A way to improve the situation would be to supply the user
with a mechanism to reuse the abstract data tapes.
5.1 Object-oriented programming
Booch has concluded in his work (1985) about object-
oriented development that reusable software components tend
to be objects or. classes of objects. According to Booch, an
object is an entity that
- has state
- is characterized by the actions that it suffers and
that it requires of other objects
- is an instance of some (possibly anonymous) olass
—- is denoted by name
- has restricted visibility of and by other objects
- may be viewed either by its specification or by its
implementation
If we apply the object-oriented programming paradigm to the
matrix example, a matrix can be considered to be an object.
From the implementation point of view, the definition part
of an ADA package declares the visible part of an object or
an object class. Then, the actual implementation is hidden
in the body of the package.
What does a user benefit from the object-oriented approach?
One of the biggest advantages is that the definition part
defines the data types as well as the operations. Compared
to a FORTRAN approach, much less documentation is required.
In addition, the linking mechanism of an ADA environment
ensures that all the types and procedure calls are
consistent. Thus, the main burden of testing is transfered
from run time testing to compilation and linking phase.
6. SPECIAL KINDS OF OBJECTS
6.1 Data bases
Data bases have been used in photogrammetry for some time.
The purpose has been to store pertinent data for a longer
time, not only for the time a program is running. Magnetic
disks are used as storage media almost exclusively.
On an abtract level, data base is a collection of data plus
a well defined interface for dealing with the data:
retrieve, insert, delete and update it. When the usual
assumptions of long life time and storage on permanent mass
storage device are left out, data base concept can be used
as a squeleton for a programming paradigm. In the
following, the use of data base concept in photogrammetric
systems is studied, starting from the most global level.
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