Socio-technical Systems (Computer-based System Engineering) Chapter 2 Socio-technical Systems (Computer-based System Engineering)

System Engineering Is the activity of specifying, designing, implementing, deploying, maintaining systems, which include hardware, software , people and interaction of the system with users and its environment.

Objectives To introduce the concept of emergent system properties such as reliability and security To explain system engineering and system processes

What is a system? A collection of inter-related components working together towards some common objective. A system may include software, mechanical, electrical and electronic hardware and be operated by people. System components are dependent on other system components System is more than simply the sum of its parts! It has properties of the system as a whole. (emergent properties)

Socio-technical system characteristics They have emergent properties Properties of the system of a whole that depend on the system components and their relationships. They are often Non-deterministicغير قطعية They do not always produce the same output when presented with the same input because the system’s behaviour is partially dependent on human operators.

System categories , cont… Technical computer-based systems Systems that include hardware and software but where the operators and operational processes are not normally considered to be part of the system. Socio-technical systems Systems that include technical systems but also operational processes and people who use and interact with the technical system. Socio-technical systems are governed by organizational policies and rules.

Problems of systems engineering Large systems are usually designed to solve 'wicked' problemsالشرس Systems engineering requires a great deal of coordination across disciplines distrust and lack of understanding across engineering disciplines Systems must be designed to last many years in a changing environment

Emergent System properties Properties of the system as a whole rather than properties that can be derived from the properties of components of a system. Emergent properties are a consequence (result) of the relationships between system components They can therefore only be assessed and measured ONCE the components have been integrated into a system

Examples of emergent properties

Types of emergent properties Functional properties These appear when all the parts of a system work together to achieve some objective. For example, a bicycle has the functional property of being a transportation device once it has been assembled from its components.

Types of emergent properties (cont.) Non-functional emergent properties Examples are reliability, performance, safety, and security. These relate to the behaviour of the system in its operational environment. They are often critical for computer-based systems as failure that may make the system unusable.

Complexity of emergent system properties- reliability Because of component inter-dependencies, faults can be propagated through the system, so failure in one component can affect the operation of other components. System failures often occur because of unforeseen inter-relationships between component.

Influences on a system reliability Hardware reliability What is the probability of a hardware component failing and how long does it take to repair that component? Software reliability How likely is it that a software component will produce an incorrect output. Software failure is usually distinct from hardware failure in that software does not wear out. Operator reliability How likely is it that the operator of a system will make an error?

Influences on a system reliability (cont.) Properties such as performance, usability, and reliability are difficult to assess but can be measured after the system is operational. However, some properties such as safety and security pose a different problem, because it is very hard to predict all possible modes of access and explicitly forbid them. Safety - the system that reflects the system’s ability to operate without danger Security - the system should not permit unauthorised use Measuring or assessing these properties is very hard (why???)

The system engineering process Usually follows a ‘waterfall’ model because of the need for development of different parts of the system. There are important distinctions between the system engineering process and the software development process:

The system engineering process (cont.) Little scope for rework during system development because hardware changes are very expensive, reworking the system design to solve these problems. Software becomes so important in systems because of its flexibility Example: siting of Base station in mobile cell Always involves engineers from different disciplines , many engineering disciplines who must work together, much scope for misunderstanding here. Different disciplines use a different vocabulary and much negotiation is required. Engineers may have personal agendas to fulfil.

The system engineering process (cont.)

Inter-disciplinary involvement Air traffic control