NRSI: Computers & Writing Systems
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Implementing Writing Systems (The Book)
Table of Contents
The NRSI Model for Implementing
Writing Systems
Over its short history, the Non-Roman Script Initiative of SIL International has developed a model for using
computers to implement the various writing systems that are needed for text input, storage, processing, and
output.
Understanding characters,
keystrokes, codepoints and glyphs
Software systems that are used for working with multilingual data are evolving, and it is increasingly
important for users and support personnel to have an understanding of how these systems work. This chapter
explains some of the most basic concepts involved in working with multilingual text; characters, keystrokes,
codepoints, and glyphs. Each notion is explained, as is the way they relate to one another and interact
within a computer system.
Character set encoding
basics
In understanding technologies for working with multilingual and multi-script text data, we need to start with
an understanding of character encoding. Systems for working with text involve a collection of processes that
work together—processes for creating and editing text, presenting it, for sorting, for laying out paragraphs
and wrapping at line breaks, etc. Character encoding is the thing that ties all of these processes
together.
Computer systems employ a wide variety of character encodings. The most important of these for us is Unicode.
It is also important for us to understand other encodings, however, and how they relate to Unicode. In this
section, I want to look at some basic concepts that relate to all encodings, and also give an overview of
legacy encodings and their importance for us.
Understanding Unicode™ -
I
Unicode is a hot topic these days among computer users that work with multilingual text. They know it is
important, and they hear it will solve problems, especially for dealing with text involving multiple scripts.
They may not know where to go to learn about it, though. Or they may have read a few things about it and
perhaps have seen some code charts, but they are at a point at which they need to gain a firmer understanding
so that they can start to develop implementations or create content. This introduction is intended to give
such people the basic grounding that they need.
Understanding Unicode™ -
II
Unicode is a hot topic these days among computer users that work with multilingual text. They know it is
important, and they hear it will solve problems, especially for dealing with text involving multiple scripts.
They may not know where to go to learn about it, though. Or they may have read a few things about it and
perhaps have seen some code charts, but they are at a point at which they need to gain a firmer understanding
so that they can start to develop implementations or create content. This introduction is intended to give
such people the basic grounding that they need.
An introduction to keyboard design
theory: What goes where?
Designing a keyboard is relatively easy: you just allocate codepoints to keystrokes. The difficulty comes
when trying to decide what codepoints to assign to what keystrokes. Do you design based around the characters
on the keytops of a user's keyboard or the relative position of the keys? What do you do if you want to be
able to type more characters than there are keys in your keyboard?
Guidelines for Writing System Support: Technical Details: Smart Rendering: Part 3
Rendering technologies
overview
A tour of basic issues related to rendering text for various writing systems, beginning with a simple model
and building up to current technologies available for complex rendering.
An Introduction to TrueType Fonts:
A look inside the TTF format
The primary font technology used on Microsoft Windows and the Mac OS is based on the TrueType specification.
This article examines the function of each of the internal tables that comprise a TrueType font.
Challenges in publishing with
non-Roman scripts
There are a number of challenges in the typesetting of non-Roman scripts. These include problems of
interaction between the font and typesetting system, problems of very large character sets, and
considerations of typesetting the particular script.
Mapping codepoints to Unicode
encoding forms
This appendix describes in detail the mappings from Unicode codepoints to the code unit sequences used in
each encoding form.
A review of characters with
compatibility decompositions
This appendix is intended, therefore, to provide an introduction to this set of characters, which constitute
perhaps the least principled elements of the Standard.
TrueType table listing
This is a list of the tables used in TrueType files. Also included are tables added by OpenType, Graphite,
and Apple.
Glossary
A glossary of terms associated with implementing writing systems compiled by the NRSI.
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