PostgreSQL-Prolog: A Prolog library to connect to PostgreSQL databases

https://github.com/aarroyoc/postgresql-prolog

by triska • 5 years ago

99 20 5 years ago

hirundo• 5 years ago

The Datalog query language is a subset of Prolog. I wonder how hard it would be to translate Datalog into SQL and query PostgreSQL with that. XTDB (aka Crux), which uses Datalog, supports some limited SQL querying. How limited would it be to go in the other direction?

dgb23• 5 years ago

If you’re ok with typecasting then it’s relatively straight forward. I think postgres has some convenient utility around that.

maweki3• 5 years ago

With recursive common table expressions it is really straightforward. You just have to manually stratify your datalog program to find out the order for the CTE.

And then you just write down all the rules.

edit: As long as queries aren't recursive in a difficult manner, like co-recursive or have multiple recursive calls in the same rule.

koeng• 5 years ago

This is extremely cool and I will be testing it out. I’m building large systems for handling biological data, and have wanted to use prolog for that use, but couldn’t fit all of my data in RAM. This could help me a bunch.

triska3• 5 years ago

Importantly for this use case, Scryer Prolog represents lists of characters very compactly internally, using a sequence of raw bytes! It is the first Prolog system to use this efficient representation. This helps considerably when processing huge amounts of data, for example when parsing large text corpora with Prolog's built-in grammar mechanism, definite clause grammars (DCGs).

tannhaeuser2• 5 years ago

Sure about that? It is/was pretty common to keep strings as long as possible, and convert to list of chars lazily only when absolutely necessary.

still_grokking• 5 years ago

A little bit off-topic, but still related: I could imagine the Flix language being a good fit for that use case.

https://flix.dev/

It has first-class Datalog constraints as a language feature!

As being a FP language it's of course good at modeling data. At the same time it's fast enough for heavy tasks: It runs on the JVM, having also access to its rich ecosystem.

infogulch• 5 years ago

Wow pretty cool. The next thing it needs is query params so you can avoid sql injection / unreliable user-maintained escaping rules.

EamonnMR• 5 years ago

Very cool. I really think that prolog's future hinges on its interop with sql.

TedDoesntTalk• 5 years ago

Last I used prolog was about 1990 (more than 30 years ago). I’m glad to see it still evolves!

void_mint• 5 years ago

I love Prolog and I love Postgres.

maweki3• 5 years ago

Prolog and side-effects are a really unfortunate pairing. What I would love is when backtracking over a side-effect, that effect would be taken back. With transactions that might even be possible.

As it stands, quering (pseudocode) "connect(C), insert(C, data), false" has no solution but side-effects.

SLD-resolution probably just does not work with side-effects.

Twisol2• 5 years ago

In some sense, whenever there's a choice (or a checkpoint) between two branches, each branch should morally get its own copy of the world; and effects should only leak out when both branches incur the same observable effect. (This is motivated by the logical law `(A v B) ^ (A -> C) ^ (B -> C) -> C`.)

Of course, that's hard to do when interacting with external systems!

maweki3• 5 years ago

Do you know of any work on this? I have a prototype implementation for a side-effects prolog library with a similar semantics and I'm working on the corresponding paper.

dreamcompiler• 5 years ago

This appears to merely be a Prolog wrapper around SQL queries which still have to be written explicitly. Prolog itself is a dramatically more expressive query language than SQL; using Prolog instead of SQL would be a big win (IMHO) but this library doesn't appear to do that.

fraber• 5 years ago

The following post is from October 2020, but I remember having used an interface to PostgreSQL more than 10 years ago: https://swi-prolog.discourse.group/t/swi-prolog-connecting-t... For those who don't get it: side-effects allow for the power of Prolog, just don't use them if you don't want them...

PostgreSQL-Prolog: A Prolog library to connect to PostgreSQL databases

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