we collected information about several kind of resources
which deal with symbolic notated music (sheets), descriptive metadata (e.g. artists, genres, cataloguing information), and audio files
we mainly relied on resources realized by researchers and targeted to researchers, but we also found other target audiences
the majority of resources offer digitizations of scores and lyrics, followed by audio files and structured data, which are published in several formats
the scale of aggregators of resources (such as catalogues, digital libraries, datasets, repositories, and digital editions) may vary significantly
aggregators gather items by genre, artist, period or country
generally providers offer different kinds of information related to the musical resources they publish, from general descriptive metadata to more specific data on melody, harmony, rythm etc.
in order to reuse such resources, several open licenses are available - even if most of the providers do not specify it clearly