This has always bothered me: What really is meant by "business logic"?
Wikipedia defines it as "In computer software, business logic or domain logic is the part of the program that encodes the real-world business rules that determine how data can be created, displayed, stored, and changed."
Seems to me that 3/4 of that is the definition of the relational model.
Created: Defining the reality that is being modeled by the systems, using relational tables and attributes, defining the property rules and class rules (column constraints and table constraints like FKs).
Stored: Physical layer of the database defines the process of implementing the logical model, adding indexes, computed columns, partitions, filegroups, etc etc.
Changed: Much of what defines how data can change is defined in the class rules of the logical model. Certainly complex calculation and input is handled by an application interfacing with the database, but these changes must be approved by the database, which is *model* of reality.
Displayed: The one place where the database doesn't have much say. It's the job to the person or tool querying the database to decide how best to display the resulting set that the database provides.
The answer has always been in understanding that a computer database system provides a *model* of a reality outside of the computer. A person buys a product and interacts with a sales representative. A couple gets married on a date in a county. A person writes a message to be shared with their friends. We live in a real world that is *modeled* by a computer system. Too often we lose sight of this and we enagage in reification, turning the computer system into the reality - the data that's in the system *becomes* reality.
Modifying a well modeled database (5th NF +) is easy to do since all the rules are defined there. Instead when rules and processes are scattered throughout the inputs of any model, change is *more difficult*, not less. Of course, this assumes a well modeled database, which most businesses have been running from for ages, because it requires *knowledge* of what the business actually does!