I'm really glad you asked this question. Initially I intended to post an enormously long response that included the journey that I went through when creating my martial arts system, but then I thought I was getting too far away from your question. I still have my response, but I think I'll save it for when someone asks for suggestions as to how to create a martial arts system. To answer your question, my system is rooted around the philosophy of "few movements pertaining to many scenarios". I've always felt that many self defense systems require too many moves to memorize. It can be challenging for students to remember a multitude of moves when under pressure.
For every rank that my system has there is one set of core moves to remember. They all fit into a pattern. Most defenses taught at that specific rank utilize that core set of moves. For example my white belts learn simultaneous block/punch, knee strike, push away, and run. They will then use that core set of moves for various punch defenses, certain grab defenses, etc. There are some defenses that won't utilize the core moves, such as ground defenses, but for the most part the defenses at that level are based around those core set of moves. I also warm up with attack defense drills where the students focus on attacks from four different angles (both right a left side) using the core set of moves. Those four different angles are meant to simulate most attacks that a person will see (including sticks and knife defenses). Even my stick fighting (Escrima) is based on a simple pattern of moves that are applicable to many scenarios. The purpose is that a student has muscle memory of what to defend with if attacked, and the ability to flow from one core technique to another if need be.