Environmental Engineering Reference
In-Depth Information
appropriate as a developmental basis for (ordinary) differential equation systems. It is
less suitable to describe structurally heterogeneous settings, where it is not reasonable
to define internally homogeneous variables, where the internal heterogeneity is of
crucial interest. Also, the approach is not well suited if it is required to describe
systems that vary in time not only quantitatively but also change their structure in a
pronounced way. For this kind of application case, “structural dynamic modelling”
was developed as an extension (see Chap. 19). Starting the operations in terms of
establishing and interrupting relations, adding and removing components is the field of
object-oriented systems analysis, which was derived from the according computer
programming paradigm (object oriented programming).
4.4 Non-Classical System Approaches: Object-Oriented
Systems Analysis
The object-oriented systems analysis (OOSA) originated in computer science in the
context of object-oriented programming. It is the conceptual background of program-
ming languages, which allow some self-organization and self-modification features
of the executable programme. In fact, OOSA is more general than the “general
systems” approach, which can be thought as a sub-set of what object orientation
can deal with. In the following, we give a brief introduction into the object-oriented
programming paradigm (OOP) and use it for systems analytical purposes. More
elaborated descriptions can be found at Rumbaugh et al. (1991) and Hill (1996)
and in the chapter on individual-based models (Chap. 12). The term “object-oriented
systems analysis” refers to specific features of modern computer programmes.
In computer science, a
class
is a unit that can be specified in a computer
programme. It consists of storage reservations for variables as well as executable
statements of computer code. The specific feature of a class allows it to be copied
(“instantiated”) various times during programme execution. Then, the copies are
referred to as
objects
. In order to distinguish several copies of a class during
programme execution a special type of variable (“reference variable” or “pointer”)
is required. A pointer contains the address where the object can be found in the
computer storage. Hence, using pointers, it is possible to specify relations and also
interactions between objects.
4.4.1 Object Oriented Systems Analysis Facilitates Structurally
Dynamic System Representations
For ecological applications, classes can be used to describe the set of states and
activities of organisms and individuals. Using OOP it is conveniently possible to use
one generic description to simulate large numbers of individuals performing their
activities independently of each other. OOP allows to handle
structurally variable
interaction networks
. This largely extends the range of phenomena that can be
