PPI - A Portable Prolog Interface for Java

As a first step to combine the two programming paradigms – objectoriented programming and logic programming – we have introduced a generic default mapping for JAVA objects and PROLOG terms. This mapping can be used without any modification to the JAVA classes that stand behind the objects. We also can generate automatically JAVA classes from predicates in PROLOG that map to each other. Apart from the default mapping it is further possible to customise the mapping by JAVA annotations. This allows for different Prolog-Views on a given class in JAVA. The data exchange format between JAVA and PROLOG is a simple textual representation of the JAVA objects and of the terms in PROLOG. Because this textual representation already conforms PROLOG’s syntax, it can be directly used within PROLOG. In a second step we have to develop the link between JAVA and PROLOG that executes the mapping and communication. We already have presented a connector architecture for PROLOG and JAVA and an example interface that successfully uses our object term mapping with high performance. However, this interface depends heavily on a single PROLOG implementation: SWI-PROLOG. But as we have a generic mapping between JAVA objects and PROLOG terms, we also strive for an interface that also is generic and can be used independently of the PROLOG implementation. In this paper, we present the Portable Prolog Interface (PPI) for JAVA that uses the standard streams stdin, stdout and stderr to communicate with a PROLOG instance. Because these standard streams are available for all popular operating systems and are used by most of the PROLOG implementations for the user interaction, the PPI works for a broad range of PROLOG implementations. We evaluate our new generic interface PPI with different PROLOG engines and without changing the underlying JAVA or PROLOG source code of our tests.