Overview

Prolog Logicbases

Prolog is a unique language in that it more closely resembles a database than a procedural programming language. In fact, the theoretical roots of Prolog are the same as those for relational database. For this reason, a Prolog program is more accurately referred to as a logicbase, that can be queried much the same way as a database.

The Amzi! Logic Server takes advantage of this characteristic to present Prolog logicbases to other programming languages and environments in much the same way databases are presented. This approach lets the host language interface with Prolog in a manner that is very natural for both the host language and Prolog.

The result is application programs can easily take advantage of Prolog's logical rules, pattern-matching and automatic search capabilities for adding services such as natural language processing, formal language processing, expert advisors, intelligent agents, smart help, or just plain application logic concisely coded in Prolog.

Architecture

At the core of Amzi! is a runtime engine that can load and run compiled (static) and/or interpreted (dynamic) Prolog code.

The developer writes, tests, debugs and compiles Prolog programs/logic-bases using either the Interactive Development Environment (IDE) or command line tools.

Compiled Prolog is stored in binary files (.xpl Files) which can be loaded by the Prolog engine. Compile Prolog code can also be loaded from .plm files (after the .xpl file is loaded). Interpreted code is stored in text files and can be read (consulted) by any Prolog program.

Logic Server Engine and LSAPI

The Logic Server is simply the Prolog runtime engine packaged as a dynamic library (.dll or .so) that can be linked with other applications. The Prolog engine is two classess: one for the engine and one for exception handling. These objects have a number of public methods, which correspond to the functions of the Logic Server API (LSAPI).

Multiple engines are implemented simply by allocating a new Logic Server/Engine object. This can be done through either the native LSAPI interface, the C++ Logic Server class, or any of the environment specific lsapis, Delphi, VB, or Java. The application program interface (LSAPI) is the collection of methods exported by the Logic Server.

The LSAPI includes a wide range of functions that let the host program load Prolog logic-bases and access them with the full range of capabilities a Prolog programmer has using a Prolog listener, including the ability to backtrack through multiple solutions to a query and assert and retract dynamic clauses. The LSAPI also makes it easy to map Prolog terms, structures, lists, and variables to the corresponding structures in the host language.

Extending Prolog

While the logical aspects of Prolog are what make it a powerful tool, it is the built-in predicates that provide functions that make Prolog a practical language. These built-in predicates provide extra-logical capabilities such as reading and writing from files.

The Logic Server provides an interface for implementing custom built-in predicates, called extended predicates. Extended predicates make it possible for Prolog to directly access any services available to the host language, such as graphics, database, numerical analysis, or any other specialized functions.

Extended predicates can only be implemented in languages that support function pointers, such as C/C++, Java, Delphi Visual Basic 6 or later.

Extended predicates can be implemented for specific applications, or packaged in dynamic/shared libraries, called LSXs (Logic Server eXtensions), that can be shared by different applications.

Supported Environments

Because the Logic Server is written in C++, it is extremely portable and can support a number of environments. Under Windows, support is provided for both regular and console applications.

Because the Logic Server is written in C++, the core API is defined both as C functions and as C++ classes. These can be readily accessed by any environment that can call a dynamic library.

Some environments are further served by language-specific classes, such as Java, Delphi and .NET. In these cases the Logic Server includes an additional component providing a mapping from the host language to the Logic Server dynamic/shared library.