A equivalent object-oriented schema evolution approach using the path-independence language

The software legacy problem caused by schema evolution in an object-oriented database is a method of equivalent schema evolution based on a path independence (PI) language. The PI language which has been adopted in some systems raises the level of abstraction for behavioral schema design and is almost independent of the specific schema digraph. We develop the PI language and advocate an equivalent schema evolution method which not only resolves the software reuse problem in schema evolution but also supports a schema version mechanism which is an advanced feature in database systems