Software Engineering-Requirements Elicitation For Software


Before requirements can be analyzed, modeled, or specified they must be gathered through an elicitation process. A customer has a problem that may be amenable to a computer-based solution. A developer responds to the customer's request for help. Communication has begun. But, as we have already noted, the road from communication to understanding is often full of potholes.

Initiating the Process

The most commonly used requirements elicitation technique is to conduct a meeting or interview. The first meeting between a software engineer (the analyst) and the customer can be likened to the awkwardness of a first date between two adolescents. Neither person knows what to say or ask; both are worried that what they do say will be misinterpreted; both are thinking about where it might lead (both likely have radically different expectations here); both want to get the thing over with, but at the same time, both want it to be a success.

Yet, communication must be initiated. Gause and Weinberg  suggest that the analyst start by asking context-free questions. That is, a set of questions that will lead to a basic understanding of the problem, the people who want a solution, the nature of the solution that is desired, and the effectiveness of the first encounter itself. The first set of context-free questions focuses on the customer, the overall goals, and the benefits. For example, the analyst might ask:
Who is behind the request for this work?
Who will use the solution?
What will be the economic benefit of a successful solution?
Is there another source for the solution that you need?

These questions help to identify all stakeholders who will have interest in the software to be built. In addition, the questions identify the measurable benefit of a successful implementation and possible alternatives to custom software development. The next set of questions enables the analyst to gain a better understanding of the problem and the customer to voice his or her perceptions about a solution:
How would you characterize "good" output that would be generated by a successful solution?
What problem(s) will this solution address?
Can you show me (or describe) the environment in which the solution will be used?
Will special performance issues or constraints affect the way the solution is
approached?

The final set of questions focuses on the effectiveness of the meeting. Gause and Weinberg  call these meta-questions and propose the following (abbreviated) list:
Are you the right person to answer these questions? Are your answers "official"?
Are my questions relevant to the problem that you have?
Am I asking too many questions?
Can anyone else provide additional information?
Should I be asking you anything else?

These questions (and others) will help to "break the ice" and initiate the communication that is essential to successful analysis. But a question and answer meeting format is not an approach that has been overwhelmingly successful. In fact, the Q&A session should be used for the first encounter only and then replaced by a meeting format that combines elements of problem solving, negotiation, and specification. An approach to meetings of this type is presented in the next section.

Facilitated Application Specification Techniques

Too often, customers and software engineers have an unconscious "us and them" mind-set. Rather than working as a team to identify and refine requirements, each constituency defines its own "territory" and communicates through a series of memos,formal position papers, documents, and question and answer sessions. History has shown that this approach doesn't work very well. Misunderstandings abound, important information is omitted, and a successful working relationship is never established.

It is with these problems in mind that a number of independent investigators have developed a team-oriented approach to requirements gathering that is applied during early stages of analysis and specification. Called facilitated application specification techniques (FAST), this approach encourages the creation of a joint team of customers and developers who work together to identify the problem, propose elements of the solution, negotiate different approaches and specify a preliminary set of solution requirements. FAST has been used predominantly by the information systems community, but the technique offers potential for improved communication in applications of all kinds.

Many different approaches to FAST have been proposed. Each makes use of a slightly different scenario, but all apply some variation on the following basic guidelines:

A meeting is conducted at a neutral site and attended by both software engineers and customers.
Rules for preparation and participation are established.
An agenda is suggested that is formal enough to cover all important points but informal enough to encourage the free flow of ideas.
A "facilitator" (can be a customer, a developer, or an outsider) controls the meeting.
A "definition mechanism" (can be work sheets, flip charts, or wall stickers or an electronic bulletin board, chat room or virtual forum) is used.
The goal is to identify the problem, propose elements of the solution, negotiate different approaches, and specify a preliminary set of solution requirements in an atmosphere that is conducive to the accomplishment of the goal.

To better understand the flow of events as they occur in a typical FAST meeting, we present a brief scenario that outlines the sequence of events that lead up to the meeting, occur during the meeting, and follow the meeting.

Initial meetings between the developer and customer  occur and basic questions and answers help to establish the scope of the problem and the overall perception of a solution. Out of these initial meetings, the developer and customer write a one- or two-page "product request." A meeting place, time, and date for FAST are selected and a facilitator is chosen. Attendees from both the development and customer/user organizations are invited to attend. The product request is distributed to all attendees before the meeting date.

While reviewing the request in the days before the meeting, each FAST attendee is asked to make a list of objects that are part of the environment that surrounds the system, other objects that are to be produced by the system, and objects that are used by the system to perform its functions. In addition, each attendee is asked to make another list of services (processes or functions) that manipulate or interact with the objects. Finally, lists of constraints (e.g., cost, size, business rules) and performance criteria (e.g., speed, accuracy) are also developed. The attendees are informed that the lists are not expected to be exhaustive but are expected to reflect each person’s perception of the system.

As an example, assume that a FAST team working for a consumer products company has been provided with the following product description:

Our research indicates that the market for home security systems is growing at a rate of 40 percent per year. We would like to enter this market by building a microprocessor-based home security system that would protect against and/or recognize a variety of undesirable "situations" such as illegal entry, fire, flooding, and others. The product, tentatively called SafeHome, will use appropriate sensors to detect each situation, can be programmed by the homeowner, and will automatically telephone a monitoring agency when a situation is detected.

In reality, considerably more information would be provided at this stage. But even with additional information, ambiguity would be present, omissions would likely exist, and errors might occur. For now, the preceding "product description" will suffice. The FAST team is composed of representatives from marketing, software and hardware engineering, and manufacturing. An outside facilitator is to be used.

Each person on the FAST team develops the lists described previously. Objects described for SafeHome might include smoke detectors, window and door sensors, motion detectors, an alarm, an event (a sensor has been activated), a control panel, a display, telephone numbers, a telephone call, and so on. The list of services might include setting the alarm, monitoring the sensors, dialing the phone, programming the control panel, reading the display (note that services act on objects). In a similar
fashion, each FAST attendee will develop lists of constraints (e.g., the system must have a manufactured cost of less than $80, must be user-friendly, must interface directly to a standard phone line) and performance criteria (e.g., a sensor event should be recognized within one second, an event priority scheme should be implemented).

As the FAST meeting begins, the first topic of discussion is the need and justification for the new product—everyone should agree that the product is justified. Once agreement has been established, each participant presents his or her lists for discussion. The lists can be pinned to the walls of the room using large sheets of paper, stuck to the walls using adhesive backed sheets, or written on a wall board. Alternatively, the lists may have been posted on an electronic bulletin board or posed in a chat room environment for review prior to the meeting. Ideally, each list entry should be capable of being manipulated separately so that lists can be combined, entries can be deleted and additions can be made. At this stage, critique and debate are strictly prohibited.

After individual lists are presented in one topic area, a combined list is created by the group. The combined list eliminates redundant entries, adds any new ideas that come up during the discussion, but does not delete anything. After combined lists for all topic areas have been created, discussion—coordinated by the facilitator—ensues. The combined list is shortened, lengthened, or reworded to properly reflect the product/ system to be developed. The objective is to develop a consensus list in each topic area (objects, services, constraints, and performance). The lists are then set aside for later action.

Once the consensus lists have been completed, the team is divided into smaller subteams; each works to develop mini-specifications for one or more entries on each of the lists. Each mini-specification is an elaboration of the word or phrase contained on a list. For example, the mini-specification for the SafeHome object control panel might be

mounted on wall
size approximately 9 x 5 inches
contains standard 12-key pad and special keys
contains LCD display of the form shown in sketch [not presented here]
all customer interaction occurs through keys
used to enable and disable the system
software provides interaction guidance, echoes, and the like
connected to all sensors

Each subteam then presents each of its mini-specs to all FAST attendees for discussion. Additions, deletions, and further elaboration are made. In some cases, the development of mini-specs will uncover new objects, services, constraints, or performance requirements that will be added to the original lists. During all discussions, the team may raise an issue that cannot be resolved during the meeting. An issues list is maintained so that these ideas will be acted on later.

After the mini-specs are completed, each FAST attendee makes a list of validation criteria for the product/system and presents his or her list to the team. A consensus list of validation criteria is then created. Finally, one or more participants (or outsiders) is assigned the task of writing the complete draft specification using all inputs from the FAST meeting.

FAST is not a panacea for the problems encountered in early requirements elicitation. But the team approach provides the benefits of many points of view, instantaneous discussion and refinement, and is a concrete step toward the development of a specification.
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