CODEWITHSUNDEEP
databasepostgresqlprolog
iffs
iffs

Reputation: 73

Is there a way to translate database table rows into Prolog facts?

After doing some research, I was amazed with the power of Prolog to express queries in a very simple way, almost like telling the machine verbally what to do. This happened because I've become really bored with Propel and PHP at work.

So, I've been wondering if there is a way to translate database table rows (Postgres, for example) into Prolog facts. That way, I could stop using so many boring joins and using ORM, and instead write something like this to get what I want:

mantenedora_ies(ID_MANTENEDORA, ID_IES) :- 
  papel_pessoa(ID_PAPEL_MANTENEDORA, ID_MANTENEDORA, 1),
  papel_pessoa(ID_PAPEL_IES, ID_IES, 6),
  relacionamento_pessoa(_, ID_PAPEL_IES, ID_PAPEL_MANTENEDORA, 3).

To see why I've become bored, look at this post. The code there would be replaced for these simple lines ahead, much easier to read and understand. I'm just curious about that, since it will be impossible to replace things around here.

It would also be cool if something like that was possible to be done in PHP. Does anyone know something like that?

Upvotes: 4

Views: 2429

Answers (3)

CapelliC
CapelliC

Reputation: 60024

There is the Draxler Prolog to SQL compiler, that translates some pattern (like the conjunction you wrote) into the more verbose SQL joins. You can find in the related post (prolog to SQL converter) more info.

But beware that Prolog has its weakness too, especially regarding aggregates. Without a library, getting sums, counts and the like is not very easy. And such libraries aren't so common, and easy to use.

I think you could try to specialize the PHP DB interface for equijoins, using the builtin features that allows to shorten the query text (when this results in more readable code). Working in SWI-Prolog / ODBC, where (like in PHP) you need to compose SQL, I effettively found myself working that way, to handle something very similar to what you have shown in the other post.

Another approach I found useful: I wrote a parser for the subset of SQL used by MySQL backup interface (PHPMyAdmin, really). So routinely I dump locally my CMS' DB, load it memory, apply whathever duty task I need, computing and writing (or applying) the insert/update/delete statements, then upload these. This can be done due to the limited size of the DB, that fits in memory. I've developed and now I'm mantaining this small e-commerce with this naive approach.

Writing Prolog from PHP should be not too much difficult: I'd try to modify an existing interface, like the awesome Adminer, that already offers a choice among basic serialization formats.

Upvotes: 1

DaveEdelstein
DaveEdelstein

Reputation: 1256

I can think of a few approaches to this -

  1. On initialization, call a method that performs a selects all data from a table and asserts it into the db. Do this for each db. You will need to declare the shape of each row as :- dynamic ies_row/4 etc

  2. You could modify load_files by overriding user:prolog_load_files. From this activity you could so something similar to #1. This has the benefit of looking like a load_files call. http://www.swi-prolog.org/pldoc/man?predicate=prolog_load_file%2F2 ... This documentation mentions library(http_load), but I cannot find this anywhere (I was interested in this recently)!

Upvotes: 1

thanos
thanos

Reputation: 5858

check the ODBC interface of swi-prolog (maybe there is something equivalent for other prolog implementations too)

http://www.swi-prolog.org/pldoc/doc_for?object=section%280,%270%27,swi%28%27/doc/packages/odbc.html%27%29%29

Upvotes: 1

Related Questions