From wiki.visual-prolog.com

Revision as of 10:04, 9 January 2008 by Kari Rastas (talk | contribs) (The article uses often the term I (writer) so the writers name is needed or the article has to be changed in a non personal "mode")

Written by Gildas Menier.

For the management of key->values in Visual Prolog, you may use factsDB, chainDB or some sql based solution. Each solution has benefits and drawbacks. For some reasons, I had to find another solution.

Mikio Hirabayashi has built a very nice API called 'QDBM'.


see also http://qdbm.sourceforge.net/benchmark.pdf

QDBM is well known in the Unix world, but has been ported to Win32. Practically, it is a disk-based Hashtable + Binary tree + inverted list package. QDBM offers many solutions called 'depot', 'curia', 'villa', 'odeum' and is well worth a look if you want to manage large amount of data.

In the enclosed project, you'll find a small 'depot' wrapper for Visual Prolog.

The example creates 1.000.000 (key, values) and then ask for 1.000.000 keys at random. All the key/values are stored on disk in a single file.

Using a collection of instances of the visual prolog class 'depot', you can manage a very large hashtable on disk.

I do not provide a full documentation since the real documentation can be found on the above web site. Only the port of depot is functional in this lib.

I tried to simplify the use of this lib as much as possible, and tried not to get too far away from the original API syntax:

NewDepot = depot::new("dtest"), % create a depot db
NewDepot:dbopen("create"), % open it (create mode)
NewDepot:dbput_string(Key, Value), % put a key,value
NewDepot:dbclose(), % close the file

and you can access the db as follows:

ReadDepot = depot::new("dtest"), % 
ReadDepot:dbopen("read"), % open it in read mode
Value = ReadDepot:dbget_string(Key), % tries to find the value for a key, fails if no value
ReadDepot:dbclose(), %

More predicates are provided. Please, have a look on the documentation of QDBM/depot and on the depot.pro file.

The project doesn't include a copy of qdbm (because of the allowed posting size); I encourage you to download the most up-to-date version on the site above. It is provided under the GNU Lesser GPL. Just copy the three following files into your exe directory:

  • libiconv-2.dll
  • mgwz.dll
  • qdbm.dll

you will find the package there:


Example project/download in Discussion forum: (how to) deal with large amounts of (key,value)