PPT ON PROGRAM SLICING BY KUMARI NUTAN

1. KUMARI NUTAN
O901206358
UNDER THE GUIDANCE OF
ER. RAJESH KU. SAHOO
Seminar on:
pROGRAM SLICING TECHNIQUE
Represented by
AJAY BINAY INSTITUTE OF TECHNOLOGY, CUTTACK
BPUT, ODISHA

2. ABSTRACT
 Slicing is a program analysis technique for
debugging and understanding programs.
 Program slicing is potentially useful analysis for
aiding program understanding.
 A program slice consists of the parts of a program
that potentially affect the values computed at some
point of interest. The task of computing program
slices is called program slicing.

3. CONTENTS
 Introduction
 Program Slicing basic idea..
 Slices & Slicing criteria
 Why program slicing useful?
 How?
 Intermediate Representation of programs for slicing
 Slicing classification
 Slicing properties
 Applications of slicing
 Characteristics
 Conclusion
 References

4. INTRODUCTION
 Program slice is a subset of program .
 Program slicing enables programmers to view
subsets of program.
 Proposed as an approach to aid program
understanding task.
 Original concept was introduced by “Mark Weiser”
in his Ph. D thesis (1979).

5. PROGRAM SLICING BASIC IDEA…..
 Method used for abstracting from programs.
• Start with a subset of a program’s behaviour and
reduce it to a minimal from that still produces that
behavoiur.
 The reduced program is called a “SLICE”.
 Finding a slice is in general unsolvable .

6. SLICES & SLICING CRITERIA
 Slicing criterion – a pair <i, v>
 “i” is the number of the statement & “v” is the set
of variables to be observed at statement “i”.
 Desirable properties of a slice:
 Must have been got from the actual program by
deletion.
 Must be syntactically correct .
 Behavior of slice must corresponds to original
program behavior.

7. WHY PROGRAM SLICING USEFUL?
 Debugging:
Slicing visualizes control and data
dependencies
It highlights statements influencing the slice
 Testing:
Tests may be decomposed and test- work
gets faster and more efficient.
 Software measurement & maintEnance , …..

8. I’ll slice
you into
smaller
pieces
Using This?
Don’t even think about this way!!!

9. HOW?
 A slice is constructed by deleting those parts of a
program which is irrelevant to the program with
respect to the chosen set of variables at the chosen
point.
 A slice is taken from a program with the slicing
criterion <s , v>, which specifies a location
(Statement s) and a variable (v).

10.  slicing criterion is provided by the user
Source program Resulting
slice
Slice
Slicing
Criterion
indirectly
relevant
FLOW DIAGRAM

11.  Intermediate Representation of programs for slicing:
 Control Flow Graph (CFG)
Data Flow equations are solved
 Program Dependence Graph (PDG)
Slice is computed as graph reachability
problem

12. Entry
x=1 i=0 while i<2
i++ if i<2
x=2 x=3
z=x
Control dependence edges
Data dependence edges
PROGRAM DEPENDENCE GRAPH
1. x=1;
2. i=0;
3. while (i<2) {
4. i++;
5. if (i<2)
6. x=2;
else
7. x=3;
8. z=x;
}

13. SLICING CLASSIFICATIONS
 Types of slices
 Static
 Dynamic
 Direction of slicing
 Backward
 Forward
 Executability of slice
 Executable
 Closure
 Levels of slices
 Intraprocedural
 Intrprocedural

14. SLICING PROPERTIES
Static Slicing
 Slices derived from the source code for all possible
input values
 No assumptions made on input
 May leads to relatively big slice
 Contains all statements that may affect a variable
for every possible execution
 Result may not be usefull

15. SLICING PROPERTIES
Dynamic Slicing
 Computed on a given input
 Deterministic instead of Probabilistic
 Useful for applications that are input driven
(debugging, testing)

16. BACKWARD STATIC SLICING
 A backward slice of a program with respect to a
program point p and set of program variables V
consists of all statements and predicates in the
program that may affect the value of variables in V
at p

17. FORWARD STATIC SLICING
 A forward slice of a program with respect to a
program point p and set of program variables V
consists of all statements and predicates in the
program that may be affected by the value of
variables in V at p

18. APPLICATIONS OF SLICING
 Differencing
 Debugging
 Testing
 Program understanding
 Software maintenance
 Complexity measurement
 Program integration
 Reverse engineering
 Software Quality Assurance

19. CHARACTERISTICS
 Advantages
 Very easy and fast to compute a dynamic slice at
any execution point.
 Disadvantages
 Dynamic dependence graph is very large for real
programs…so, this scheme is not practical.

20. CONCLUSION
 No Universal algorithm
 Improving performance
 New algorithms

21. REFERENCES
 www.google.com.
 www.altavista.com
 www.wikipedia.com.

22. ????