Within the common elements, the data types are defined. Data typing prevents errors in an early stage. It is used to define the type of any parameter used. This avoids for instance dividing a Date by an Integer.
Common data types are Boolean, Integer, Real and Byte and Word, but also Date, Time_of_Day and String. Based on these, one can define own personal data types, known as derived data types. In this way one can define an analogue input channel as data type, and re-use this over and over again.