System Engineering(part 1)

Introduction

System is an interrelated set of components, with an identifiable boundary, working together for some purpose.A system may include software, mechanical, electrical and electronic hardware and be operated by people.System components are dependent on other system components.Every system interacts with the environment through exchange of information.All systems come in hierarchies. Therefore, system exists to maintain its higher level systems.

The successful functioning of each system depends on the functioning of some other component.For example, software can only operate if the processor can only carry out computation if software system defining these computations has been successfully installed.

Types of System

a)Open System:A system that interacts freely with its environment, taking input and returning output.

b)Closed System:A system that is cut off from its environment and does not interact with it.

Characteristics of System

Components:An irreducible part or aggregation of parts that make up a system, also called subsystem.

Interrelated Components:Dependence of one subsystem on one or more subsystems.

Boundary:The line that marks the inside and outside of a system and that sets off the system from its environment.

Purpose:The overall goal or function of a system.

Environment:Everything external/internal to a system that interacts with the system known as system environment.

Interfaces:Point of contact where a system meets its environment or where subsystems meet each other.

Constraints:A limit to what a system can accomplish.

Input:Whatever a system takes from its environment in order to fulfill its purpose.

Output:Whatever a system returns to its environment in order to fulfill its purpose.

System Properties

a)Volume:The volume of system (total space occupied) varies depending on how the component assemblies are arranged and connected.

b)Usability:This property reflects how easily the system is to be used. It depends on the system component, its operator and its operating environment.

c)Security:The security of the system is complex property that cannot be easily measured. The security property of system depends on the design issue.

d)Repair ability:This property of system reflects how easily the problem in a system is to be fixed and removed. It depends on ability to diagnosis the problem and modifies or replaces components that cause problem.

e)Reliability:System reliability depends on component reliability unexpected interaction between components of the system. Component can cause new type of failure and affect the reliability of system.

System and Their Environment

• Systems are not independent but exist in an environment.
• System’s function may be to change its environment.
• Environment affects the functioning of the system e.g. system may require electrical supply from its environment.
• The organizational as well as the physical environment may be important.

System Engineering

Systems engineering is the activity of specifying, designing, implementing, validating, deploying and maintaining socio-technical systems.System engineers are not just concern with software but also with hardware, system interaction with users and its environment. They must think about the service that the system provides the constant under which the system must be built and operated and the way in which the system is used to fulfill its purpose.

Problems of System Engineering

• Large systems are usually designed to solve 'wicked' problems.
• Systems engineering requires a great deal of coordination across disciplines.

1. Almost infinite possibilities for design trade-offs across components.
2. Mutual distrust and lack of understanding across engineering disciplines.

• Systems must be designed to last many years in a changing environment.
• Missed schedule
• Improper integration of subsystems
• Maintenance problems
• Unmanageable systems

System Engineering Process

System engineering process is a set of activities whose goal is the development or evolution of software.Usually, It follows a ‘waterfall’ model because of the need for parallel development of different parts of the system , and little scope for iteration between phases because hardware changes are very expensive.
Software may have to compensate for hardware problems. It involves engineers from different disciplines who must work together.

A) Requirement Definition

System requirement definition specifies what the system should do and essential and desirable system property. The system requirement definition phase involves the consultation with the system customer and end user. The requirement definition phase usually concentrated on driving three types of requirements.

1. Abstract Functional Requirement:The basic function that the system must provide are defined at an abstract level. More detailed functional requirements specification takes place at the sub-system level.
2. System Properties:These are non-functional emergent system properties such as availability, performance, and safety. These properties affect the requirements for all sub-systems.
3. Characteristics:It is sometimes as important to specify what the system must not do as it is to specify what the system should do.

An important part of the requirements definition phase is to establish a set of overall objectives that the system should meet. These should not necessarily be expressed in terms of the system’s functionality but should define why the system is being procured for a particular environment.

System requirement problem:

• Changing as the system is being specified
• Must anticipate hardware/communications developments over the lifetime of the system
• Hard to define non-functional requirements particularly without an impression of component structure of the system

B) System Design

System design is concerned with how the system functionality is to be provided by the components of the systems. The activities involved in this process are:

1. Partition Requirements:Organise requirements into related groups.
2. Identify subsystems:Identify a set of sub-systems which collectively can meet the system requirements.
3. Assign requirements to subsystems:Here, the partitioned requirements are assigned to their respective subsystem.Also,Causes particular problems when COTS (Commercial Off-the-Shelf )are integrated.
4. Specify subsystem functionality:Specify the specific function provided by each sub-system and also try to identify relationships between subsystems.
5. Define subsystem interfaces:Critical activity for parallel sub-system development.

System design problem:

• Requirements partitioning to hardware, software and human components may involve a lot of negotiation.
• Difficult design problems are often assumed to be readily solved using software.
• Hardware platforms may be inappropriate for software requirements so software must compensate for this.

C) Subsystem 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

D) System Integration

• It is the process of putting hardware, software and people together to make a system
• It 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

E) System Installation

The organizational process of changing over from the current system to a new one. It has 4 approaches:

1. Direct installation:Changing over from the old system to a new one by turning off the old system when the new one is turned on.
2. Parallel installation:Running the old system and the new one at the same time until management decides the old system can be turned off.
3. Single location installation:Trying out a system at one site and using the experience to decide if and how the new system should be deployed throughout the organization.
4. Phased installation:Changing from the old system to the new one incrementally, starting with one or a few functional components and then gradually extending the installation to cover the whole new system.

Installation problem:

• Environmental assumptions may be incorrect
• May be human resistance to the introduction of a new system
• System may have to coexist with alternative systems for some time
• May be physical installation problems (e.g. cabling problems)
• Operator training has to be identified

F) System Evolution

Large, complex systems have a very long lifetime. They must evolve to meet changing requirements i.e. during their life, they are changed to correct errors in the original system requirements and to implement new requirements that have emerged.System Evolution is inherently costly ,like software evolution for several reasons:

• 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.

G)System Decommissioning

• It means taking the system out of service after its useful lifetime
• May require data to be restructured and converted to be used in some other system
• If the data in the system that is being decommissioned is still valuable to you organization or you may have to convert it for use by other systems.

Reference:

• Sommerville, Ian. Software engineering. eight edition. Newyork: pearson, 2007.
• coursehero. <https://www.coursehero.com/file/11487611/Chapter1-Introduction-to-Software-Engineering-cs/>.
• software engineering<https://books.google.com.np/books?id=CDWRq0B9e5kC&pg=PA5&lpg=PA5&dq=+Software+Software+is+computer+programs+and+associated+documentation.&source=bl&ots=fuFOT7wYOS&sig=0tkbWoER8gf7RxbScRjIQc7W_d0&hl=en&sa=X&redir_esc=y#v=onepage&q=Software Software is%>.
• csitprogram. .