System life cycle

System Planning--

The system planning is the first stage of the information system life cycle, its task is to carry on the preliminary investigation to the enterprise's environment, the goal and the existing system's condition, according to the enterprise goal and the development strategy, determines the information system development strategy, makes the analysis and the forecast to the construction new system's demand, simultaneously considers constructs the new system the various constraints, To study the necessity and possibility of building a new system. An alternative to the proposed system is given, as needed and possible. The feasibility analysis of these schemes is carried out and the feasibility study report is written. After the feasibility study report is passed, the new system construction plan and implementation plan are written into the system design task book.

The construction of information system is a social technology project with large investment, long cycle and high complexity. System planning can reduce blindness, so that the system has a good overall, high adaptability, construction work has a good stage to shorten the system development cycle, save development costs. At present, the domestic enterprise construction information System, single application of more, comprehensive application of less, system adaptability is poor, difficult to expand. Lack of scientific planning is one of the reasons for this phenomenon, some large-scale projects, because there is no systematic planning and scientific argumentation, the launch of the vigorous, after the difficulties, leading to Tiger situation, not only caused the huge waste of capital, manpower, but also for the future of the system to leave hidden trouble. Therefore, system planning is the key to the achievement of information system construction, which is more important than the development of concrete projects.

System Analysis--

The system analysis stage is also called the logic design stage, its task is to carry on the detailed investigation to the existing system according to the scope of the system design task book, describe the business process of the existing system, point out the limitation and insufficiency of the existing system, determine the basic goal and the logic function requirement of the new system, and put forward the new system logic model.

In the system analysis stage, the system analyst and the user to carry on the investigation and analysis carefully, the user's initial requirement concrete, the explicit, finally transforms the new system "does what" the logical model. System analysis is the key stage of the whole system construction, and it is also the important difference between the construction of information system and the general project. The work results of the system analysis stage are embodied in the System Requirement Specification , which is the necessary document of system construction, the basis of the system design stage and the basis of the future system acceptance.

Software Requirements Engineering--

At the beginning of computer development, software is small, software development is concerned with code writing, demand analysis is seldom paid attention to. Later, software development introduced the concept of life cycle, demand analysis became its first stage. With the enlargement of the system scale, the requirement analysis and definition are more and more important in the whole system development and maintenance process, which is directly related to the result of the system. There is also a growing recognition that demand analysis activities are no longer confined to the initial stages of system development, but throughout the life cycle of system development. So, the sub-domain of software engineering is formed.

Software Requirements Engineering is a process that includes all the activities necessary to create and maintain a software requirements document, which can be divided into two major tasks: demand development and demand management. Requirements development includes requirements acquisition, demand analysis, writing requirements specification (requirements definition), and 4 phases of requirements validation. During the requirements development phase, you need to identify the types of users your software expects, get the needs of each type of user, understand the actual user tasks and goals, and the business requirements that these tasks support. It also includes the analysis of information originating from users, prioritizing requirements, and compiling the collected requirements into requirements baselines, processing requirements changes, and tracking requirements. These two aspects are mutually reinforcing, the demand development is the main line, is the goal, the demand management is the support, is the safeguard.

Software Architecture Design--

The traditional software development process can be divided into several stages from concept to implementation, including software planning, requirement analysis, software design, software implementation and software testing. In this development process, how to transform the results of demand analysis into software design, this problem has been plagued by researchers and practitioners. In recent years, the software engineering industry has put forward a variety of requirements engineering and software modeling technology, however, there is still a difficult gap between software requirements and design, so it is difficult to effectively convert the requirements to the corresponding design. To this end, the scholars put forward the concept of software architecture (software Architecture), and try to bridge the software requirements and design, focusing on solving the problem of system structure and demand to achieve flat over.

On the other hand, as software systems become larger and more complex, the structure and specifications of the system are becoming more and more important. In this context, people also gradually realize the importance of software architecture, and promote the rapid development and application of software architecture technology.

System Design--

System design is the extension and expansion of system analysis. The system analysis phase solves the problem of "what to do", while the system design phase solves the problem of "how to Do". At the same time, it is also the basis for the implementation of the system to pave the groundwork for the implementation. Reasonable system design scheme can not only guarantee the quality of the system, but also improve the efficiency of system development and ensure the smooth implementation of the system.

The system design stage is also called the physical design stage, it is a very important stage in the information system development process. Its task is based on the functional requirements stipulated in the system specifications, considering the actual conditions, the specific design of the implementation of the logical model of the technical plan, that is, the design of the new system of the physical model, for the next stage of the implementation of the system to lay the foundation.

System implementation and testing--

The system implementation phase is the process of putting the design system into practice. This phase of the task includes the acquisition of computers and other equipment, equipment installation and commissioning, program preparation and commissioning, personnel training and so on. This stage is characterized by a number of interrelated and mutually constrained tasks at the same time, therefore, must be carefully arranged and reasonable organization. The implementation of the system is carried out in stages according to the implementation plan, each stage should write the implementation progress report, after the system test write test Analysis report.

The quality of system is closely related to the quality of system analysis and design, but the program design method, programming language and program design style of system implementation will have a great influence on the reliability, maintainability and reusability of the system. Software testing is one of the main means of software quality assurance, and its purpose is to identify as many errors and defects in software as possible before the software is formally run.

System operation and Maintenance--

After the system planning, analysis, design, implementation and testing, the expected information system has been developed, can be delivered to the user's use. In the process of information system operation, there will still be hidden errors not found in the system debugging and testing stage, but also may be the system changes for the expansion and integration of the system functions, in order to maintain and manage the system scientifically, record the operation of the system, and evaluate the quality and economic benefits of the system. This is a long-term work, according to the actual situation of the information systems, the system operation and maintenance phase in the entire department life cycle of the proportion of 60%~80%.

System life cycle