Engineering standards & science
It is common to define engineering as applied science. A more accurate idea is to recognize that science is about ideas and theories. Engineering uses science to build or create things: computer programs, bridges, machines, etc. Any kind of artifact.
Aside from science are what I call established practice. This is where you find engineering standards. You find these in building codes, manufacturer specifications, etc. Various trade associations publish what are defacto accepted engineering practices: the Southern Pine Association, the American Institute of Timber Construction, the American Institue American Institute of Steel Construction. and the American Concrete Institute.
Engineering standards regarding slab-on-ground foundations address how they are to be designed and constructed. What they do not address is how they are expected to perform.