I have already written about all the common roles in a product team, but in some companies, there is another role that exists and it goes by various titles including Subject Matter Experts (SME) or Domain Experts.
The defining characteristics of these people is that they are experts in the particulars of what the business does. For example, it’s normal for tax software companies to have tax experts on staff, and for payroll services companies to have a few people that have deep knowledge of the national, state and local regulations regarding compensation and payroll taxes, and health care software companies to have physicians, nurses or other medical specialists.
In general, knowledge of the application domain is squarely in the responsibilities of the product manager, but for some products, there is so much specialized knowledge that it absolutely makes sense to provide the organization (especially the product managers) with direct access to true domain experts.
The product manager will utilize these subject matter experts in several cases. During product discovery, they will use these people to gain deeper insight into the market, the users, the domain and especially the necessary business logic. Similarly they will be very useful to the QA organization as they work to define test cases and understand expected behavior, and help with acceptance testing.
You will need to use care not to consider these subject matter experts as a substitute for talking directly to customers and users. In general, your subject matter experts will not be representative of your customer base. If your customers actually had direct access to people like your subject matter experts, they probably wouldn’t need your software. Your experts will know much more about the domain than a typical customer, and of course they will care much more about your company than any customer would.
Organizationally, companies often don’t really know where to put the subject matter experts. Sometimes they are part of the QA team, and sometimes part of the product management team, and other times you find them just hanging off to the side of the org chart. I prefer to see them closely associated with the product management team because primarily they are a shared resource to the product managers, and the product managers need to be encouraged to use them early and often in their product discovery work.
This is not a role that most companies need in that it is usually reasonable to expect the product managers to become expert in the domain, and to play this role for the product. But for certain products where the domain expertise required is extensive, this role can be a valuable, highly leveraged resource for the company.