I sometimes hear wonderful music somewhere (TV, mobile phone ring, radio...) and wonder what is the title of the music. This is especially useful when it is hard to hear the lyrics or only the melody suddenly pops out of my mind, and most classical music does not have lyrics. Without words, the only input into such search would be the sound. However, it is hard to ask a computer to match the sound recorded from my singing to a music database, nor is it feasible to search through the database by listening.
After some thinking, I come up with a method to do this: searching the sol-fa names of part of the music in a database containing sol-fa names of many songs. Say inputting 'd r m d m d m' will give a search result containing the song "The Sound of Music". And then, the sheet music can be found for playing on the piano. A Google search does not suggest anybody is doing that yet, so this may be a business opportunity.