This presentation will focus on the maintainability quality attribute — how to keep business logic isolated, consolidated, encapsulated, and consistent, as well as how to integrate it with the infrastructure layer, including persistence, messaging etc. We will explore the practical application of the following approaches: - OOD / Rich Domain Model / DDD - Hexagonal layered architecture - CQRS / Persistence / ORM All these aspects will be illustrated through a real-world task example and its implementation approach (code examples will be in .NET).