Also I did not know the term "fluent interface" before, we realized, that we already used this in the eZ components, to be more exact, in our Database package, which gives you a quite good ammount of SQL abstraction.
The new buzz term "fluent interface" has been mentioned a lot in the PHP world recently, so I will not again explain, what a "fluent interface" is. Andi already mentioned, that this way of desining an API is quite good and can give you a really handy interface, but he also points out, that one should make very careful use of the technique.
He gives a brief example from their code, and explains how it works. The statement selects from a table "Person" where the age is greater than 15 and orders it by the "full_name" field, limit of 10 rows returned. With the "fluent interface" concept, that's pretty much how the statement "reads" as well...
