There seems to be some confusion about whether specializations of musical artists are themselves subtypes or professions. For example, there are hardly any instances of "singer" in freebase (only 5?), despite their being many musicians for whom it is clear that they are singers. Sometimes musicians have associated profession of "singer". But there is no type for "singer", so I don't see any way to easily add that information.
Why is "songwriter" a type, but "singer" only a profession?
Discussions on Musical Artist Documentation
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The main reason for the Songwriter type is to enable the properties for songs composed and lyrics written. Singers of recorded songs are generally reflected by either band membership, direct recording credit, or contributions, so a separate type isn’t needed. The profession probably is a more appropriate place to record that information unless and until someone comes up with a compelling case for a Singer type.
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I think the use you point out is fine. I have two basic use cases in mind:
1. Find all the singers in Freebase. Unless you know in advance that the way you find this is via profession attributes on musical artist types, you will not be able to do this. Instead you will find the 5 instances of singers as types that someone has created. This is confusing.
2. Extract out from Freebase properties with which to tag individuals. In the case of musical artist or other types, this is easy (you just use the type). In the case of singers, you have to have separate logic that checks the profession slot to determine that the person is a singer.
If we're going to be using key information sometimes in a profession attribute, and sometimes in a type, one thing that would help would be an explicit handle on the possible (or existing) values for an attribute on that type, with a way to find all the instances that have that value. Then it would be clear when looking at a musician that there are multiple kinds (almost subtypes...) based on the profession.
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