Preferahbly as many as you can. Then you’ve got a really useful service that people can build into their applications.

Here’s one to look forward to: The BBC’s programme catalogue.

It turns out there’s a huge database that’s been carefully tended by a gang of crack BBC librarians for decades. Nearly a million programmes are catalogued, with descriptions, contributor details and annotations drawn from a wonderfully detailed controlled vocabulary.

7 million rows of data going back to the 1930s. Wow.