Clips
The following form is the beginning of a DJ-based music tagging system. Musical clips (e.g. songs, loops, random sounds) are given custom values like key, tempo, and my own semantic tags. Those values are inserted into a database when the form is submitted.
When I'm playing a particular clip during a DJ set, I instruct the database to return clips that are friendly to the clip that is currently playing.
By friendly, I mean that they share certain attributes that would contribute to a good mix (similar tempo/key), but that they also may assist in taking the mix in a different direction.