- each `DataDeclaration` must have a `position` and a `physical size` - the `physical size` of an elementary item is given by the PICTURE clause - the `position` is the sum of the `physical size`s of all data declared before - a group item also have a size and a position - the `physical size` of a group item is the sum of all its children - the `position` is the sum of the `physical size`s of all data declared before - an array `phsyical size` is equal to its `length` times its `physical size` - the `position` of the first data of a program is **1**
