It's difficult to build a solution if you don't know the requirements (in spite of the fact that many teams still try to do it today). The "elicitation" step is where the requirements are first gathered from the client. Many techniques are available for gathering requirements. Each has value in certain circumstances, and in many cases, you need multiple techniques to gain a complete picture from a diverse set of clients and stakeholders. Here's a look at some of the approaches you can take.
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#1: One-on-one interviews
The most common technique for gathering requirements is to sit down with the clients and ask them what they need. The discussion should be planned out ahead of time based on the type of requirements you're looking for. There are many good ways to plan the interview, but generally you want to ask open-ended questions to get the interviewee to start talking and then ask probing questions to uncover requirements.
#2: Group interviews
Group interviews are similar to the one-on-one interview, except that more than one person is being interviewed -- usually two to four. These interviews work well when everyone is at the same level or has the same role. Group interviews require more preparation and more formality to get the information you want from all the participants. You can uncover a richer set of requirements in a shorter period of time if you can keep the group focused.
#3: Facilitated sessions
In a facilitated session, you bring a larger group (five or more) together for a common purpose. In this case, you are trying to gather a set of common requirements from the group in a faster manner than if you were to interview each of them separately.
#4: Joint application development (JAD)
JAD sessions are similar to general facilitated sessions. However, the group typically stays in the session until the session objectives are completed. For a requirements JAD session, the participants stay in session until a complete set of requirements is documented and agreed to.
Questionnaires are much more informal, and they are good tools to gather requirements from stakeholders in remote locations or those who will have only minor input into the overall requirements. Questionnaires can also be used when you have to gather input from dozens, hundreds, or thousands of people.
Prototyping is a relatively modern technique for gathering requirements. In this approach, you gather preliminary requirements that you use to build an initial version of the solution -- a prototype. You show this to the client, who then gives you additional requirements. You change the application and cycle around with the client again. This repetitive process continues until the product meets the critical mass of business needs or for an agreed number of iterations.
#7: Use cases
Use cases are basically stories that describe how discrete processes work. The stories include people (actors) and describe how the solution works from a user perspective. Use cases may be easier for the users to articulate, although the use cases may need to be distilled later into the more specific detailed requirements.
#8: Following people around
This technique is especially helpful when gathering information on current processes. You may find, for instance, that some people have their work routine down to such a habit that they have a hard time explaining what they do or why. You may need to watch them perform their job before you can understand the entire picture. In some cases, you might also want to participate in the actual work process to get a hands-on feel for how the business function works today.
#9: Request for proposals (RFPs)
If you are a vendor, you may receive requirements through an RFP. This list of requirements is there for you to compare against your own capabilities to determine how close a match you are to the client's needs.
On some projects, the requirements are not "uncovered" as much as they are "discovered." In other words, the solution is brand new and needs to be created as a set of ideas that people can agree to. In this type of project, simple brainstorming may be the starting point. The appropriate subject matter experts get into a room and start creatively brainstorming what the solution might look like. After all the ideas are generated, the participants prioritize the ones they think are the best for this solution. The resulting consensus of best ideas is used for the initial requirements.