Difference between revisions of "Theoretical Aspects of Lexical Analysis/Exercise 2"

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< Theoretical Aspects of Lexical Analysis
(DFA)
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   node [shape=none,fixedsize=true,width=0.2,fontsize=10]
 
   node [shape=none,fixedsize=true,width=0.2,fontsize=10]
 
   " {0, 1, 2}" -> "{}" [label="NF",fontsize=10]
 
   " {0, 1, 2}" -> "{}" [label="NF",fontsize=10]
   " {0, 1, 2}" -> "{0, 1, 2}" [label="F",fontsize=10]
+
   " {0, 1, 2}" -> "{0, 1, 2}" [label=" F",fontsize=10]
   "{0, 1, 2}" -> "{0, 1, 2} " [label="a,b",fontsize=10]
+
   "{0, 1, 2}" -> "{0, 1, 2} " [label=" a,b",fontsize=10]
 
   fontsize=10
 
   fontsize=10
 
   //label="Minimization tree"
 
   //label="Minimization tree"

Revision as of 02:31, 22 March 2009

Use Thompson's algorithm to build the NFA for the following regular expression. Build the corresponding DFA and minimize it.

  • (a*|b*)*

Solution

NFA

The following is the result of applying Thompson's algorithm.


DFA

Determination table for the above NFA:

In α∈Σ move(In, α) ε-closure(move(In, α)) In+1 = ε-closure(move(In, α))
- - 0 0, 1, 2, 3, 5, 6, 7, 9, 10, 11 0
0 a 4 1, 2, 3, 4, 5, 6, 7, 9, 10, 11 1
0 b 8 1, 2, 3, 5, 6, 7, 8, 9, 10, 11 2
1 a 4 1, 2, 3, 4, 5, 6, 7, 9, 10, 11 1
1 b 8 1, 2, 3, 5, 6, 7, 8, 9, 10, 11 2
2 a 4 1, 2, 3, 4, 5, 6, 7, 9, 10, 11 1
2 b 8 1, 2, 3, 5, 6, 7, 8, 9, 10, 11 2


Graphically, the DFA is represented as follows:


Given the minimization tree to the right, the final minimal DFA is:


The minimization tree is as follows. As can be seen, the states are indistinguishable.