Traditional harmonic analysis annotations can be represented in a computer model of a piece of music by plain text strings. But whenever automated processing like analysis, comparison or retrieval is intended, a formal definition is helpful. This should cover not only the syntactic structure, but also the semantics, i.e. the intended meaning, and thus adheres to the technique of mathematical remodelling of existing cultural phenomena. The resulting models can serve as a basis for automated processing, but also help to clarify the communication and discussion among humans substantially. This article proposes such a definition in four layers, which address different problems of encoding and communication: (a) relation of symbol sequences to staff positions, (b) combining functions, (c) chord roots, and (d) interval structure and voice leading. Only one of them is specific to functional (Riemannian) theory and can possibly be replaced to represent scale degree theory. The proposal is configurable to different interval specification methods and open to localisation. Syntax and semantics are defined by precise mathematical means, borrowed from computer science, and thus are unambiguously documented.

The different labelling systems defined by the functional theories of harmony have been developed from about 1870 to 1950, without the help of computers. The complexity of harmonic labels spans from pure triads over added characteristic dissonances, over alterations of the fifth, up to non-chord notes like suspensions. Computer-based evaluation of functional label expressions shows that thereby their cardinality increases up to several thousands. For this, we present the basic theory, a concrete program implemented in Prolog, and some empirical results. The software is capable of analysing historic published analyses by inductively collecting all appearing labels, as well as theories as such, where the set of labels is given deductively, by regular expressions. A major application is the mining for possible modulation chords, i.e. different functional labels which result in (enharmonically) the same pitch classes. That this strategy had actually been applied by composers manually is explained by significant examples from the Romantic period.