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Requirements Management

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Software requirements engineering is a process of discovery, refinement, modeling and specification. The system requirements and role allocated to software-initially established by the system engineer-are refined in detail. Models of the required data information and control flow and operational behavior are created. Alternative solutions are analyzed and a complete analysis model is created.

Requirements engineering is the systematic use of proven principles, techniques, languages, and tools for the cost effective analysis, documentation, and on-going evolution of user needs and the specification of the external behavior of a system to satisfy those user needs. Notice that like all engineering disciplines, requirements engineering is not conducted in a sporadic random or otherwise haphazard fashion, but instead is the systematic use of proven approaches.

Both the software engineer and customer take an active role in software requirements engineering-a set of activities that is often referred to as analysis. The customer attempts to reformulate a sometimes nebulous system-level description of data, function and behavior into concrete detail. The developer acts as interrogator, consultant, problem solver and negotiator.

The overall role of Software in a larger system is identified during system engineering. However, it’s necessary to take a harder look at software’s role-to understand the specific requirements that must be achieved to build high-quality software. That’s the job of software requirements analysis. To perform the job properly, you should follow a set of underlying concepts and principles. Generally, a software engineer performs requirements analysis However, for complex business applications a ‘system analyst’ trained in the business aspects of the application domain may perform the task. If you don’t analyze, it’s highly likely that you’ll build a very elegant software solution that solves the wrong problem. The result is wasted time and money, personal frustration and unhappy customers.

Data, functional, and behavioral requirements are identified by eliciting information from the customer. Requirements are refined and analyzed to assess their clarity, completeness, and consistency.

⇒ Requirements analysis

Requirements analysis is a software engineering task that bridges the gap between system level requirements engineering and software design (Figure 1). Requirements engineering activities result in the specification of software’s operational characteristics (function, data; and behavior), indicate software’s interface with other system elements, and establish constraints that software must meet. Requirements analysis allows the software engineer (sometimes called analyst in this. role) to refine the software allocation and build models of the data, functional, and behavioral domains that will be treated by software. Requirements analysis provides the software designer with a representation of information, function, and behavior that can be translated to data, architectural, interface, and component-level designs. Finally, the requirements specification provides the developer and the customer with the means to assess quality once software is built.

Figure 1: a bridge between system engineering and software design

Software requirements analysis may be divided into five areas of effort:

(1) Problem recognition,

(2) Evaluation and synthesis,

(3) Modeling

(4) Specification, and

(5) Review

Initially, the analyst studies the System Specification (if one exists) and the Software Project Plan. It is important to understand software in a system context and to review the software scope that was used to generate planning estimates. Next, communication for analysis must be established so that problem recognition is ensured. The goal is recognition of the basic problem elements as perceived by the customer/users.

• Problem evaluation

Problem evaluation and solution synthesis is the next major area of effort for analysis. The analyst must define all externally observable data objects, evaluate the flow and content of information, define and elaborate all software functions, understand software behavior in the context of events that affect the system, establish system interface characteristics, and uncover additional design constraints. Each of these tasks serves to describe the problem so that an overall approach or solution may be synthesized. For example, an inventory control system is required for a major supplier of auto parts. The analyst finds that problems with the current manual system include:

(1) Inability to obtain the status of a component rapidly

(2) Two or three-day turnaround to update a card file

(3) Multiple reorders to the same vendor because there is no way to associate vendors with components, and so forth.

Once problems have been identified, the analyst determines what information is to be produced by the new system and what data will be provided to the system. For instance, is the customer desires a daily report that indicates what parts have been taken from inventory and how many similar parts remain. The customer indicates that inventory clerks will log the identification number of each part as it leaves the inventory area.

• Solution synthesis

Upon evaluating current problems and desired information (input and output), the analyst begins to synthesize one or more solutions. To begin, the data objects processing functions and behavior of the system are defined in detail. Once this information has been established, basic architectures for implementation are considered.

A client/server approach would seem to be appropriate, but does the software to support this architecture fall within the scope outlined in the Software Plan? A database management system would seem to be required, but is user/customer’s need for associativity justified? The process of evaluation and synthesis continues until both analyst and customer feel confident that software can be adequately specified for subsequent development steps.

Throughout evaluation and solution synthesis, the analyst’s primary focus is on “what, not “how.” What data does the system produce and consume what functions the system must perform. What behaviors do the system exhibit, what interfaces, are defined and what constraints apply?

During the evaluation and solution synthesis activity, the analyst creates models of the system in an effort to better understand data and control flow, functional processing, operational behavior, and information content. The model serves as a foundation for software design and as the basis for the creation of specifications for the Software. The customer may be unsure of precisely what is required. The developer may be unsure that a specific approach will properly accomplish function and performance. For these, and many other reasons, an alternative approach to requirements analysis, called Prototyping, may be conducted.