What is the basic difference between artist and composer tag used in audio file?

Question

Let me take an example to specify my question.

Below mentioned details are from a Bollywood album "Rockstar" by A. R. Rahman.

Title : Kun Faya Kun
Track : 04/14
Contributing Artist : A. R. Rahman, Javed Ali, Mohit Chauhan
Artist : Various Artists
Composer : A. R. Rahman
Lyricist : Irshad Kamil
Album : Rockstar
Year : 2011
Genre : Bollywood (Original Motion Picture Soundtrack)

I know that Javed Ali, Mohit Chauhan are singers, so it is clear to me that they have contributed their vocals along with A. R. Rahman (he also has a vocal) for the particular track, whereas for the artist field, it's "various artists" because various artist have contributed to this album. The music is composed by A. R. Rahman, hence in the composer field is A. R. Rahman.

Now let's take an example of a non-vocal track from the album "Various ?– Café Del Mar - Terrace Mix"

Title : Just Landed
Track : 01/13
Contributing Artist : Phil Mison
Artist : Various Artists
Composer : _ _ _ _
Album : Café Del Mar - Terrace Mix
Year : 2011
Genre : Electronic

The CD inlay has following details :

Written and produced by Phil Mison : Keyboards/Bass/Guitar by Phil Mison.

Here in this track as there is no vocal; then why is Phil Mison mentioned in the "contributing artist" field. He is a composer and should be in the composer field.

Clarification regarding contributing artist, artist, and composer tag used in audio files.

And at last a vocal track from the same above album with following details :

Title : History (M3 & Bachelors Of Science Remix)
Track : 07/13
Contributing Artist : Groove Armada
Artist : Various Artists
Composer : _ _ _ _
Album : Café Del Mar - Terrace Mix
Year : 2011
Genre : Electronic

The CD inlay has following details:

Produced by Groove Armada, Written by Cato/Findlay/Young/. Vocals by Will Young. Additional Production and remix by M3 & Bachelors Of Science Remix.

Same case here also, in contributing artist there should be Will Young instead of Groove Armada.

Answer 1

Artist

The main artist or band that played the song. This is mainly used for albums where the same artist or band plays all the songs. In the case of soundtracks or compilations, they use Various Artists. Especially for digital music (organized in folders), it is better to have one artist for one album.

Contributing Artist

Since the field "Artist" is already taken, they use this field for the main performing artists. It doesn't necessary mean singer (vocals), it can be used for instruments, producers etc... They will often use the main artists, the ones that did the bigger part of the job, that's why some minor contribution can be missed.