System Requirements Analysis
Requirements analysis is a very important stage in the software life cycle. Because developers are familiar with computers but not
business in the application domain, and users are familiar with business in the application domain but not computers, there
may be differences in understanding between developers and users for the same problem. In the requirements analysis stage, through extensive communication between developers and users, some vague concepts are constantly clarified, and finally a complete , clear and consistent requirement description is formed. It can be said that the quality of requirements analysis
will directly affect the success or failure of the developed software.
1 Tasks of needs analysis
Requirements analysis is mainly to determine the function , performance , data and interface requirements of the software to be developed . Specifically, there can be the following
five aspects:
- Determine the comprehensive requirements of the software system , mainly including system interface requirements, system function requirements, system performance requirements
, system security and confidentiality requirements, system reliability requirements, system operation requirements, exception handling requirements and possible future
requirements. - Analyze the data requirements of the software system , including basic data elements, logical relationships between data elements, data volume and
peak value, etc. The commonly used data description method is the entity-relationship model ( ER model ). - Create a logical model of the system . In the structural analysis method, it can be described by a data flow diagram; in the object-oriented analysis method,
it can be described by a class model. - Revised project development plan . After clarifying the real needs of users, the cost and progress of the software can be estimated more accurately
, so as to revise the project development plan. - A prototype system can be developed if necessary. For some software whose requirements are not clear enough, a prototype
system can be developed first to verify the user's requirements.
What needs to be emphasized here is that the requirements analysis stage mainly solves the "do what" , and "how to" is
done by the design phase.
2 Classification of needs
Software requirements are what the system must accomplish and the qualities it must possess . Software requirements includeFunctional Requirements、non-functional
requirementsanddesign constraintsthree aspects.
- Functional requirements : What kind of functions must the developed software have, which can be shown in structured functional documents.
- Non-functional requirements : Refers to the attributes or qualities that a product must have, such as reliability, performance, response time, fault tolerance,
and scalability. - Design Constraints : Also known as constraints, supplementary specifications, which are usually some constraints on the solution.