NWG/RFC #373 14 July 1972
NIC 11058 SU-AI
ARBITRARY CHARACTER SETS 1
by John McCarthy 2
3
It would be nice to be able to have documents stored in
computers that could include arbitrary characters and to be
able to display them on any CRT screen, edit them using any
keyboard, and print them on any printer. The object of this
memorandum is to suggest how to get there from here with
special reference to the ARPA network. 4
Where are we now? 5
(1) At present, there is 96 character ASCII, and everyone
agrees that it should be included in any larger set. 5a
(2) Many installations are dependent on 64 character sets
which do not even include the lower case latin alphabet. 5b
(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. 5c
(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. 5d
(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. 5e
(6) Many display systems share the character generator among
arbitrary 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. 5f
One possible approach to communication in expanded character
sets is to produce an expanded standard set of characters,
perhaps using 8 or 9 bits and expect new equipment to implement
this set. This approach has the disadvantage that it will be
very hard to get agreement on what the next step should be, and
even if formal agreement is realized, many groups will find it
in their interests to ignore the standard. 6
1
NWG/RFC# 373 JMC 14-JUL-72 12:41 11058
ARBITRARY CHARACTER SETS by John McCarthy
Therefore, I would like to suggest that the next step be to
arbitrary character sets. I suggest implementing this in the
following way: 7
(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. 7a
(2) Besides the registry of characters, there is a registry
of character 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. 7b
(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. 7c
(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. 7d
2
NWG/RFC# 373 JMC 14-JUL-72 12:41 11058
ARBITRARY 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. 7e
(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. 7f
(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. 7g
I have no special ideas about how to make keyboards adaptable
to arbitrary sets. Each user may have to fend for himself. 8
In this memorandum so far, I have ignored typography, i.e. the
fact that in printed documents the same letter may be printed
in many fonts. Perhaps, each character in each font will
require a separate registered description, but with a constant
difference between the numbers of the same character in
different fonts. Installations will again have to decide what
font distinctions they will implement. 9
Some other issues that might be considered are whether means
can be provided to adapt texts automatically to the line and
page lengths of the different devices. 10
It seems to me mosts likely that the typographical problems
cannot be solved at this time, and it would be best to adopt
conventions for registering character designs at this time, and
leave typography for later. 11
3
NWG/RFC# 373 JMC 14-JUL-72 12:41 11058
ARBITRARY CHARACTER SETS by John McCarthy
In my opinion, there is no real obstacle to establishing the
registry in the ARPA network now, getting the standards
organizations to work, and being able to exchange documents in
extended character sets as soon as the various installations
can acquire the printers and display devices. 12
It is the present policy of the Stanford Artificial
Intelligence Laboratory to acquire no more devices that are
wedded to fixed character sets 13
4
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