Hitchhiker's Guide to Software Architecture and Everything Else - by Michael Stal

Sunday, January 21, 2007

How to start with requirements

Often when I am involved in software development projects as a software architecture consultant, team members are wondering how to start in terms of requirements engineering and how to proceed once all the requirements are available. As this is an issue that is critical for project success, I will elaborate on it in this and upcoming postings. Note however, I won't cover tools such as DOORS, or IBM/Rational. Here is my short take on this, tools in a nutshell if you wish so. Michael's rule of tool usage: Tools are relevant iff they give more support than they incur trouble :-;

So, let us assume we are starting a new project. For simplicity, suppose we are in a company that produces healtcare products. Some senior managers in our company found out that it is time to build a web-based framework for physicians where patients can obtain information, ask for prescriptions online and arrange meeting schedules. Product management asked several customers for theirs required and desired features and it turned out that customers would buy such kind of product. Thus, we got our business case.

As a software architect, the first step is to interview stakeholders about their requirements. The problem here is that senior managers and product managers are often far away from software architecture and technology. Hence, it is our task to clarify requirements with them and translate management level requirements to technical requirements. For example, I often hear sentences such as "this must be performant and scalable and secure and flexible." Yes, but what exactly do they mean by "flexible" or by "performant"? What if both requirements contradict each other? Another issue here is that different stakeholders often have different perspectives. A project manager in a multi-site software development project might be more interested to partition subsystems in such a way that each subsystem is developed by only one site, while a software architect thinks more problem-space oriented. Political issues might also be lurking such as sites which are striving for being responsible for specific parts of the product. Obviously, outsourcing and offshoring denote important factors as well. All of these issues need to be addressed by software architects. In order to deal with them, architects must disclose the relevant issues from day one. Here, it turns out how important communication skills are for architects if you ever doubted it.
My first recommendation is: software architects should arrange meetings where they interview all relevant stakeholders. Thus, identify stakeholders with senior management. Then take the time to interview all of these stakeholders. Prepare yourself with checklists where you list questions you want to ask the stakeholders. Otherwise, it might be a problem to get full coverage or to obtain comparable answers. Note, that these checklists differ depending on the personal backgrounds of interviewees. It is a common rule that senior managers only seldomly can give technology or architecture advice (at least not explicitely). In the interviews clarify requirements. Ask interviewees what they exactly mean with the requirements. You should also be prepared to ask more concrete questions and guide the interviews. For example: our online patient system framework should be flexible. What does flexible mean - parts can be removed, added, exchanged, removed or does it refer to modularity? How fast must changes be committed? How many changes are anticipated? Can these changes be added at runtime or at compile time or at maintenance time? What kind of changes do typically occur? Don't forget to ask interviewees about the priorities they give these requirements. If they tell you, all requirements are of identical importance, ask them questions like: "If you had to choose one of these requirements as the most importan one what would it be?" or "What are the features that must be available in the beginning and what do you consider the highest risk?".
After the interviews set up a kick off meeting where all architects and stakeholders are invited. Present your findings to them and also prepare a rough proposal of the project setup (milestones, work packages, activities, requuirements with priorities and risks). After the meeting all the attendees should commit to a final project plan, have a common understandings of terms, and what exactly the requirements mean, and what their risks and priorities are.
In this context, it is important to mention that there are different types of requirements:
  • Functional requirements define the concrete domain-specific problem (in terms of the problem space not of the solution space!). Here a DSL is a good start. Or at least, should be one of the results of domain modelling.
  • Operational requirements such as performance or fault tolerance relate to the operation of the final product.
  • Developmental requirements define architectural issues such as flexibility.

Customers are often more interested in functional and operational qualities. These qualities will also have a huge impact on the strategic core of your product. Developmental qualities are mostly tactical issues. They are of high relevance for the development team, especially when we are going to build a product line such as in our example project.

Often, it helps a lot when defining the boundaries of the system to be built using context diagrams. Additionally, a use case analysis with participation by customers is essential.

It is important to mention that a software product line such as the one introduced in our running example requires special focus on commonalities and variabilities of the products we are going to build. For example, some of our customers might need the patient meetings to be synchronized with Exchange Server, while others might use IBM/Lotus, or even exotic platforms. Thus, our patient framework must be built in a way that allows this kind of variability. Another variability may be the different looks and feels of the Web sites.

After you got final agreement and committment on the requirements you can start to proceed to the next step and set up the project which won't be covered in my postings. However, it turns out to be important to asign important subsystems to key developers and also assign the most important non-functional issues also to key developers. Software architects are then responsible for the whole picture, but key developers for their own topic of concern. In the beginning, architects and (and key developers) will design a base line architecture and communicate this architecture to the stakeholders. The design should reflect functional aspects but also at least the core non-functional concerns.

In our example, security and usability will be most likely the most important requirements. Thus, we should organize two teams, one responsible for security and the other one for usability.

In the whole project activities is essential to ensure requirement traceability. Each design or implementation decision should be motivated by requirements and follow the architectural baseline. This is where architects must act as supervisors.

This concludes the first posting in my "series".


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