character set in programming
[0]
A character set refers to the composite number of different characters that
are being used and supported by a computer software and hardware. It consists
of codes, bit pattern or natural numbers used in defining some particular
character.
[1]
A character set is a set of symbols and encodings. A collation is a set of
rules for comparing characters in a character set. Let's make the distinction
clear with an example of an imaginary character set.
Suppose that we have an alphabet with four letters: 'A', 'B', 'a', 'b'. We
give each letter a number: 'A' = 0, 'B' = 1, 'a' = 2, 'b' = 3. The letter 'A'
is a symbol, the number 0 is the encoding for 'A', and the combination of all
four letters and their encodings is a character set.
Now, suppose that we want to compare two string values, 'A' and 'B'. The
simplest way to do this is to look at the encodings: 0 for 'A' and 1 for 'B'.
Because 0 is less than 1, we say 'A' is less than 'B'. Now, what we've just
done is apply a collation to our character set. The collation is a set of
rules (only one rule in this case): "compare the encodings." We call this
simplest of all possible collations a binary collation.
But what if we want to say that the lowercase and uppercase letters are
equivalent? Then we would have at least two rules: (1) treat the lowercase
letters 'a' and 'b' as equivalent to 'A' and 'B'; (2) then compare the
encodings. We call this a case-insensitive collation. It's a little more
complex than a binary collation.
In real life, most character sets have many characters: not just 'A' and 'B'
but whole alphabets, sometimes multiple alphabets or eastern writing systems
with thousands of characters, along with many special symbols and punctuation
marks. Also in real life, most collations have many rules: not just case
insensitivity but also accent insensitivity(an "accent" is a mark attached to
a character as in German 'ö') and multiple-character mappings (such as the
rule that 'ö' = 'OE' in one of the two German collations).