Assignment3_612_std49532

Name Aye Thida

Roll No EMCS-980
Assignment 3

(a) Describe the phases of the system engineering process.

The phases of the System engineering process

Requirements System
definition decommissioning

System System
Design evolution

Sub- system System

development Installation

System
Integration

Requirements definition

Three types of requirement defined at this stage

 Abstract functional requirements. System functions are defined in an abstract way

 System properties. Non-functional requirements for the system in general are defined
 Undesirable characteristics. Unacceptable system behavior is specified

Page 1 of 5
Assignment3_612_std49532

System design

Partition requirements
• Organise requirements into related groups
Identify sub-systems
• Identify a set of sub-systems which collectively can meet the system requirements
Assign requirements to sub-systems
• Causes particular problems when COTS are integrated
Specify sub-system functionality
Define sub-system interfaces
• Critical activity for parallel sub-system development

Sub-system development

 Typically parallel projects developing the hardware, software and communications

 May involve some COTS (Commercial Off-the-Shelf) systems procurement
 Lack of communication across implementation teams
 Bureaucratic and slow mechanism for proposing system changes means that the
development schedule may be extended because of the need for rework

System Integration

 The process of putting hardware, software and people together to make a system
 Should be tackled incrementally so that sub-systems are integrated one at a time
 Interface problems between sub-systems are usually found at this stage
 May be problems with uncoordinated deliveries of system components

System Installation

 Environmental assumptions may be incorrect

 May be human resistance to the introduction of a new system
 System may have to coexist with alternative May be physical installation problems (e.g.
cabling problems)
 Operator training has to be identified

Page 2 of 5
Assignment3_612_std49532

System evolution

 Large systems have a long lifetime. They must evolve to meet changing requirements
 Evolution is inherently costly
- Changes must be analyzed from a technical and business perspective
- Sub-systems interact so unanticipated problems can arise
- There is rarely a rationale for original design decisions
- System structure is corrupted as changes are made to it
 Existing systems which must be maintained are sometimes called legacy systems

System decommissioning

 Taking the system out of service after its useful lifetime

 May require removal of materials (e.g. dangerous chemicals) which pollute the environment
- Should be planned for in the system design by encapsulation
 May require data to be restructured and converted to be used in some other system

Page 3 of 5
Assignment3_612_std49532

(b) The emergent properties of a system are properties that are characteristics of the
system as a whole rather than of its component parts. Do you agree that the success or
failure of a system is often dependent on these emergent properties? Why?

The Emergent Properties are:

1) Properties of the system as a whole rather than properties than can be derived from the
properties of components of a system
2) Emergent properties are a consequence of the relationships between system components
3) They can therefore only be assessed and measured once the components have been
integrated into a system

Two Types of Emergent Properties are:

1) Functional properties
 These appear when all the parts of the system work together to achieve some
objective.
2) Non-Functional properties
 Reliability, performance, safety, and security are related to the behavior of the
system in its operational environment. They are often critical for computer-based
systems as failure achieve some minimal defined level in these properties may
make the system unusable.

Example of Emergent Properties:

Reliability depends on the reliability of the system components and the relationships
between the components.

Security is a complex property that cannot be easily measured. Attacked may be de

devised that were not anticipated by the system designers and so may
defeat built-in safeguard.

Usability is a complex property which is not simply dependent on the system

hardware and software but also depends on the system operators and the
environment where it is used.

By seeing the above points, Emergent properties are properties that are characteristic of the
system as a whole and not its component parts. Therefore, I agree that the success or failure
of a system is often dependent on these emergent properties.

Page 4 of 5
Assignment3_612_std49532

(c) Explain why legacy systems can cause difficulties for companies that wish to
reorganize their business processes.

Legacy System are socio-technical computer-based systems that have been developed in the
past, often using older or obsolete technology. These systems include not only hardware and
software but also legacy process and procedures old ways of doing things.

1) System Hardware In many cases, legacy system have been written for main frame
hardware that is no longer available, that is expensive to maintain and that may not be
compatible with current organizational IT purchasing policies.
2) Support Software The Legacy system may rely on a range of support software from
the operating system and utilities provided by the hardware manufacturer through to the
compilers used for system development.
3) Application Software The application system that provides the business services is
usually composed of a number of separate programs that have been developed at different
times. Sometimes the term legacy system means this application software system rather
than the entire system.
4) Application data These the data that are processed by the application system. This
data may be inconsistent and may be duplicated in several files.
5) Business processes These are processes that are used in the business to achieve some
business objective. Business processes may be designed around a legacy system and
constrained by the functionality that it provides.
6) Business policies and rules These are definitions of how the business should be carried
out and constraints on the business. Use of the legacy application system may be
embedded in these policies and rules.

So Legacy systems can cause difficulties for companies that wish to recognize their business
processes because they are old systems that still provide essential business services and there
are complex interactions between the processes of the system procurement, development and
operation.

Page 5 of 5