What is the physical interpretation of Normal, Roughness, Albedo and Metalness map?
Those parameters have no direct physical equivalent. They were chosen to be intuitive and to range from 0-1. See the Burley's Physically-Based Shading at Disney for the full rationale and derivation of what is now commonly referred to as "PBR".

The "metalness" parameter is a simple blend between two models - one dielectric BSDF with a coloured diffuse and white specular, and a metallic BSDF without diffuse and a coloured specular component.