Omphalos Context-Free Language Learning Competition FAQ

So what's Omphalos all about?
Omphalos is a language induction competition in the same lines as Abbadingo and Gowachin, both of which concentrated on regular languages. Omphalos concentrates on Context-Free Languages.
What does Omphalos mean?
The Omphalos stone was the location of the main sanctum of the shrine of the Delphi Oracle. In ancient Greek "Omphalos" means "the centre of the earth" (from ).
Do I need to register in order to participate in the competition? Are there any fees?
No and no. Participants may optionally register for the competition by sending e-mail to . We will put registered participants on a mailing list for competition-related announcements.
How many times may I consult the Oracle?
The same requirements as the Abbadingo competitions apply:
Participants should tune their algorithms in their own time and then submit one test set labelling per problem per algorithm. Participants are allowed to rethink their approach and try again, but they are not allowed to flood our system with guesses.
To be specific, anyone who deliberately consults the Oracle more than 25 times in one day will be disqualified, as will anyone who mounts any kind of security or denial of services attack against the Omphalos server.
But what if I have a really really good reason to submit lots and lots of queries to the Oracle, would it be okay then?
In response thus spake the Oracle:
Foolish mortal! Accost not the font of truth with your idle speculations! The answer would still be no. Nobody is allowed to annoy the Oracle for any reason. The Oracle needs her rest.
Figuring out how to generate the best possible hypothesis from the available training data is part of the competition. You might want to think about cross-validation.
What kind of language was I supposed to learn again?
The ultimate goal we're pursuing is to learn any context-free grammar. The first four problems are deterministic; the last two problems are non-deterministic context-free languages. You can find more info on the data sets page.
What output do I get from the Oracle?
The Oracle returns either PASS or FAIL. The Oracle will only give a PASS when all answers to the test set are correct.
What should I do when the Oracle give me a PASS?
A valid solution is accepted when the Omphalos administrators have checked it. This means that once you get a PASS, you should contact them using the email address. The administrators will check the solution by hand and once they have approved, credit will be given. Note that even though the results are checked by hand, the Oracle needs to approve first (by returning a PASS).
What do I do if my question is not on this list?
Send an email with the question to:

Omphalos is being organized and administered by:

Brad Starkie , François Coste and Menno van Zaanen

You can contact them for comments and complaints at

Valid CSS! Valid HTML 4.01!