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> That's actually one case where Datalog works better than SQL, that only allows "rows" i.e. "facts" (in Datalog parlance) but not "rules" that establish relati

by juki 5y ago

> That's actually one case where Datalog works better than SQL, that only allows "rows" i.e. "facts" (in Datalog parlance) but not "rules" that establish relations _between tables_. What is the difference between Datalog rules and SQL views?

YeGoblynQueenne 5y ago
It's been a while since I used SQL and I'm a bit rusty in it, but views would probably be the equivalent of Datalog rules, yes. The difference, as in my other comment to OP, is that Datalog rules are part of the Datalog program, which also stores the actual "tables" i.e. the facts. Whreas in SQL, views are only sort of ... virtual? Like I say I'm a bit rusty- but from my understanding, SQL vies don't live in the same space as tables. Funny thing. It used to be my day to day work was 80% SQL. Nowadays it's 99% Prolog maybe with a little bit of bash and powershell scripting (gotta automate those experiments!). I kiiind of miss SQL? But not quite. Personally I don't 100% get the grumbling about SQL's syntax. It's unintuitive and it works very hard to hide the actual semantics behind it, but, eh, at least it has clean semantics. I recently found this free book on databases that goes over both SQL and Datalog. It's a bit thick with obtuse terminology but it actually goes in depth over many useful topics: http://webdam.inria.fr/Alice/ http://webdam.inria.fr/Alice/ I also recommend that to OP, if they're reading.
- christmm 5y ago
  mind informing what you use Prolog for, and strengths?
  - deleted 5y ago
    [deleted]
  - YeGoblynQueenne 5y ago
    I use Prolog for my research. I study Inductive Logic Programming (ILP) for my PhD. ILP is a field in the intersection of machine learning and logic programming, that studies approaches to learning logic programs from examples, background knowledge and language bias (it helps to think of background knowledge as a library of sub-routines from which a program is to be composed and to think of language bias as constraints on the structure of learned programs). Obviously Prolog is well-suited for this task, but there's a reason why you don't often hear of "Inductive Python Programming" or "Inductive Java Programming", say. The reason is that imperative languages tend to have lots of specialised syntax, for example for class declarations, loops, variable assignment etc. Whereas Prolog syntax consists entirely of one kind of expression, the Horn clause. So for instance, to learn a program with a "loop" in Prolog you "only" need to add a recursive clause to the program, where a recursive clause is simply an ordinary Horn clause with the same predicate symbol in a head literal and one or more body literals. To learn a program with a loop in Python you have to add the loop to the program as a specialised structure with its own peculiar syntax. Also, because in Prolog everything is a Horn clause, examples, background knowledge and language bias can be (and often are) represented as Prolog programs themselves, so it's possible to learn new background knowledge, new language bias and even new examples. That'd be tricky to do in Python where examples, say, would be not programs, but the inputs of and outputs to programs. The sister field to ILP, of Inductive Functional Programming exploits the homoiconicity of functional languages in similar ways. Finally, Prolog is a language with a deductive inference algorithm as an interpreter and it turns out deduction can be sort of inverted into induction. Which is to say, we can go from reasoning to learning, with but a tiny little hop. Well, ish. If you're interested in more details about my work, there's links in my profile.

by juki 5y ago

YeGoblynQueenne 5y ago

It's been a while since I used SQL and I'm a bit rusty in it, but views would probably be the equivalent of Datalog rules, yes. The difference, as in my other comment to OP, is that Datalog rules are part of the Datalog program, which also stores the actual "tables" i.e. the facts. Whreas in SQL, views are only sort of ... virtual? Like I say I'm a bit rusty- but from my understanding, SQL vies don't live in the same space as tables. Funny thing. It used to be my day to day work was 80% SQL. Nowadays it's 99% Prolog maybe with a little bit of bash and powershell scripting (gotta automate those experiments!). I kiiind of miss SQL? But not quite. Personally I don't 100% get the grumbling about SQL's syntax. It's unintuitive and it works very hard to hide the actual semantics behind it, but, eh, at least it has clean semantics. I recently found this free book on databases that goes over both SQL and Datalog. It's a bit thick with obtuse terminology but it actually goes in depth over many useful topics: http://webdam.inria.fr/Alice/ http://webdam.inria.fr/Alice/ I also recommend that to OP, if they're reading.

christmm 5y ago
mind informing what you use Prolog for, and strengths?
- deleted 5y ago
  [deleted]
- YeGoblynQueenne 5y ago
  I use Prolog for my research. I study Inductive Logic Programming (ILP) for my PhD. ILP is a field in the intersection of machine learning and logic programming, that studies approaches to learning logic programs from examples, background knowledge and language bias (it helps to think of background knowledge as a library of sub-routines from which a program is to be composed and to think of language bias as constraints on the structure of learned programs). Obviously Prolog is well-suited for this task, but there's a reason why you don't often hear of "Inductive Python Programming" or "Inductive Java Programming", say. The reason is that imperative languages tend to have lots of specialised syntax, for example for class declarations, loops, variable assignment etc. Whereas Prolog syntax consists entirely of one kind of expression, the Horn clause. So for instance, to learn a program with a "loop" in Prolog you "only" need to add a recursive clause to the program, where a recursive clause is simply an ordinary Horn clause with the same predicate symbol in a head literal and one or more body literals. To learn a program with a loop in Python you have to add the loop to the program as a specialised structure with its own peculiar syntax. Also, because in Prolog everything is a Horn clause, examples, background knowledge and language bias can be (and often are) represented as Prolog programs themselves, so it's possible to learn new background knowledge, new language bias and even new examples. That'd be tricky to do in Python where examples, say, would be not programs, but the inputs of and outputs to programs. The sister field to ILP, of Inductive Functional Programming exploits the homoiconicity of functional languages in similar ways. Finally, Prolog is a language with a deductive inference algorithm as an interpreter and it turns out deduction can be sort of inverted into induction. Which is to say, we can go from reasoning to learning, with but a tiny little hop. Well, ish. If you're interested in more details about my work, there's links in my profile.