Schema Evolution publication categorizer

In practice, any database management system sometimes needs reorganization, that is, a change in some
aspect of the logical and/or physical arrangement of a database. In traditional practice, many types of reorganization
have required denying access to a database (taking the database offline) during reorganization.
Taking a database offline can be unacceptable for a highly available (24-hour) database, for example, a
database serving electronic commerce or armed forces, or for a very large database. A solution is to reorganize

The life of a modern Information System is often characterized by (i) a push toward integration with other systems, and (ii) the evolution of its data management core in response to continuously changing application requirements. Most of the current proposals dealing with these issues from a database perspective rely on the formal notions of mapping and query rewriting.

While the contents of databases can be easily changed, their organization is typically extremely rigid. Some databases relax the rigidity of database organization somewhat by supporting simple changes to individual schemas. As described in this paper, OTGen supports not only more complex schema changes, but also database reorganization. A database administrator uses a declarative notation to describe mappings between objects created with old versions of schemas and their corresponding representations using new versions.

The days when a company could take its system offline for any kind of maintenance are rapidly disappearing. As businesses become global and move toward e-commerce, systems now have to be highly available because the cost of outage for corporations involved in e-commerce can easily reach millions of dollars per hour. Today, it is unlikely that the customer will come back if your systems are unavailable, they will simply give that business to your competitor whose systems are online.

DB2 V8 begins the process of making it easier to implement database changes with fewer steps and less downtime. IBM calls the changes being made to DB2 to facilitate simpler and quicker database changes \"online schema evolution\". For example, as of V8, you can change a CHAR column to a larger size simply using ALTER. The remainder of this article will focus on the improved schema changes supported by DB2 Version 8.

The evolution of an information system is reflected in data modeling by database reorganization. Entity-Relationship (ER) consistency expresses the capability of relational databases to model information oriented systems. A relational schema consisting of relational schemes, together with key and inclusion dependencies, is said to be ER-consistent if it complies with an entity-relationship structure, meaning that it is representableby an ER-Diagram.