Concerning the relationships between object classes, the first version
of the model contains the same deficiencies as the SNMP MIB: There
arent't any inheritance and almost no containment relationships. In
contrast to this, the goal of object-oriented design is to model the
components and their relationships as realistic as possible. The
inheritance hierarchy indicates that one component is a refinement of
another one, e.g. a storage device is a special kind of device.
The System class becomes the root of the containment hierarchy
because the end user system is composed of other devices. The
definition of aggregation relationships is also straightforward: A System
contains at least one Processor (represented by a 1:n
relationship with n
1) but any number of
permanentStorageDevices (in this case, a 1:n relationship with
n0). A Printer, in contrast, is not part of a System
but a peripheral device; its connection to the system is expressed
by a simple 1:n relationship with n0. Figure
4 gives a overview of the relationships between some
object classes.
A special case of relationship can be found between the classes
Filesystem, Quota and Account. As the quota is a
property of a relationship between a user account and a filesystem,
the Quota object class becomes an association class of the
Filesystem--Quota relationship (see figure
5).