Table Of ContentA KNOWLEDGE-BASED APPROACH
TO PROGRAM UNDERSTANDING
THE KLUWER INTERNATIONAL SERIES
IN ENGINEERING AND COMPUTER SCIENCE
A KNOWLEDGE-BASED APPROACH
TO PROGRAM UNDERSTANDING
by
Salwa K. Abd-EI-Hanz
Cairo University, Egypt
Victor R. Basili
University of Maryland, U.S.A.
WKAP ARCHIEF
KLUWER ACADEMIC PUBLISHERS
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Printed on acid-free paper.
CONTENTS
LIST OF FIGURES ........................................................................................... vii
LIST OF TABLES ............................................................................................. ix
PREFACE ......................................................................................................... xi
ACKNOWLEDGMENTS .................................................................................. xv
1 INTRODUCTION ........................................................................................ 1
1.1 RESEAR.CH GOALS ......................................................................... 1
1.2 RESEAR.CH APPROACH ................................................................. 2
1.3 OUTLINE ......................................................................................... 4-
2 BACKGROUND .......................................................................................... 5
2.1 LOOP ANALYSIS ............................................................................ 5
2.1.1 Axiomatic Approaches ........................................................... 6
2.1.2 Non-axiomatic Approaches ..................................................... 8
2.1.3 Hybrid Approaches ................................................................. 9
2.1.4 Decomposition Approaches .................................................... 9
2.2 PROGRAM ANALYSIS AND UNDERSTANDING ......................... 9
2.2.1 Algorithmic Approaches ......................................................... 10
2.2.2 Cognitive Studies .................................................................... 11
2.2.3 Knowledge-Based Approaches ................................................ 12
3 OVERVIEW AND BASIC DEFINITIONS ................................................... 19
3.1 DEFINITIONS .................................................................................. 20
3.2 A LOOP TAXONOMY ..................................................................... 21
4 ANALYSIS OF FLAT LOOPS ..................................................................... 23
4.1 NORMALIZATION OF THE LOOP REPRESENTATION ............... 24
4.1.1 Normalization of the Loop Condition ...................................... 24
4.1.2 Normalization of the Loop Body ............................................. 24
4.2 DECOMPOSITION OF THE LOOP BODy ...................................... 25
4.3 FORMATION OF THE LOOP EVENTS ........................................... 28
4.4 A KNOWLEDGE BASE OF PLANS ................................................. 29
4.5 ANALYSIS OF THE EVENTS ......................................................... 40
vi A KNOWLEDGE-BASED APPROACH TO PROGRAM UNDERSTANDING
5 ANALYSIS OF NESTED LOOPS ................................................................ 41
5.1 DEFINITIONS .................................................................................. 43
5.2 ANALYSIS OF INNER LOOPS ........................................................ 45
5.3 REPRESENTATION OF INNER LOOPS ANALYSIS
RESULTS ................................................................................................. 46
5.4 ANALYSIS OFOUTERLOOPS ....................................................... 50
5.5 ADAPTATION OF INNER LOOPS SPECIFICATIONS ................... 54
5.5.1 Context Adaptation ................................................................. 54
5.5.2 Initialization Adaptation ......................................................... 56
6 DISCUSSION OF THE ANALYSIS APPROACH ........................................ 61
7 CASE STUDy .............................................................................................. 67
7.1 OBJECTIVES ................................................................................... 67
7.2 METHOD .......................................................................................... 67
7.3 RESULTS AND ANALySIS ............................................................. 69
8 PROTOTYPE IMPLEMENTATION ............................................................ 77
8.1 DESIGN ............................................................................................ 77
8.2 OPERATION .................................................................................... 79
9 APPLICATIONS .......................................................................................... 83
9.1 ASSISTING MAINTENANCE AND REUSE ................................... 83
9.2 ASSISTING FORMAL DEVELOPMENT ......................................... 84
9.2.1 ASSISTING THE VDM OPERATION REFINEMENT
PROCESS ......................................................................................... 85
9.2.2 ASSISTING THE Z OPERATION REFINEMENT
PROCESS ......................................................................................... 86
9.2.3 DISCUSSION ......................................................................... 87
10 CONCLUSIONS .......................................................................................... 89
10.1 SUMMARY OF APPROACH. .......................................................... 89
10.2 OBSERVATIONS ............................................................................ 90
10.3 FUTURE WORK .............................................................................. 91
REFERENCES .................................................................................................. 93
A NOTATION ................................................................................................ 99
A.l POINTER NOTATION .................................................................... 100
B ACRONYMS ............................................................................................... 103
C DEFINITIONS ............................................................................................. 105
D ADDITIONAL PLANS AND ABSTRACTION CLASSES .......................... 109
INDEX .............................................................................................................. 115
LIST OF FIGURES
2.1 Classification of related research ............................................................... 6
3.1 Overview ofthe analysis approach ............................................................ 19
4.1 Analysis of flat loops ................................................................................. 23
4.2 Plan categories .......................................................................................... 31
4.3 Generic template of a Determinate Basic Plan ........................................... 31
4.4. Generic template of a Simple Augmentation Plan .................................... 31
4.5 Generic template of an Indeterminate Basic Plan ...................................... 32
4.6. Generic template of a General Augmentation Plan ................................... 32
4.7. A Determinate Basic Plan ........................................................................ 33
4.8. A Simple Augmentation Plan. .................................................................. 34
4.9 An Indeterminate Basic Plan. .................................................................... 35
4.10 A General Augmentation Plan .................................................................. 36
4.11 The tree structure of a plan ....................................................................... 37
4.12 Structural improvement to the plan SAP1 ................................................. 38
4.13 Structural improvement to the plan IBP2 .................................................. 39
4.14 Four variations ofloop control computation .............................................. 39
5.1 A nested structure of while loops ............................................................... 42
5.2 A plan for finding the minimum ............................................................... 45
5.3 An abstraction class for ascending enumeration ........................................ 48
5.4 An abstraction class for finding the minimum ........................................... 49
5.5 New plan categories .................................................................................. 50
5.6 First example of a Simple High-level Augmentation Plan ......................... 51
5.7 Second example of a Simple High-level Augmentation Plan ..................... 51
6.1 A Determinate Basic Plan for detecting faults ........................................... 63
7.1 Partially analyzed loop number pI ............................................................ 73
7.2 Partially analyzed loop number p9 ............................................................ 74
8.1 Structure of LANTeRN ............................................................................. 78
8.2 LANTeRN's output for the program in Example 8.1 ................................. 81
viii A KNOWLEDGE-BASED APPROACH TO PROGRAM UNDERSTANDING
9.1 VDM operation specification .................................................................... 86
D.l A plan for descending enumeration .......................................................... 109
D.2 An abstraction class for descending enumeration ..................................... 110
D.3 A plan for scanning a linked list .............................................................. 110
D.4 A plan for conditional ascending enumeration ......................................... 111
D.5 A plan for conditional scanning of a linked list ........................................ III
D.6 A plan for modifying arrays ..................................................................... 112
D.7 A plan for finding the location of the minimum ....................................... 112
D.8 An abstraction class for finding the location of the minimum ................... 113
D.9 A plan which does not contribute to loop specifications ............................ 1l3
D.I0 A plan for ignoring error messages .......................................................... 114
LIST OF TABLES
3.1 The three dimensions used for classifying loops .......................................... 22
7.1 Number of completely analyzed loops along the three dimensions ............... 69
7.2 Number of completely analyzed loops in the available classes ..................... 69
7.3 Utilization of the designed plans in the six possible categories .................... 71
7.4 Utilization of each of the designed plans ..................................................... 71
7.5 Number of events in the analyzed loops ...................................................... 74
7.6 Characteristics of the 12 partially analyzed loops ........................................ 75
7.7 Comparison between the completely and partially analyzed loops ............... 75
PREFACE
Program understanding plays an important role in nearly all software related
tasks. It is vital to the development, maintenance and reuse activities. Program
understanding is indispensable for improving the quality of software development.
Several development activities such as code reviews, debugging and some testing
approaches require programmers to read and understand programs. Maintenance
activities cannot be performed without a deep and correct understanding of the
component to be maintained. Program understanding is vital to the reuse of code
components because they cannot be utilized without a clear understanding of what
they do. If a candidate reusable component needs to be modified, an understanding
of how it is designed is also required.
This monograph presents a· knowledge-based approach to the automation of
program understanding. This approach generates rigorous program documentation
mechanically by combining and building on strengths of a practical program
decomposition method, the axiomatic correctness notation, and the knowledge
based analysis approaches. More specifically, this approach documents programs by
generating first order predicate logic annotations of their loops. In this approach,
loops are classified according to their complexity levels. Based on this taxonomy,
variations on the basic analysis approach that best fit each of the different classes
are described. In general, mechanical annotation of loops is performed by first
decomposing them using data flow analysis. This decomposition encapsulates
interdependent statements in events, which can be analyzed individually.
Specifications of the resulting loop events are then obtained by utilizing patterns,
called plans, stored in a knowledge base. Finally, a consistent and rigorous
functional abstraction of the whole loop is synthesized from the specifications of its
individual events.
The aforementioned plans are units of knowledge required to identify abstract
concepts in a program. The basic structure of a knowledge base plan has two parts:
the antecedent and the consequent. The; antecedent represents the knowledge which
is necessary for the recognition of stereotyped loop events. The consequent
