The following summaries use very
language, and they are hardly understandable in isolation. However,
having read the text of this chapter, you may find them useful and
return to them later. The terminology
quite a lot, so the summaries help in checking out how this book
1.10.1. Summary of
Following is a list of terms you may come
A basic unit of textual information, as abstract
concept, as opposed to stylistic and typographic variation between
that can be identified as the same character.
A mapping, often presented in tabular form, that
defines a one-to-one correspondence between characters in a
and a set of nonnegative integers.
A method (algorithm) for presenting characters
in digital form by mapping sequences of code
into sequences of octets. Encodings have names, which can be
Figure 1-26. Menu of contexts for font
settings in a version of Firefox
The integer assigned to a character in a
character code. Synonyms: code position, code value, code element,
code point, code set value, code.
A collection of distinct characters. No specific
internal presentation in computers or data transfer is assumed. The
repertoire per se does not even define an ordering for the
characters; ordering for sorting and other purposes is to be
specified separately. A character repertoire is usually defined by
specifying names of characters and a sample (or reference)
presentation of characters in visible form.
A basic unit of visual rendering of
charactersi.e., a particular visible presentation of a character,
or part of character, or pair or sequence of characters.
A sequence of eight binary digits (0 and 1)
treated as a unit.
1.10.2. Summary of
We can consider a character, say @, at different
conceptual levels, or levels of abstraction:
Character as an
The idea of a particular character, in the mind
of an individual and in social usage. For example, whatever @
suggests to you, or your
, or people in your country.
defined in a specification
A particular definition of a character, aimed at
making the idea explicit and communicable. The definition can show
some glyph(s) for the character,
it (e.g., "commercial at"),
describe it verbally, and list its properties in some general
A character as defined in a specification
together with its code number in some system of such numbers. In
most systems, the number of @ is 40 in hexadecimal. The number can
be used as a concise way of referring to the characters, often
using some special notation like 0x40 or U+0040.
A particular internal representation of the code
number of a character, and hence of the character. This depends on
the encoding used. For the @ character, the representation could be
the octet 40 (hex) alonei.e., the bit sequence 00001000. In another
encoding, however, it could consist of two octets, 00 and 40.
A rendering of a charactere.g., @ or @ or @.