<system diagram> ::=
[<package reference area>]
is associated with
{<frame symbol> contains
{<system heading>
{{<system text area>}*
{<macro diagram>}*
<block interaction area>
{<type in system area>}*} set }
| <graphical typebased system definition>}
A System-definition is the SDL representation of a specification or description of a system.
A system is separated from its environment by a system boundary and contains a set of blocks . Communication between the system and the environment or between blocks within the system can only take place using signals. Within a system, these signals are conveyed on channels . The channels connect blocks to one another or to the system boundary.
Before interpreting a System-definition, a consistent subset (see §3.2.1) is chosen. This subset is called an instance of the System-definition. A system instance is an instantiation of a system type defined by a System-definition. The interpretation of an instance of a System-definition is performed by an abstract SDL machine which thereby gives semantics to the SDL concepts. To interpret an instance of a System-definition is to:
b) interpret the blocks and their connected channels which are contained in the consistent partitioning subset selected.