Design Concepts
The design concepts provide the software designer with
a foundation from which more sophisticated methods can be applied. A set of
fundamental design concepts has evolved. They are:
1. Abstraction
- Abstraction is the process or result of generalization by reducing the
information content of a concept or an observable phenomenon, typically in
order to retain only information which is relevant for a particular purpose.
2. Refinement
- It is the process of elaboration. A hierarchy is developed by decomposing a
macroscopic statement of function in a step-wise fashion until programming
language statements are reached. In each step, one or several instructions of a
given program are decomposed into more detailed instructions. Abstraction and
Refinement are complementary concepts.
3. Modularity -
Software architecture is divided into components called modules.
4. Software Architecture - It refers to the
overall structure of the software and the ways in which that structure provides
conceptual integrity for a system. A good software architecture will yield a
good return on investment with respect to the desired outcome of the project,
e.g. in terms of performance, quality, schedule and cost.
5. Control Hierarchy - A program structure that
represents the organization of a program component and implies a hierarchy of
control.
6. Structural Partitioning - The program
structure can be divided both horizontally and vertically. Horizontal
partitions define separate branches of modular hierarchy for each major program
function. Vertical partitioning suggests that control and work should be
distributed top down in the program structure.
7. Data Structure - It is a representation of the
logical relationship among individual elements of data.
8. Software Procedure - It focuses on the
processing of each modules individually
9. Information Hiding - Modules should be
specified and designed so that information contained within a module is
inaccessible to other modules that have no need for such information
Design
considerations
There are
many aspects to consider in the design of a piece of software. The importance
of each should reflect the goals the software is trying to achieve. Some of
these aspects are:
• Compatibility - The software is able to
operate with other products that are designed for interoperability with another
product. For example, a piece of software may be backward-compatible with an
older version of itself.
• Extensibility - New capabilities can be added
to the software without major changes to the underlying architecture.
• Fault-tolerance - The software is resistant
to and able to recover from component failure.
• Maintainability - A measure of how easily bug
fixes or functional modifications can be accomplished. High maintainability can
be the product of modularity and extensibility.
• Modularity - the resulting software comprises
well defined, independent components. That leads to better maintainability. The
components could be then implemented and tested in isolation before being
integrated to form a desired software system. This allows division of work in a
software development project.
• Reliability - The software is able to perform
a required function under stated conditions for a specified period of time.
• Reusability - the software is able to add
further features and modification with slight or no modification.
• Robustness - The software is able to operate
under stress or tolerate unpredictable or invalid input. For example, it can be
designed with resilience to low memory conditions.
• Security - The software is able to withstand
hostile acts and influences.
• Usability - The software user interface must
be usable for its target user/audience. Default values for the parameters must
be chosen so that they are a good choice for the majority of the users
• Performance - The software performs its tasks
within a user-acceptable time. The software does not consume too much memory.
• Portability - The usability of the same
software in different environments.
• Scalability - The software adapts well to
increasing data or number of users
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