Information Technology Reference
In-Depth Information
However, if the viewpoints are to be developed by loosely coordinated teams,
it is not safe to assume they share a single namespace; it is just too expensive
to ensure that name assignments are unique. It is also often the case that the
correspondences are not simply one-to-one; the relationships will generally be
more complex.
This can be seen by considering the correspondences between the compu-
tational and engineering viewpoints (a situation similar to that between the
user and provider of middleware). The computational viewpoint takes a very
simple view of interactions, abstracting away from the platform-specific de-
tails of particular interactions; the engineering viewpoint, on the other hand,
abstracts away from most of the detail of the computational design, distin-
guishing just a few categories of interacting objects, not worrying about why
the interactions take place. Thus, the correspondences between computational
object types and basic engineering object types representing them are typically
not one-to-one. The correspondences often involve some level of abstraction
or filtering in one direction or the other.
1.3
Fundamental Concepts
Part 2 of the ODP Reference Model sets out a family of basic concepts,
explaining precisely what is meant when we say that ODP is based on an object
model. This is particularly important when dealing with the coordination of
a number of tools that all share the general idea of an object and an interface
at a ball and stick level, but often diverge in subtle ways when the fine detail
is examined.
Precision is essential when we are trying to bring together multiple view-
point languages, together with the languages implicit in the available tools, to
create a consistent framework. This integration depends on knowing exactly
what the basic concepts used are, and where they vary between languages.
The fundamental concepts are defined in a general way, and they can then
be used in any of the ODP viewpoints. Often, a concept is further specialized
in a particular viewpoint, but always in a way that is entirely consistent with
the basic definition. For example, the concept of an interface is defined in full
generality as one of the fundamental concepts, but viewpoints specialize it, so
that we have engineering interfaces, computational interfaces and so on.
This topic does not go into all the detail; that can be found in the stan-
dards. However, there are some fundamental concepts that are used in all the
viewpoint languages; these deserve to be discussed here. They are presented
in outline in this section, and more detail can often be found when they are
used later in the topic.
