Data Flow Analysis, Control Flow Graphs

Question 1

What are modern compilers

Answer 1

Static analysis tools to detect defects such as syntax errors
Correct data type usage
Undeclared variables
Unreachable code
This is assisted by data flow analysis and control flow analysis

Question 2

Data flow analysis

Answer 2

Concerned with how data is used on different paths through the code
There are 3 different usage states for each data variable
Undefined - data has no defined value
Defined
Referenced - the data is used
It can’t detect errors

Question 3

Data flow can detects anomalies

Answer 3

Ur-anomaly an undefined data item is read on a program path
Du-anomaly data item that has been assigned a value, becomes undefined without being used
Dd-anomaly a data item that has been assigned a value is assigned another value without being used in the meantime

Question 4

Program flow graphs

Answer 4

Describes program control flow, each branch shown as separate path and loops are shown by arrows looping back to loop condition node
Control flow graph is a graphical representation of a programs control structure

Question 5

Path testing

Answer 5

Desired paths through program executed at least once
Starting point for path testing is a program flow graph that shows nodes representing program decisions and arcs representing control flow
Statements with conditions are therefore nodes in the flow graph

Question 6

What is a decision

Answer 6

Program point at which the control can diverge (e.g. if and case statements)

Question 7

What is a junction

Answer 7

Program point where the Control flow can merge e.g. end if, end loop

Question 8

What is a process block

Answer 8

Sequence of program statements uninterrupted by either decisions or junctions e.g, straight line code. A process has one entry and one exit. A program does no jump into or out of process

Question 9

Paths consist of

Answer 9

Segments, the smallest segment is a link. A link is a single process that lies between 2 nodes.
The length of a path is number of links in a path. An entry/exit path or a complete path is a path that starts at a routines entry and ends at the same routines exit

Question 10

Why are complete paths useful for testing

Answer 10

Difficult to set up and executed paths that start at an arbitrary statement
Difficult to stop at an arbitrary statement