An Introduction to Aspect-Oriented Music Representation

Computer-music composition systems serve diverse purposes. Some draw on contrasting computing paradigms, including procedural, object-oriented, data-flow, functional, and logic programming. All such systems, provided they are sufficiently developed, are Turing-complete, but different paradigms can help facilitate different kinds approaches to music computing and new kinds of music manipulation.

In general-purpose programming, there is a recent development known as aspect-oriented programming (AOP) that has been claimed, along with related techniques, to offer new kinds of flexibility and ease of variation. The system presented here, AspectMusic, is the first substantial work we are aware of to adapt ideas from aspect-oriented programming and related techniques and explore how they might be applied to facilitate new approaches to musical exploration and manipulation. AspectMusic is an implemented framework that applies ideas at the root of AOP to the manipulation of musical materials and structures. To introduce AspectMusic,and more generally, aspect-oriented music representation (AOMR), we begin by reflecting on some various well-known features of current computer-music systems.

Interactive scoring systems effectively provide musical "word-processor"-style environments, enabling musical detail to be entered and edited on a note-by-note basis. Other approaches, such as JMusic and Common Music, attempt to provide a generalized music programming environment, albeit with a prescribed musical ontology, embedded within general-purpose programming languages. Computer music environments such as Pope's MODE system (Pope 1991) have evolved out of the requirement to support particular compositional needs, and therefore although multiple approaches are supported, ontological generality is not a prime concern.

In these and other ways, most music representations allow music to be represented and manipu-lated only within a prescribed range of preconceived musical ontologies. In contrast, AOMR has the distinctive aim of supporting whatever ontologies may be preferred by particular users. This is largely achieved by abstracting music constructs in terms of discrete areas of interest, or concerns, that may be composed together. In this way, AOMR attempts to support any perspective as a first-class entity; its operations, however, may crosscut or be scattered across existing organizational hierarchies.

In this article, we have focused on familiar and relatively simple examples using Western tonal music to explain AOMR as clearly as possible. For clarity, we proceed from the traditional dimensions of tonal music, and then we show how AOMR systematically supports various operations and conceptions that crosscut these dimensions.

AOMR appears to be particularly relevant for those musical idioms in which musical composition may be characterized in terms of a typically limited set of musical "raw materials" that are combined and reused in various ways, addressing different musical areas of interest within a particular piece of music. Well-known examples of such materials in Western tonal music include pitch sequences, rhythmic figures, and harmonic progressions that may appear in exact and transformed forms throughout a musical work. Similar transformational processes can occur at abstract levels in other idioms, with materials such as sequences of parameters that form the inputs to generative processes. Equally, AOMR is applicable to musical works and fragments based on structural prototypes that are formed through a finite set of combinatorial operations. AOMR appears applicable wherever explicit support for maintaining coherence across representational or functional shifts is useful to a composer.

In traditional areas such as those idioms we focus on in this article, it is generally argued that the reuse of materials such as those just mentioned is the principal method by which a composer achieves musical coherence and stability across different musical dimensions (Schoenberg 1967; Sloboda 1985; Cook 1987; Belkin 1999). Additionally, of course, composers may reuse materials inter-opus. In relevant styles, the general process of musical composition therefore typically requires that the composer merge together selected musical fragments to form new constructs. As a consequence, musical materials cannot generally be localized to any particular musical construct.

To take a simple example, non-problematic using conventional systems, a single melodic figure might be merged with a number of rhythmic variants, forming different phrases. Musical materials therefore tend to be explicitly restated and transformational processes re-applied...