What’s on television tonight? What was on the radio last week? For some people, these are more than just casual questions.

Advertisers, for instance, want to know exactly how often and on what media their adverts are being flighted. They also want to know what competitors are doing. Copyright owners want to know what songs are being played on radio stations – and how often – so that royalties due can be calculated accurately. Analysts would like to know how many negative mentions of a political party there were on television last month.