1. SwE 455 Program Slicing

2. Our Goals Debug your thousands lines of code easily by reducing the complexity of the program Write a robust program before testing your code Save your regression testing time by limiting the tests to only those that exercise the changed code

3. Approach “Break your code into smaller pieces”

4. Program Slicing What is it? - A well-known program analysis and transformation technique that uses program statement dependence information to identify parts of a program that influence or are influenced by an initial set of program points of interest which is called the slice criteria - Introduced by Mark Weiser in his Ph.D. thesis (1979)

5. slicing criterion is provided by the user Source program Resulting slice Slice Slicing Criterion Slicing Criterion indirectly relevant indirectly relevant Program Slicing (cont’d)

6. Variants of Program Slicing Many different variants of program slicing exist 1.Static Slicing 2.Backward Slicing 3.Forward Slicing 4.Dynamic Slicing 5.Conditional Slicing 6.Chopping Also Many Different tools, however – Most program slicing tools are written for C but there are also some for C++ and Java – Most of these have problems with dynamic binding, inheritance, polymorphism and performance

7. Backward Slice Example public class SimpleExample { static int add(int a, int b){ return(a+b); } public static void main(final String[] arg){ int i = 1; int sum = 0; while (i < 11) { sum = add(sum, i); i = add(i, 1); } System.out.println("sum = " + sum); System.out.println("i = " + i); } Slicing Criterion Slicing Criterion

8. Forward Slice Example public class SimpleExample { static int add(int a, int b){ return(a+b); } public static void main(final String[] arg){ int i = 1; int sum = 0; while (i < 11) { sum = add(sum, i); i = add(i, 1); } System.out.println("sum = " + sum); System.out.println("i = " + i); } Slicing Criterion Slicing Criterion

9. Why is It Useful? Program slicing is useful in many different states of the software development lifecycle – 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 quality assurance Safety critical code can be isolated and functions can be implemented redundant and in functional diversity manner – Software measurement, Maintenance,….