7 Interfacing .NET and Java

SICStus Prolog supports two different ways of interfacing a Prolog program with a Java client, and one for interfacing with a .NET client.

SICStus Prolog provides a uniform way of interfacing to Java and .NET clients via the PrologBeans (see lib-prologbeans) interface. This is a loosely coupled interface, which means that the client code runs in a different process from the Prolog code. In fact, the client program and the Prolog program can run on separate machines, since the communication is done via TCP/IP sockets. This design has the following advantages over a tightly coupled interface, where they run in the same process:

• There is no competition for memory or other process-wide resources between the virtual machines of the client (.NET or JVM) and of Prolog.
• Distribution over a network is trivial when using PrologBeans. The application is distributable from the beginning.
• PrologBeans has support for user session handling both at the Java level (with support for HTTP sessions and JNDI lookup) and at the Prolog level. This makes it easy to integrate Prolog applications into applications based on Java servers.

The main limitation of the design is that callbacks from Prolog to the client is not provided for.

PrologBeans is the recommended package unless you have special needs and are interfacing with Java in which case you may consider using Jasper.

For interfacing to Java clients SICStus Prolog also provides Jasper (see lib-jasper), a “tightly coupled” interface. This means that everything runs in the same process (the necessary code is loaded at run time via dynamic linking).

Advantages of Jasper:

• Jasper is bi-directional. Callbacks are possible (limited in levels only by memory), and queries can backtrack.