Language & Regular Expressions

Question 1

What is a basic Regex scenario?

Answer 1

Question 2

What are the different applications of language and regular expression?

Answer 2

• Processing data - sequences or strings
• Pattern matching in databases
• Text searching
• Checking inputs for conformity for compilers and grammar parsing

Example Applications

• Search and replace in text including programs
• Searching in gene/protein sequence databases

Question 3

What is the basic set notation - Element of…

Answer 3

Question 4

What is the basic set notation - Not an element of….

Answer 4

Question 5

What is the basic set notation - (proper) subset of…

Answer 5

Question 6

What is the basic set notation - Not a (proper) subset of…

Answer 6

Question 7

What is the basic set notation - Subset and equal to

Answer 7

Question 8

What is the basic set notation - Proper subset of

Answer 8

Question 9

What is the basic set notation - Union / ‘OR’

Answer 9

Question 10

What is the basic set notation - Intersection / ‘AND’

Answer 10

Question 11

What is the basic set notation - Not A

Answer 11

Question 12

What is the basic set notation - Empty Set {}

Answer 12

Question 13

What is the basic set notation - Cardinality (Size) of set A

Answer 13

Question 14

What are the basic set rules?

Answer 14

Question 15

What is the theory of formal languages?

Answer 15

• Certain letters form certain sentences which form certain paragraphs which form coherent stories
• Spoken languages are difficult to analyse
• Most universal language structure
  
  • Rules for the lang are explicitly stated
  • In terms of what strings of symbols can occur

Question 16

What are formal languages?

Answer 16

• Alphabet - finite set of fundamental units (symbols, letters and tokens)
  
  • Uses ∑ as the name of alphabet ∑= {a,q,r}
• Language - set of strings of symbols from the alphabet
  
  • As well as specific to the language
• Words - finite strings that are permissible
  
  • In the language which can be generated from the alphabet + rules of lang
• Empty, null string - Epsilon ε or Lambda

Question 17

How do you descibe abstract languages?

Answer 17

Question 18

How does concatenation work

Answer 18

Question 19

How does the length of strings work?

Answer 19

• Length of a string is the number of characters in the string
• length(ε) = 0 in any language that includes ε

Question 20

How does reversing strings work?

Answer 20

• Function which reverses strings
• Reverse(a) = the same strings and letters in backwards order
  
  • Reverse of a
  • Which is valid even if reverse(a) is not a word in the langague

Question 21

How does generalising the * operator to a set of words work?

Answer 21

• If S = set of words
• S* = the set of finite strings formed by concatenating words
• From S including ε where repetition is allowed

Question 22

What are regular expressions?

Answer 22

Question 23

What are the basic regex concepts?

Answer 23

Question 24

What is regex quantification?

Answer 24

Question 25

What are some pattern matching applications?

Answer 25

Test if a string matches some pattern

• Process natural language
• Scan for virus signatures
• Search for information on google

Parse Text Files

• Compile a java program
• Crawl + index the web

Question 26

WHat are the basic regex operations?

Answer 26

Question 27

What are some generalised regex?

Answer 27