Echelon DM-21 Device Manager - Manual (Page 88)

7-2 Advanced Topics
Database Synchronization
Several Device Managers may be used together to manage a large system (see
Using Subsystems in Chapter 1). There were two ways in which this can be
accomplished:
1. All subsystems can be loaded into every Device Manager, and each Device
Manager can be instructed at runtime as to which subsystem to apply based
on its 4-bit subsystem selection input;
2. Each Device Manager is loaded with a single subsystem, and is responsible
for managing only that portion of the network associated with its subsystem.
When all subsystems fit into the Device Manager’s memory, the first option
provides much more flexibility by permitting Device Managers to be programmed
in the factory and shipped to the field since any Device Manager can manage any
part of the system based on the 4 bit subsystem selection input.
The first option raises the problem of database synchronization. Imagine an
installation where five Device Managers are needed to manage the network. The
five Device Managers are programmed and installed in year 1. In year 4 it is
necessary to replace a Device Manager. Over the three-year period enhancements
have been made to the original database. If the enhanced database was loaded
into a replacement Device Manager and then installed in the four year old
network, there is a possibility that the enhanced Device Manager would be
incompatible with the original database.
To easily detect such an incompatibility, assign a database version number when
the managed device list is loaded into the Device Manager. This is accomplished
on the window of the Device Manager Loading Wizard shown in figure 7.1 (see
step 11 of Example 1 in Chapter 5).