Ars Technica reports that "social networking giant Facebook has acquired FriendFeed. This deal reflects Facebook's growing fixation on the social stream, but it's hard to see how the two services will be merged. [...]
[Facebook's] powerful but esoteric SQL-like query system all add up to a steep learning curve. By comparison, FriendFeed has a simple and elegant API that exposes a lot of information and is much more accommodating to developers."
It seems to me that streaming SQL is the correct solution to this problem. Not a SQL-like language, not an API (although you of course have to use an API to execute queries and get the results), and not just traditional SQL on finite relations, but SQL where streams are a first-class construct.
I'm not a big believer in 'SQL-like' languages; they give SQL a bad name. Someone once said that the C programming language combines all the power of assembly language with all the ease-of-use of assembly language. The same could be said for 'SQL-like' languages: they tend offer limited capabilities of a fixed API, but you have to learn a new language to do so.
Full SQL is difficult to implement because it must be possible to combine the relational operators (join, filter, union, project, and so forth), and other language features such as types and built-in operators, in any combination. Implementors often give up on this (what language designers call orthogonality), and what they get to is termed a SQL-like language. The full power of SQL only accrues when the implementor has implemented the whole language, and achieved orthogonality.
Nor can the problem be solved particularly easily or efficiently using regular SQL, because every query is going to be of the form 'tell me what has changed since I last ran the query'. That kind of activity throws a conventional database into a tailspin.
So, streaming SQL could solve this problem. Has anyone tried it?