When a PL/I program is executed, it can manipulate many different DATA items of particular data TYPES. Each data item, except an unnamed arithmetic or string constant, is referred to in the program by a NAME. Each data name is given attributes and a meaning by a declaration (explicit or implicit).

A data item is either the value of a variable or a constant. (Note that these terms, as used here, are not exactly the same as in general mathematical USAGE.) Data items can be single items, called scalars, or they can be a collection of items called data aggregates that are groups of data items that can be referred to either collectively or individually. The types of data aggregates are arrays, structures, and unions.

A variable has a value or values that might CHANGE during execution of a program. A variable is introduced by a declaration, which declares the name and certain attributes of the variable. A name is explicitly declared if it appears in a DECLARE statement that explicitly declares attributes of names.

A constant has a value that cannot change. Constants for computational data are referred to by stating the value of the constant or naming the constant in a DECLARE statement.

When a PL/I program is executed, it can manipulate many different data items of particular data types. Each data item, except an unnamed arithmetic or string constant, is referred to in the program by a name. Each data name is given attributes and a meaning by a declaration (explicit or implicit).

A data item is either the value of a variable or a constant. (Note that these terms, as used here, are not exactly the same as in general mathematical usage.) Data items can be single items, called scalars, or they can be a collection of items called data aggregates that are groups of data items that can be referred to either collectively or individually. The types of data aggregates are arrays, structures, and unions.

A variable has a value or values that might change during execution of a program. A variable is introduced by a declaration, which declares the name and certain attributes of the variable. A name is explicitly declared if it appears in a DECLARE statement that explicitly declares attributes of names.

A constant has a value that cannot change. Constants for computational data are referred to by stating the value of the constant or naming the constant in a DECLARE statement.