Bags of words, edit distance (as see in bioinformatics, hamming distances, cunning kernels and vector
spaces over documents. Vector spaces induced by document structures.
Metrics based on generation by finite state machines,
Maybe co-occurrence metrics would also be useful as musical metrics?
Blei, David M., Andrew Y. Ng, and Michael I. Jordan. 2003. “Latent Dirichlet Allocation.” Journal of Machine Learning Research
3 (Jan): 993–1022. http://www.jmlr.org/papers/v3/blei03a.html
Selinger, Peter. 2009. “A Survey of Graphical Languages for Monoidal Categories.”
In A Survey of Graphical Languages for Monoidal Categories
, 813:289–355. Lecture Notes in Physics. Springer Berlin / Heidelberg. http://arxiv.org/abs/0908.3347