displays, and line printer   (4) Printers are becoming available that get their character designs   out of memory, for example, the Xerox XGP printer, one of which we are   getting.   (5) The IMLAC type display has the character designs in main memory so   that changing the displayed set is just a matter of reloading the   memory.   (6) Many display systems share the character generator among many   display units.  In some of these, e.g. the Datadisc, arbitrary sets   are probably feasible (using kludgery to be described later), but in   other systems, e.g. our III's arbitrary sets are not feasible.One possible approach to communication in expanded character sets isto produce an expanded standard set of characters, perhaps using 8 or9 bits and expect new equipment to implement this set.This approachhas the disadvantage that it will be very hard to get agreement onwhat the next step should be, and even if formal agreement isrealized, many groups will find it in their interest to ignore thestandard.                                                                [Page 1]

NWG/RFC# 373                        JMC 14-JUL-72 12:41  11058ARBITRARY CHARACTER SETS  by John McCarthyTherefore, I would like to suggest that the next step be to arbitrarycharacter sets.  I suggest implementing this in the following way:   (1) There be established a registry of characters.  Anyone can   register a new character.  Each character has a unique number, 17 bits   should be enough even to include Chinese.  Besides this, each   character has a name in ASCII usually mnemonic.  Finally, the   character has a design which is a picture on a 50 by 50 dot matrix.   (2) Besides the registry of characters, there is a registry of   characters sets, which different groups are using for different   classes of documents.  A registered character set has a registry   number and a table giving the correspondence between the character   codes as bit sequences and the registered character numbers.   (3) Associated with a document is a statement of the character code   used therein.  This may be one of the registered codes or it may   contain in addition modifications described by an auxiliary table   giving the code correspondence with registered character numbers.  A   character code may have an escape character that says that the next   character is described by its registry number.  The statement of the   character code may be a header on the document or the receiver may   have to learn it by some other means, e.g.  because its library   catalog entry contains this information.   (4) Devices such as printers and displays draw characters in different   ways and standardization doesn't seem feasible at present. Therefore,   it is necessary to provide a way of going from the standard   description of a character using a 50 by 50 dot matrix to whatever   method the device uses.  This is up to the programmers who are   supporting the device.  Some may choose to manually create files   describing how registered characters are implemented.  They may find   it too much work to provide for all the characters and to update their   files when new characters are registered.  Others will provide   programs for going from the registered descriptions to descriptions   compatible with their implementations.  Perhaps most will hand tailor   the characters most used and provide a program for the others.                                                                [Page 2]

NWG/RFC# 373                        JMC 14-JUL-72 12:41  11058ARBITRARY CHARACTER SETS  by John McCarthy   (5) The easiest device to handle is the line printer because it is   slow.  At the beginning of the print job, the SPOOL program will look   up the character set and load the printer's memory with the character   designs used in the particular document.  Sometimes, it may have to go   through the network to one of the computers that stores the registry   in order to find out what to do.   (6) Display systems that have a character memory for each display unit   can be handled in about the same way.  Users will occasionally   experience delays when the display programs are surprised by   unfamiliar characters.   (7) Display systems that share character memories require more   complicated treatment.  The object is to keep the memory large enough   to keep all the characters that the current set of users is using and   to handle the required table lookups from the different character   codes in a nice way.  There will be limitations on the diversity of   character sets that can be in use simultaneously. Systems like the   Datadisc that only look up the character when it is first written can   be extended to work with large sets.  Systems that have to look up   each character code 30 times per second in order to maintain the   display won't work so well.I have no special ideas about how to make keyboards adaptable toarbitrary sets.  Each user may have to fend for himself.In this memorandum so far, I have ignored typography, i.e. the factthat in printed documents the same letter may be printed in manyfonts.  Perhaps, each character in each font will require a separateregistered description, but with a constant difference between thenumbers of the same character in different fonts.  Installations willagain have to decide what font distinctions they will implement.Some other issues that might be considered are whether means can beprovided to adapt texts automatically to the line and page lengths ofthe different devices.It seems to me most likely that the typographical problems cannot besolved at this time, and it would be best to adopt conventions forregistering character designs at this time, and leave typography forlater.                                                                [Page 3]

NWG/RFC# 373                        JMC 14-JUL-72 12:41  11058ARBITRARY CHARACTER SETS  by John McCarthyIn my opinion, there is no real obstacle to establishing the registryin the ARPA network now, getting the standards organization to work,and being able to exchange documents in extended character sets assoon as the various installations can acquire the printers and displaydevices.It is the present policy of the Stanford Artificial IntelligenceLaboratory to acquire no more devices that are wedded to fixedcharacter sets.       [ This RFC was put into machine readable form for entry ]       [ into the online RFC archives by BBN Corp. under the   ]       [ direction of Alex McKenzie.                      1/97 ]                                                                [Page 4]