Very well, if you insist on ignoring the broader point in favor of the specific example, then replace `length` with `is`. We can unify `X is 3 * 3`, we cannot unify `9 is 3 * X` (at least not in SWI-Prolog v8.4.1). Therefore, we can call the thing to the left of `is` the output and the thing to the right of `is` the input.
Hi, and thanks for your comments. I'm Torbjörn - the guy behind the book manuscript and the proof-of-concept implementation.
Well, the book manuscript still needs a chapter dealing with possible use cases - I'm thinking of web-based conversational agents (using an actors as dialogue managers, DCG for grammars and and speech recognition and -synthesis built into browsers). Or a game of some kind perhaps - with game AI using Prolog.
Also, I like to think of the Prolog Web as a killer app. The idea of "wrapping the regular web in logic" appeals to me. Not as a replacement for the semantic web, but as something running alongside it, making it more easily programmable. And the Prolog Web comes with an architecture, something which is not true of the semantic web AFAIK. Of course, the Prolog Web also lacks a lot of features promised by the semantic web - a logic sufficiently expressive to built ontologies for example. The Prolog Web tries to complement the Semantic Web, not to replace it.
You are right that for some applications, only what is offered by the ISOBASE or ISOTOPE profiles will be needed. But something like the IDE in the PoC cannot be be served by those profiles - the ACTOR profile is needed there. Or consider a multiplayer game that requires the server to send periodic snapshots of the world state to the client. This is better handled using push technology, rather than pull, and server push is only offered by an ACTOR node.
I agree that a SaaS company might offer an API to a Prolog in the cloud. (I should talk to the people behind SICStus Prolog about that - one of the few commerical Prolog vendors still in existence. :) And no, that's not an "open Web". But what is usually referred to as the open web is only open by default
isn't it, until someone choose to "close" it and charge for access. Hopefully, enough people in the Prolog community would choose to keep the Prolog Web open.
?- length(X, 3).
X = [_1586, _1592, _1598].
?-