Statements
A given statement may define one or more variables, use one or more variables, or both
When control arrives at a statement, certain previously executed definitions are available to be used in the statement
Likewise, after control leaves a statement certain definitions are available to subsequent statements
- Definitions made to variables in the statement
- Definitions made to variables in previous statements that were not overridden in the statement
To prevent ripple effects, we need to accurately determine the definitions that reach and leave each statement