Availability Guide for Application Design

Designing Applications for Change
Availability Guide for Application Design—525637-004
10-20
Using Version-Labeled Interfaces for Intermodule
Communication
messages and no longer have to ignore any fields. However, the modules still
perform with version N functions.
4. Version N+2 of module B is installed. Module B now contains the upgraded
function and is able to make use of the new fields in version N+1 messages.
Module A knows of the existence of these new fields but not of their use. However,
module A is able to intelligently reject their use.
5. Version N+2 of module A is now installed. Modules A and B can now make full use
of all the new features and functions.
Overlapping Ranges of Labeled Message Versions
Modules in well-designed applications often support a wider range of messages. The
sender of a message might support a wider range of messages than the module that
Note. Up to this point, it is still possible to revert back to version N functions and
messages. Once you complete the next step, you are committed; you can no longer
return to version N functions and messages.
Figure 10-3. Labeled Message Versions
Version N
and Version
N+1
Messages
A[N] B[N+1]
2. Module B understands new
message content
Version N
Messages
A[N] B[N]
1.
Modules A and B understand
old messages content and
old functions
Version
N+1
Messages
A[N+1]
B[N+1]3.
Modules A and B both
understand new message
content
Version
N+1
Messages
A[N+1] B[N+2]4.
Module B understands new
functions
Version
N+1
Messages
A[N+2] B[N+2]
5.
Modules A and B both
understand new functions
VST903.vdd