Functional and relational are 2 sides of the same coin. For instance: x + y = z Can be viewed as either a function called binary_addition with x & y as inputs

Functional and relational are 2 sides of the same coin. For instance: x + y = z Can be viewed as either a function called binary_addition with x & y as inputs and z as the output, or as the description of a relationship between 3 sets. So, to solve the problem using SQL for example you would create a table binary_addition(x,y,z) and then fill it with all the true values that caused x + y = z to be true and then say "select z from binary_addition where x = 4 and y = 4" In the functional model the computer stores the process for turning the input values you give it into the output values you want. In the relational model the computer stores a table containing all known possible input values, all known possible output values, and how they relate to each other, and gives you a way to retrieve them. Note, the functional model is implemented by what that famous guy whose name I can't remember called "function-level" programming languages, not functional (aka lambda) languages.