Schema evolution


In computer science, schema versioning and schema evolution, deal with the need to retain current data and software system functionality in the face of changing database structure. The problem is not limited to the modification of the schema. It, in fact, affects the data stored under the given schema and the queries posed on that schema.
A database design is sometimes created as a "as of now" instance and thus schema evolution is not considered.. This assumption, almost unrealistic in the context of traditional information systems, becomes unacceptable in the context of systems that retain large volumes of historical information or those such as Web Information Systems, that due to the distributed and cooperative nature of their development, are subject of an even stronger pressure toward change. Due to this historical heritage the process of schema evolution is nowadays a particularly taxing one. It is, in fact, widely acknowledged that the data management core of an applications is one of the most difficult and critical components to evolve. The key problem is the impact
of the schema evolution on queries and applications. As shown in each evolution step might affect up to 70% of the queries operating on the schema, that must be manually reworked consequently.
The problem has been recognized as a pressing one by the database community for more than 12 years. Supporting Schema Evolution is a difficult problem involving complex mapping among schema versions and the tool support has been so far very limited. The recent theoretical advances on mapping composition and mapping invertibility, which represent the core problems underlying the schema evolution remains almost inaccessible to the large public. The issue is particular felt by temporal databases.

Related works