Variables are placeholders for data which has been stored, or is to be stored, and as such are important components of procedures. They can take on various values.
Variables in SDF-P, which are also called S variables, are uniquely identified by their variable name and their scope.The scope determines where a variable can be accessed, whether in the current procedure only or throughout the entire task. Another important attribute of variables is the data type, which determines the values that a variable can assume.
A distinction is made between simple and complex variables: simple variables cannot be “divided” further, while complex variables consist of variable elements (variable elements can themselves be simple or complex variables). There are three types of complex variables: lists, arrays and structures.
Important features that contribute to programming convenience are:
implicit variable declaration
dynamically changing data type
dynamic expansion of complex variables
On the other hand, runtime security is ensured through:
explicit variable declaration
fixed data type
static structures
The variable concept of SDF-P takes all these features into account. A brief description of each is given in the sections below.