noun: technical A representation of a plan or theory in the form of an outline or model. ‘a schema of scientific reasoning’
noun: Logic A syllogistic figure. ‘Despite only having three axiom schemata and a single inference rule, it is possible to prove any tautology in the simple Propositional Calculus, PC.’
noun: (in Kantian philosophy) a conception of what is common to all members of a class; a general or essential type or form.

Hughes
"All theory must be founded on one great fact—harmony; for harmony is the chief beauty of two or more sounds heard together. There may be figure, schemata, and all other niceties of succession and combination; but if no harmony, the music is not beautiful. It is dim, dull, and disagreeable." [Harmonies of Tones and Colours, Fragments from the Last Note-book, page 50]