المحاضرة الخامسة-احتسابية1

• Regular Expressions
is a set of symbols, Thus if alphabet= {a, b}, then aab, a, baba, bbbbb, and baaaaa would all be strings of symbols of alphabet.
Regular expressions can be used to define languages. A regular expression is like a "pattern"; strings that match the pattern are in the language, strings that do not match the pattern are not in the language. The construction of regular expressions is defined recursively, starting with primitive regular expressions, which can be composed using typical operators to form more complex regular expressions.
In addition we include an empty string denoted by _ which has no symbols in it.
Definition of Regular Expressions :
Let ? be a given alphabet.
• ?, ?, a, for a ? ? are (primitive) regular expressions.
If r, r1, r2 are regular expressions, then
• r* star closure
• r1 • r2 concatenation
• r1 + r2 union
• Regular Expressions
is a set of symbols, Thus if alphabet= {a, b}, then aab, a, baba, bbbbb, and baaaaa would all be strings of symbols of alphabet.
Regular expressions can be used to define languages. A regular expression is like a "pattern"; strings that match the pattern are in the language, strings that do not match the pattern are not in the language. The construction of regular expressions is defined recursively, starting with primitive regular expressions, which can be composed using typical operators to form more complex regular expressions.
In addition we include an empty string denoted by _ which has no symbols in it.
Definition of Regular Expressions :
Let ? be a given alphabet.
• ?, ?, a, for a ? ? are (primitive) regular expressions.
If r, r1, r2 are regular expressions, then
• r* star closure
• r1 • r2 concatenation
• r1 + r2 union