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Object-oriented database systems were proposed to solve the
difficulties encountered in traditional databases, such as
deal with complex structures and recursively-defined
persistent objects, active database components, and support
browsing and complex queries. We will describe a small
library in Prolog. This library provides an object-
oriented environment which can maintain persistent,
complex data components. This environment combines the
advantages of both object-oriented concepts and a logic
programming language. We call this environment which is
about 1200 lines of Prolog code. There are some
advantages for this approach. First, the database language
in MODEL_OODB is like logic programming; it is a
declarative language, so it supports data abstraction.
Second, there is an inference engine in Prolog, and the
MODEL_OODB has a built-in deductive capability. Third,
the performance of Prolog's hashing function is not
bad, it is very helpful for doing dynamic binding in
MODEL_OODB. In the user environment, MODEL_OODB provides an
operation mode which is like that of the UNIX file system.
It can easily solve name conflict problems, so it is not
confused for its distributed consult files. The
distributed consulting of MODEL_OODB uses remote coyp of
the remote file into local host. If the user locks the remote
file, then no others can update it until it is unlocked.
Our locking mechanism uses UNIX shell commands or UNIX
remote shell commands. It provides a simple lock mechanism
to permit users to be sure that no more than one user are
updating the shared data simultaneously.
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