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Character Sequence "ZCZC" Can Be in The Following States. Detected

This document discusses state graphs and transition testing. It provides examples of state graphs for an automobile transmission and a character detection program. It then walks through converting a set of specifications into a state graph and state table for an error detection program. The specifications describe maintaining an error counter, actions for different numbers of errors like rewriting or erasing, and transitioning between states. Developing the state graph and table helps uncover a contradiction in one of the specifications.

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abhi
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116 views4 pages

Character Sequence "ZCZC" Can Be in The Following States. Detected

This document discusses state graphs and transition testing. It provides examples of state graphs for an automobile transmission and a character detection program. It then walks through converting a set of specifications into a state graph and state table for an error detection program. The specifications describe maintaining an error counter, actions for different numbers of errors like rewriting or erasing, and transitioning between states. Developing the state graph and table helps uncover a contradiction in one of the specifications.

Uploaded by

abhi
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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10/26/2012

State Graphs
A state is defined as : A combination of
circumstances or attributes belonging for the time
being to a person or thing.
For example, a moving automobile whose engine is
running can have the following states with respect to
its transmission.

UNIT 7
STATES,STATE GRAPHS AND
TRANSITION TESTING
D.ABHISHEKH MS(SE)

Reverse gear
Neutral gear
First gear
Second gear
Third gear
Fourth gear

State graph - Example

For example, a program that detects the


character sequence ZCZC can be in the
following states.
Neither ZCZC nor any part of it has been
detected.
Z has been detected.
ZC has been detected.
ZCZ has been detected.
ZCZC has been detected.

A
A,C

A,C

Z,C,A

A
None

Z
Z

ZC

ZCZ
Z

ZCZC
C

Z
Z

10/26/2012

ERROR
STATE

OKAY

1/NONE

2/REWRITE

1/NONE

4/REWRITE

1/NONE

2/REWRITE

3/NONE

5/ERASE

1/NONE

6/ERASE

1/NONE

7/OUT

Example to convert specification into a state graph


---------------------------------------------------------------

TRANSITION BUGS

With an example, we will now follow a set of rules, i.e. specifications to


deduce the state graph and state tables
RULE 1:
The program will maintain an error counter which will be incremented
whenever there is an error.

10/26/2012

State table from the state graph(refer earlier slide for the
graph)

Initial state graph deduced from Rule1

INPUT

error

error

error

error

STATE

OKAY

ERROR

0/None

1/

...

Okay

RULE 1: The program will maintain an error counter,


which will be incremented whenever there is an
error.

Rule 2: If there is an error, rewrite the block


OKAY

ERROR

0/None

1/REWRITE

2/REWRITE

For all Error


2 entries, we include a Rewrite 3/REWRITE

4/REWRITE

5/REWRITE

6/REWRITE

7/REWRITE

8/REWRITE

2/

3/

4/

5/

6/

7/

8/

Rule 3: If there have been 3 successive errors, erase of tape and then rewrite the block

INPUT

STATE

STATE

OKAY

0/None

ERROR
INPUT
1/REWRITE

2/REWRITE
2
3

3/REWRITE,ERASE,REWRITE

The first 3rd successive error


occurs

4/REWRITE,ERASE,REWRITE

5/REWRITE,ERASE,REWRITE

6/REWRITE,ERASE,REWRITE

7/REWRITE,ERASE,REWRITE

8/REWRITE,ERASE,REWRITE

10/26/2012

Rule 4: If there have been 3 successive erasures,


and another error occurs, put the unit out of service
STATE

OKAY

ERROR

0/None

1/REWRITE

2/REWRITE

3/REWRITE,ERASE,REWRI
TE

4/REWRITE,ERASE,REWRI
TE
We have 3 successive erasures- so

Rule 5: If the erasure was successful, return to the


normal state and clear the error counter
STATE

OKAY

ERROR

0/None

1/REWRITE

1 3 after the 1st


We reach State
erasure. If successful, we return to
2
None & the error counter is made
0
3

service
4we now put the unit out of5/REWRITE,ERASE,REWRI
TE

6/OUT

0/None 4/REWRITE,ERASE,REWRI
TE

0/None

5/REWRITE,ERASE,REWRI
TE

0/None

6/OUT

Rule 6: If the rewrite was successful, decrement the


error counter and return to the previous state

2/REWRITE
3/REWRITE,ERASE,REWRI
TE

Conclusion

INPUT

STATE

OKAY

ERROR

0/None

1/REWRITE

0/None

2/REWRITE

1/None

3/REWRITE,ERASE,REWRI
TE

0/None
2/None

4/REWRITE,ERASE,REWRI
TE

0/None
5/REWRITE,ERASE,REWRI
3/None Example: Say we are
TEat state 1. The error

If we have a
0/None counter here is 2.6/OUT
successful(okay) rewrite, the entry for okay
4/None at state 2 will have error counter
decremented by 1 which is:
(2-1)/None where, None output for
success.

6
7

Observe the previous slideRULE6 states If the rewrite was successful, then
decrement the error counter and return to the
previous state.
The requirement probably was If there have been
no erasures and rewrite was successful, then
This has now resulted in contradictions which is a
concern as it might lead to bugs.
It is always unlikely that a contradictory specification
can result in a satisfactory implementation.

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