Unicode

Question 1

writing system/script

Answer 1

a system more or less permanent marks used to represent an utterance in such a way that it can be recovered without the intervention of an utterance

Question 2

character

Answer 2

the smallest component of a writing system that has a semantic value

Question 3

grapheme

Answer 3

the smallest sound unit in the spoken language

Question 4

glyphs

Answer 4

representation of a character as it is displayed (i.e. fonts)

Question 5

unicode

Answer 5

clear encoding to embrace all the world’s languages & is emerging as the gold standard

Question 6

design principles of Unicode

Answer 6

universality, efficiency, characters not glyphs, semantics, plain text, logical order, unification, dynamic composition, stability, convertibility

Question 7

surrogate pairs

Answer 7

an extension mechanism that consists of 2, 16-bit values.
the first value = high surrogate
the second value = low surrogate

Question 8

what are the advantages and disadvantages of UTF-8

Answer 8

advantages:
- existing ASCII files are in utf-8
- most broadly supported encoding form today

disadvantages:
- ideographic languages required 3 bytes/character so utf-8 encodings are larger than most existing encodings

Question 9

what are the advantages and disadvantages of UTF-16

Answer 9

advantages:
- allows all Unicode code points to be mapped into 2 bode units (bytes)

disadvantages:
- Latin text = x2 large therefore single-byte encodings
- not backward/forwards compatible with ASCII so programs that expect single-byte character sets won’t work in UTF-16

Question 10

what are the advantages and disadvantages of UTF-32

Answer 10

advantages:
- simple: allows all code points to be mapped into 1 fixed-length code units

disadvantages:
- Latin texts = x4 large therefore single-byte encodings
- not backward/forwards compatible with ASCII so programs that expect single-byte character sets won’t work in UTF-32

Question 11

encoding model

Answer 11

3 level model:

1. abstract character repertoire
2. code space
3. encoding forms

Question 12

code space

Answer 12

mapping to a set of integers, where a particular integer in set is known as the code points

Question 13

encoding forms

Answer 13

once defined mapping from abstract character set to set of integers further mappings is required.

character encoding form & character encoding scheme

Question 14

character encoding form

Answer 14

a mapping from a set of integers to a set of sequences of code units of specified width

Question 15

character encoding scheme

Answer 15

a mapping from a set of sequences of code units to a. serialised sequence of bytes

Question 16

challenges of character encoding

Answer 16

generality, character set specification, hardware issues, variable/fixed width, interoperability