Information Technology Reference
In-Depth Information
are known by the system." An example of such an invariant schema is shown
in figure 3.1.
A static schema models assertions that must be true at a single moment
in time. A common use of a static schema is to specify a given state of a set
of information objects, in situations of particular interest to the modeller. For
instance, it might describe the final state of a successful repair order.
3.3 Writing Information Specifications
This section describes how to use the concepts and structuring rules of the
information language to write an ODP information specification. We need
to describe the process of developing the specification, and the notation to
use. RM-ODP does not impose any methodology to build the information
specifications, but, to illustrate the ideas, we will follow a simple process by
which we specify:
1. The types of the information objects and the types of the relationships
between information objects.
2. The types of the information actions that can happen during the oper-
ation of the system.
3. A set of dynamic schemata that describe the behaviour of the objects
when the actions occur.
4. A set of invariant schemata that describe the constraints on the system
elements.
5. A set of static schemata which provide instantaneous views of the system
or of any of its constituent objects.
There are many possible options for representing the information language
concepts, depending on the experience and skills of the information modeller;
Entity-Relationship Models (ERM), Object Role Models (ORM) or UML class
diagrams can all be used. In this topic, we will make use of the corresponding
UML4ODP profile, which provides a set of UML elements to write information
specifications in UML.
3.3.1 Information Object Types
In the first place, we need to specify the types of the information objects
that model the data being handled by our ODP system. Information objects
are generally specified in terms of their types, which in UML are expressed by
classes stereotyped as
«
IV Object
»
.
