This document summarizes Daniel Moody's research on establishing scientific principles for constructing effective visual notations in software engineering. It discusses Moody's descriptive theory that explains how visual notations communicate through encoding and decoding processes. It also outlines Moody's prescriptive theory, which proposes seven principles for designing visual notations, including principles of semiotic clarity, perceptual discriminability, semantic transparency, and complexity management. The principles are intended to guide the development of visual notations that clearly and efficiently convey semantic meaning.