Page 45 - DCAP507_SYSTEM_SOFTWARE

Unit 2: Evolution of Operating System

control is applications configured as a compilation of weakly compatible expert diagrams Notes
(intended from mismatched control points of view?).
 Most standard diagrams were invented to reflect the associations and specifications to
execute controls in a specific hardware, instead of stating the proposed control aims in the
best hardware independent way.
 Frequently that hardware is so far out of date that many control engineers have only seen
its dependent simulation.
We require control demonstrations that reflect the contemporary computerized control system.
 As a consequence, it is fair to inquire if these diagrams are actually the best ease of use
demonstration for the application or the modern computer environment.
On the contrary, both the text and graphics elements in the Control Language have been
specifically intended to most evidently symbolize the intended application behavior. Particularly
the graphics have the following roles:
 Text Key Words are substituted by icons (e.g., Activity Brackets), intended to reflect the
underlying application structure visually.

 Icon diagrams are produced automatically (e.g., Idiom diagrams and Sequential Function
Charts) to exemplify programmed text.
 Just by their inclusion, diagrams and icons can offer visual structure and landmarks to a
program, cueing later searches.
 They are intended to strengthen the learning of a user.

2.4.2 Potential for Objects in Control

Objects symbolize a preferential sight of programming in which (ideally) all application data is
cataloged into data structures (the Objects), each type (Class) being defined with its access and
processing functions (the Methods). The concept permits programs (enclosing the programs
which define the Methods) to attach to the data in any Object via Messages (the calls to the
Method functions) to it.
The Object Class concept permits the definitions of alike application structures (the Classes) to
be dependent on each other via a concept of Inheritance and Overriding. The strength of this
capability is that it permits similar Objects to be considered similarly through Messages by
means of the same Method names, while the system makes the low level distinctions, choosing
the right Method variant for each Object. Every such Class may then be the foundation of any
number of functioning Instances, each accessed via the connected techniques.

Self Assessment

Fill in the blanks:
11. Practically, ............................. languages are superposed on collections of ancient control
data bases and illustrative demonstrations.
12. The ............................. Class concept permits the definitions of alike application structures
(the Classes) to be dependent on each other via a concept of Inheritance and Overriding.

2.5 OS User Viewpoint – Facilities

Every general-purpose computer must have an operating system to run other programs.
Operating systems perform basic tasks, such as recognizing input from the keyboard, sending

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