A taxonomy of changes in schema evolution

Schema evolution is the ability of a database system to respond to changes in the real world by allowing the schema to evolve. Two main categories of research work on schema evolution exist in literature; the changes-based and the tgd-based (target generating dependencies that represent mappings between elements). The tgd-based work is more recent and is mainly based on the use of composition and inversion operators to manage schema evolution. This body of work has established different combinations of tgds that may be formed as a result of a particular schema change, like LAV to GAV. The change in type of mapping (tgd) is then handled by use of inversion and composition operators. However, these operators have not been tested for different types of schema changes. This requires the merging of two aforementioned categories of work on schema evolution which is the focus of this paper. This work provides a basis for studying the applicability of inversion and composition operators on different schema changes falling in each tgd-based category thus helps to deal schema evolution in a better way.