Intended learning outcomes: Differentiate between system development and system implementation. In system development, present in detail the content of the preliminary study, the main study and the detailed studies. In system implementation, produce an overview on system establishment, system introduction and handover, system operation, and system decommission.
The system phases, or phases of life of a system, encompass three concept phases and four implementation phases as shown in Figure 19.1.0.1. The system life cycle comprises all of the life-cycle phases of a system.
In system development, there are three concept phases: Phase 1: The preliminary study, where the goal is, within a reasonable time frame, to acquire insights regarding:
- whether there exists a real need for a new system or modification of a system
- whether there exists a real need for a new system or modification of a system,
- whether the approach to the problem is correctly selected,
- what the boundaries of the given system are,
- what the most important functions of the system are, and
- what the principle solution variants for the problem are.
The client’s decision regarding feasibility and thus continuation or termination of the project and decision regarding the variants to be selected form the end of the preliminary study.
Phase 2: The main study, which comprises study of the whole system. If a subsystem can be assessed only with great difficulty, it can be necessary to conduct a detailed study already at this point. The result of the main study is a comprehensive concept of the system, and — depending on the type of system — it is in the form of a plan of tasks or activities, of construction plans, of a verbal description, or of other suitable means.
- With these results, it is now possible to make decisions regarding the investments, to define the subsystems, and set priorities in the realization of the detailed studies. Setting priorities is particularly important, as the task is now to evaluate and plan project resources (financial and human resources). In addition, it is necessary to first develop the important subsystems to which the less important subsystems are oriented. While this may reduce the degrees of freedom in the realization, it does accelerate the realization of the other subsystems, through, for example, possibly copying relevant subsystems developed first.
- The result of the main study may require a return to the previous concept phase, for example, if the requirements are not precise or not feasible.
Phase 3: Detailed studies. The result of detailed studies encompass, for one thing, the detailed concept for the subsystems and the final decision on the variants to be selected, and, for another, specification of the description of the individual part systems. The description will be precise enough to allow the system to be built without interpretation problems.
- There are various detailed studies, namely, of the individual subsystems and at different levels. So the next task is to reintegrate the individual systems, proceeding from the particular to the general (bottom up). Thus, the entire function and the interplay of the subsystems in their supersystems can be tested. This is a process that can reveal ways in which the detailed studies or also the main study should be modified.
During each of the concept phases, decisions must be made regarding the selection of the variants, end of the study, or return of the project to the next higher-level phase. Factors in these decisions are — in addition to the factors that relate to the functional objectives of the project — the expected costs and benefits. Costs and benefits often determine the variant that is to be selected among variants that appear to be equally good functionally. Or they may provide impetus to search for other variants, to terminate system development (the symbol Ω in Figure 19.1.0.1), or to continue on to the next life cycle phase of the system.
In system implementation, there are four life cycle phases. Phase 1: System establishment, describes elaboration of the system functions, for example:
- production of a machine and its documentation
- drawing up of a process or an organization
- coding and documentation of the programs in an IT-based information system
- elaboration of the organization to operate the system. In the example of an information system, what is needed are, among other things, documentation for the user, exact description of the procedures for data acquisition — especially from and to the surrounding systems — and the procedures for the use of information, actions to be taken in the case of system crisis, and training of users.
Phase 2: System introduction and handover is the transition to the production phase of the system. Often, especially with large projects, one subsystem is introduced after another, as there are always various unforeseeable factors to allow for. In this usually relatively short phase of introducing the system, systems corrections are often required that are very time critical. It is also possible to put some subsystems into operation while keeping others in the detailed concept phase, especially if the concept of the latter subsystems can be influenced by experience gained during operation of subsystems already introduced.
Phase 3: During system operation, there must be periodic and constructive review of the following points:
- Is the system really functioning as conceptualized? The answer to this question can serve as a source of experience for later, similar projects and provide the basis for a process of modification/correction.
- Are the commercial objectives being met as foreseen? Any deviations observed can aid improved assessment of costs and benefits in future projects.
Phase 4: Usually, the decision of system disposal, or of system decommission, is made concurrently with the introduction of a replacing system. For systems that are highly intertwined with daily operations, such as software systems at the operations level of a company, system replacement is often no light matter. Generally, the requirements are:
- that daily processes must not be interrupted for longer than a very short period;
- that the data should be transferred from the old system to the new system automatically, if possible.
System decommissioning for hardware systems (e.g., computers, terminals) involves physical disposal of the single components. This can be a big challenge, both technically and in terms of costs. Thus, system disposal should be a part of systems engineering from the start.
If the system will be in operation for a certain period of time only, all of the life cycle phases of the system can be seen as and conducted as one single project. Otherwise, the concept phases can be taken together with elaboration of the system and introducing the system as one project, and system decommissioning as a new project.
Course section 19.1: Subsections and their intended learning outcomes
19.1 Systems Engineering
Intended learning outcomes: Explain systems thinking and the top-down approach. Describe phases of life of a system and the system life cycle. Present in detail the problem solving cycle. Disclose the differences between software engineering and classical systems engineering.
19.1.1 Systems Thinking and the Top-Down Approach
Intended learning outcomes: Describe systems thinking and the proceeding from the general to the particular (top-down approach). Produce an overview on creating and evaluating variants at each level of the system.
19.1.2 Phases of Life of a System and System Life Cycle
Intended learning outcomes: Differentiate between system development and system implementation. In system development, present in detail the content of the preliminary study, the main study and the detailed studies. In system implementation, produce an overview on system establishment, system introduction and handover, system operation, and system decommission.
19.1.3 The Problem Solving Cycle
Intended learning outcomes: Identify the problem-solving cycle. Present in detail situational analysis, formulation of objectives, synthesis of solutions, analysis of solutions, evaluation of solutions, and decision in the problem-solving cycle.
19.1.4 The Waterfall Model Versus the Spiral Model
Intended learning outcomes: Describe system development by strictly following to sequence of life cycle phases and the waterfall model. Explain iterative system development, prototyping and the spiral model.
