[SDL Forum Society - Logo] Tutorial on SDL-88
Belina, Hogrefe (edits Reed)

5.1 Block substructure

Home Up Next

This feature is not supported in SDL-2000.

In 'Basic system structure' it was stated that a block contains processes, interconnected by signal routes. Sometimes further structuring of a block is necessary, so that a block may have a substructure. An example is given in figure 28. The block B contains the process types P1 and P2. In addition, it contains a substructure, referenced by the little rectangle containing the name B of the block substructure.

wpe5.gif (4147 bytes)

Figure 28: Block diagram with substructure reference

The substructure is described by a substructure diagram in figure 29. The substructure diagram is similar to a system diagram (except for the channels connected to the block). In figure 29 it contains the blocks B1, B2 and B3.

wpeC.gif (5967 bytes)

Figure 29: Block substructure diagram

The interface of the substructure to its environment must be the same as that of the block.

wpe4.gif (3988 bytes)

Figure 30: Shorthand for block partitioning

A block definition containing process definitions corresponds to a leaf-block in the system. A block definition containing a substructure definition corresponds to a partitioned block in the system. A choice between these two versions of a block must be made before interpretation time. The result is called consistent partitioning subset. There are some rules for the selection of a consistent partitioning subset, ensuring that it corresponds to a valid block tree (e.g. each branch must terminate in a leaf-block, each block must be connected, directly or indirectly, to the root).

If a block contains only a substructure and no processes, there is a shorthand as shown in figure 30. In this example, block B1 does not contain any processes, but is partitioned into the blocks B11, B12 and B13.

Home Up Next

Contact the webmaster with questions or comments about this web site.
Copyright 1997-May, 2013 SDL Forum Society