There are two different kinds of data types:

- An atomic type is atomic in the sense that it is not defined based on any other type and cannot be divided into parts or components, e.g. num.

- A record data type is a composite type with named, ordered components, e.g. pos. A component may be of an atomic or record type.A record value can be expressed using an aggregate representation;e.g. [ 300, 500, depth ] pos record aggregate value.A specific component of a record data can be accessed by using the name of that component; e.g. pos1.x := 300; assignment of the x-component of pos1.

Each available data type is either a value data type or a non-value data type. Simply speaking, a value data type represents some form of "value". Non-value data cannot be used in value-oriented operations:

•  Initialisation

•  Assignment (:=)

•  Equal to (=) and not equal to (<>) checks

•  TEST instructions

•  IN (access mode) parameters in routine calls

•  Function (return) data types

The input data types (signalai, signaldi, signalgi) are of the data type semi value. These data can be used in value-oriented operations, except initialisation and assignment. In the description of a data type it is only specified when it is a semi value or a nonvalue data type.

An alias data type is defined as being equal to another type. Data with the same data types can be substituted for one another. Example: VAR dionum high:=1;VAR num level; This is OK since dionum is an alias level:= high; data type for num

<type definition>::=

[LOCAL] ( <record definition>

| <alias definition> )

| <comment>

<record definition>::=

RECORD <identifier>

<record component list> ’;’

<record component list> ::=

<record component definition> |

<record component definition> <record component list>

<record component definition> ::=

<data type> <record component name>

<alias definition> ::=

ALIAS <data type> <identifier> ’;’

<data type> ::= <identifier>