Types of information

The Notation Interchange File Format specification (NIFF 2002) states that music notation contains three types of information components: graphical, logi-cal, and performance. These components are loosely connected. This principle was first presented by Ornstein and Maxwell (1983; see also, Maxwell &

Orn-Music Notation as Objects

stein 1984). A similar principle forms the architectural basis of the Standard Music Description Language (SMDL). The latter groups different types of musi-cal information into domains, one of which is called visual and another gestural. The SMDL equivalent for the logical domain is called Cantus. SMDL also spec-ifies a fourth domain called analytic (Sloan 1997).

It is difficult to separate and define these components in a precise manner.

Eleanor Selfridge-Field (1997b) describes the relationships between logical,

“physical” and “practical” information by using an analogy to geographical maps. As she points out, a map may represent physical, practical, and logical information, or some combination of these. For example, one kind of map can show borders of states, and a road map represent physical presence, but both maps also constitute logical information.

In a computer program, the graphical information represents instructions for displaying visual symbols on a computer screen or on printed paper. Logical information includes invisible connections and relationships between individual graphical symbols. This includes terms such as “voices” in a polyphonic struc-ture or the durational “value” of a note. Performance information represents musical interpretation of a score. This typically includes the precise timing of notated events, phrasing, intonation, detailed use of vibrato, and so on.

The difference between performance, logical, and graphical information can be demonstrated with an example. “Quarter note middle C” can be regarded as logical expression describing musical information. The expression “one second long, 261.62 Hertz tone” can be regarded as a performance-oriented or physical expression. A corresponding graphical expression might in turn be as shown in Figure 2-1.

The notation example of Figure 2-1 could also be expressed verbally, as “a staff containing a treble clef and a quarter note with an upward stem on the first lower ledger line” or “five horizontal lines, one vertical line, a spiral-like shape, and a filled ellipse with a short horizontal line crossing it”. Both expressions can be

Figure 2-1: A simple expression using common music notation

regarded as graphically-oriented, but the first uses musical vocabulary, whereas the second uses general graphical vocabulary. This shows that even graphical types of information may be interpreted and expressed on different semantic lev-els.

The expression of pitch is often an indicator of the orientation of a represen-tation. If a pitch is coded by the note’s vertical position on a staff, it is an indica-tion that the representaindica-tion is (likely to be) graphically-oriented. By contrast, if a note name and octave range are used, then the representation can be considered as more logically-oriented. A combination of both ways of specifying pitch indi-cates that the representation is designed to express both types of information explicitly.

A purely logically-oriented representation primarily represents logical infor-mation explicitly, and graphical inforinfor-mation implicitly (either fully or in part). If a notation program uses a logically-oriented representation, it must typically calculate at least some of the placements of notation symbols automatically. A logically-oriented representation may, however, contain either optional or man-datory graphical parameters to aid in the calculation process. A graphically-ori-ented representation, in turn, encodes graphical information explicitly. A performance-oriented representation may also allow optional expression of logi-cal or graphilogi-cal information, although its typilogi-cal purpose is to express perfor-mance information in an explicit way.

In common music notation, graphical information is explicit. Logical infor-mation is implicit, and must be derived through analysis or interpretation of the graphical symbols. Performance information, for its part is mainly expressed implicitly and can be generated by interpreting the graphical information.

As noted above, graphical information may be further subdivided into sev-eral levels of abstraction. The “lowest” of these may be called the “physical”

level. In a printed score, this level would consist of ink and paper. In a computer software implementation, it might consist of primitive computer graphics (such as points, lines, curves, etc.) or of individual pixels on a computer display – these may be regarded as virtual equivalents of paper and ink. On a higher level, graphical information can be represented as complex symbols, such as notes, rests, key signatures, or staves. Some of these symbols can consist of physically separable parts. On an even higher level of abstraction, a whole musical work may be regarded as a single graphical symbol.

Performance information, too, may be represented on many abstract levels, including a stream of events or a sampled audio signal. When a musical score is performed, each note is given an exact beginning and duration in time as well as nuances such as vibrato, tone color, and more. In performance, graphical details

(such as stem direction) and logical information (such as tempo) either disap-pear or are translated into a combination of several notes or parameters.

Similarly, a detailed analysis of logical information in music notation can be expected to reveal different levels of abstraction. How SMDL distinguishes between logical and analytic domains is an indication of this. Also musical structure can be regarded as either graphical, logical or analytic information.

This raises an additional issue to be considered in evaluating the relationships and roles of the different information types. Roger Dannenberg discusses hierar-chy and musical structure in music representation. According to him, it is impos-sible to represent musical structure sufficiently in terms of a single hierarchy.

For example, beams and slurs form two different structural constructs, which often intersect (Dannenberg 1993: 20-21). Therefore, the encoding of musical structures as parts of relationships could result in a complex set of interweaving hierarchies.