Know thy domain!


Let’s assume you are hired to develop a software system for a pharmaceutical company. Till that time, you knew nothing about that specific domain, no more than everybody knows about the pharmaceutical sector and medicines.And the knowledge you carry is from the side of the patient-client.

You start gathering information to build the requirements, but you come to point that you feel ready to start writing code. Well, don’t hurry that much. Are you sure the information you have in your hands is right, and at the same time is the one you actually need?

Lack of domain expertise

Programmers, unfortunately, sometimes change domains a lot. Take for example! I was working for a company that develops HR and payroll software, and now I work for European funded R&D projects related to Industry 4.0. Far from similar. But no matter what I have to adapt, to learn and be productive as fast as possible.

In the agile world, the product owner represents a range of stakeholders, not just end users, and in practice it isn’t reasonable to expect them to be experts at everything in the domain. As a result the product owner will bring in domain experts to work with the team. The programmers responsibility is to be open minded and learn from every word information that comes from the expert. Also don’t be a “know all” person. Trust the domain expert and work with them.

Understanding the domain helps you design a better software. A software with the expected, by the stakeholders, behavior as the stakeholders and not assumptions.

The pharmaceutical example

The moment comes that you have to create a class for medicines. What you will take under consideration for the fields (state) and the methods (behavior) of the class? Most medicines come in a variety of types or formats. The types of medicines are the following:

  • Liquid
  • Tablet
  • Capsules
  • Topical medicines
  • Suppositories
  • Drops
  • Inhalers
  • Injections
  • Implants or patches
  • Buccal or sublingual tablets or liquids

Have you been aware of that? Probably you knew some of them… but we need all of them, cause this is what the pharmaceutical company asked for! Are we done? Far from there! We still have to decide about the the methods of the class. Methods denote actions. A medicine what kind of actions does it carry? The “every X hours” frequency action is part of the Medicine class or the Prescription class? Of course is part of the Prescription class! But I believe that all of us agree, that some programmer would do that mistake. I could carry with many more examples, but I am confident that you got the point.

What if… there is no domain expert?

Well, if I were you, I wouldn’t accept the role, of let them hire me. In the past two years, I wouldn’t be able to develop software that matters with the support of the domain experts (electrical, mechanical and chemical engineers). It’s not easy to model a problem without the concrete knowledge of the domain.

Additionally, the domain expert has to have a basic IT knowledge. It is, at least unacceptable, to work with people who do not understand the basics of how a computer or a software system works. And believe me, there are a lot of them!


A piece of advice. All domains, no matter how easy or boring might seem in the beginning, they all carry knowledge and history. Understanding the domain, doesn’t just make you a better programmer, but it helps you understand how things work in a more insightful way. You become a better citizen in the end.