|
|
|
|
|
|
by burakemir
1306 days ago
|
|
|
It was a conscious choice to stick the prolog-like syntax because there are numerous teaching resources (e.g. "foundations of databases") and also academic research papers available that all discuss datalog in this syntax. Like tmptmpgo I consider datalog something different entirely and worthy of study in its own right; a small kernel (or toy) language that by itself is not sufficient for many day-to-day tasks. It is enough to cover relational algebra with recursion fixpoints. This gives us a handle on SQL queries. What we want is a well-behaved, predicable mix of programming and those relational operations. We have to end this SQL madness. IMHO, it is undeniably true that Prolog is one particular way of achieving such a mix (and standardized etc), but it is not the predictable, easy-to-use and well-behaved mix we want. We should be able to isolate syntactic fragments where it is easy to ensure safety properties, at the minimum the datalog fragment. That is why having a fragment correspond as close as possible to textbook Datalog was a design constraint for me. That said, when we talk implementation, there are of course a lot of optimizations that apply equally to Datalog and Prolog, say the magic set transformation. |
|
|
These are great goals! Thank you a lot for working on them, and for taking the time to participate here!
> We should be able to isolate syntactic fragments where it is easy to ensure safety properties, at the minimum the datalog fragment.
Again a great goal! Luckily, for every given Prolog program, it can be decided statically whether it is in the usually considered Datalog fragment. Likewise, for every given Prolog program, many things can be statically decided, for example it can be said statically, i.e., by just "looking" at the program without running it, with certainty that impure constructs do not occur in a given Prolog program and that these transformations can be applied without changing the declarative meaning of the program.
I think it is a very good idea to restrict oneself to a fragment of Prolog, especially if you need a lot of leeway to optimize programs, and to reason about them. For example, query optimization is much easier if you know that no side-effects occur in a Prolog program.
The question is whether all this needs any syntax beyond what standard Prolog already provides. Prolog is a very flexible language and supports user-defined operators. If possible, I recommend to keep to this standardized syntax, and to use a sensible fragment of it to facilitate reasoning, at least for as many programs as possible. The availability of existing teaching material and research papers you mentioned is another excellent argument in favor of this approach. It is perfectly OK to only support a proper subset of full Prolog, in fact that is exactly what Datalog does!