Page 147 - DCAP308_OBJECT_ORIENTED_ANALYSIS_AND_DESIGN

Unit 12: System Design

and style. In this unit, we will discuss the concept of system design. Also, we will discuss various Notes
design decisions that are to be made during system design such as reuse plan, identifying
concurrency, allocation, software control strategy, etc.

12.1 System Design Overview

There are different approaches of System design Overview concerning various opinion. Let us
see some of them.

1. During system design the high-level of system architecture is chosen, the system is divided
into sub systems and concurrency is identified. Two objects are inherently concurrent if
they receive events at the same time and do not interact. If the events not are synchronized
the two objects cannot be on a single thread of control.

A thread of control is path through a set of state diagrams. Only a single object at a time
may be active on a thread. Sub systems are allocated to processors and tasks. Estimate
hardware resource requirements to decide if some subsystem shod be implemented in
hardware rather than in software. Allocate tasks to processor and determine physical
connectivity. Choose a strategy for management of data stores. Data stores are used to
give data some degree of permanency and to clearly separate subsystems. Data stores may
be implemented by using files or by databases. Identify and handle access to global
resources. Choose an approach to implement software control. Consider boundary
conditions including the issues of initialization, termination, and failure. See if a common
architectural framework might fit the application. Some common architectural frame
works are:

(a) Batch transformation – a data transformation is executed once on an entire input set.
(b) Continuous transformations – a data transformation performed continuously as
inputs change.

(c) Interactive interfaces – a system dominated by external interactions.
(d) Dynamic simulations – a system that simulates evolving real-world objects.
(e) Transaction managers – a system concerned with storing and updating data, often
including concurrent access from different physical locations.
2. During system analysis, the focus is on what needs to be done, independent of how it is
done. During design, developers make decisions about how the problem will be solved,
first a high level and then with more detail.
The system architecture determines the organization of the system into subsystems.

Notes A rough performance estimate (“Back of the envelop”) should be calculated for a
new system. The purpose is not to achieve high accuracy, but merely to determine if the
system is feasible. The calculation should be fast and should involve common sense.

Self Assessment

Fill in the blanks:
1. During system design the high-level of ........................ is chosen.

2. A thread of control is path through a set of ........................

LOVELY PROFESSIONAL UNIVERSITY 141