MusicDiff: A Diff Tool for MEI

For musicologists, the collation of multiple sources of the same work is a frequent task. By comparing different witnesses, they seek to identify variation, describe dependencies, and ultimately understand the genesis and transmission of (musical) works. Obviously, the need for such comparison is independent from the medium in which a musical work is manifested. In computing, comparing files for difference is a common task, and the well-known Unix utility diff is almost 46 years old. However, diff, like many other such tools, operates on plain text. While many music encoding formats based on plain text exist, formats used in the field of Digital Humanities are typically based on XML. There are dedicated algorithms for comparing XML as well,1 but they only focus on the syntax of XML, but not the semantic structures modelled into such standards as MEI. MEI seeks to describe musical structures, and the XML syntax is just a means to express those structures. A diff tool for music should focus on comparing musical structures, but not the specifics of their serialization into a file format. In Beethovens Werkstatt, a 16-year project focussed on exploring the concepts and requirements of digital genetic editions of music, based on and arguing with examples from Ludwig van Beethoven, a case-bound diff tool for music was developed. The following paper discusses how that specific tool can be generalized, and which use cases such a tool may support