An Introduction to Aspect-oriented Music Representa- Tion Journal Article

The composition of music in many idioms involves the exploitation of recurrent, recombinant musical fragments. Any given fragment may, as a consequence, appear in arbitrarily many structures, in its original or transformed state. Such a fragment is said to crosscut the musical structure, in the sense that the modification of such a fragment implies that revisions should be made to related structures. Aspect-Oriented Music Representation (AOMR), is an approach to music representation that draws inspiration from Aspect-Oriented Programming techniques in computer software. In overview, AOMR enables fragments of music to be encapsulated and associated with user-defined areas of compositional interest. New fragments may be generated by specifying transformational and combinatorial relationships with other fragments, by reference to their area of interest. In this way, AOMR separates structure from content, and enables crosscutting fragments to be stated once, with any subsequent revisions to a fragment being automatically propagated to all related fragments. In order to remain recombinant, each fragment must be independent of its ultimate temporal location. AOMR provides an approach to the arrangement of fragments within a temporal framework, and enables the content of fragments to be conditionally modified, based on factors such as location, context and provenance. An Introduction to Aspect Oriented Music Representation To appear in Computer Music Journal Submission Draft © 2007 Patrick Hill, Simon Holland and Robin Laney Computer Music Journal 2 of 18 Final Draft Introduction Computer music systems serve diverse purposes. To this end, 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 of approach to music computing and new kinds of music manipulation. In general purpose programming, aspect-oriented programming and related techniques are recent developments that have been claimed, broadly speaking, 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 will start 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 aim to provide generalized music programming environments, 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 while 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 manipulated 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 aims to support any perspective as a first-class entity however its operations may crosscut, or be scattered across, existing organisational hierarchies. In this paper, in order to explain AOMR as clearly as possible, we have focused on familiar and relatively simple examples using western tonal music. For clarity, we proceed from the traditional dimensions of tonal music, and show how AOMR supports various operations and conceptions that cross-cut these boundaries. AOMR appears to be particularly relevant for those musical genres in which musical composition may be characterized in terms of a, typically limited, set of musical "raw materials" which 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 which may appear in exact and transformed forms throughout a musical work. Similar transformational processes can occur at abstract levels in other genres, 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 An Introduction to Aspect Oriented Music Representation To appear in Computer Music Journal Submission Draft © 2007 Patrick Hill, Simon Holland and Robin Laney Computer Music Journal 3 of 18 Final Draft 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 genres we focus on in this paper, it is generally argued (Schoenberg 1967) (Cook 1987) (Sloboda 1985) (Belkin 1995-1999) that the reuse of materials, such as those mentioned above, is the principal method by which a composer achieves musical coherence and stability, across different musical dimensions. Additionally, of course, composers may reuse materials inter-opus. In relevant genres, 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 an extremely simple example, not 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 at each occurrence. Hierarchical structures are prominent in music, as indicated by the analytical work of theorists such as Schenker and Lerdahl and Jackendoff (Lerdahl and Jackendoff 1983). But since the hierarchies formed in different dimensions do not necessarily align, musical compositions tend to contain tangled hierarchies and polyarchies. For example, consider a simple pitch sequence P1 consisting of two parts PA and PB, and a simple rhythmic sequence R1 consisting of three parts RA, RB and RC. A single melodic figure constructed from these sequences results in a tangled hierarchic relationship in which there is not necessarily any correspondence between any of the parts of P1 and those of R1. Polyarchic relationships occur when a node is shared between hierarchies. Consider, for example, another pitch sequence P2, that also uses PB. Tangled polyarchies occur when elements from polyarchies in different dimensions are combined. These two scenarios are shown graphically in figure 1.