Science of Design

I am really confused by this term. I can easily understand Scientific Design since the author analogize it to Operational Research. Design Science is also understandable when I replace Design with Physics, where we all learned a lot of laws and rules. But Science of Design?

According to what author said, the science of design is the study of design (principles, practices, and procedures). So does that means the science of design is an activity or process conducted in the scope of Design Science? In other words, the science of design is an effort and design science is a product. But I do feel I misinterpret these concepts somehow.

Could anyone share your thought and guide me through this?