4.4.1 Overview of PO Files

A PO file (Prolog object file) contains a binary representation of a set of modules, predicates, clauses and directives. They are portable between different platforms, except between 32-bit and 64-bit platforms.

PO files are created by save_files/2, save_modules/2, and save_predicates/2, which all save a selected set of code and data from the running application. They can be loaded by the predicates described in ref-lod.

PO files provide tremendous flexibility that can be used for many purposes, for example:

• precompiling Prolog libraries for fast loading;
• packaging Prolog code for distribution;
• generating precompiled databases of application data;
• selectively loading particular application databases (and rule bases);
• saving Prolog data across application runs;
• building and saving new application databases from within applications;

The facilities for saving and loading PO files are more than just a convenience when developing programs; they are also a powerful tool that can be used as part of the application itself.