Schema Specification

In this chapter, the Create statement is enhanced to support the definition of validtime relations. Additionally, the Alter statement should be extended to allow these definitions to be later changed. In the language extension to be discussed shortly, we adopted the following goals. 1. Extensions should be upward compatible with current SQL2. 2. Extensions should be as minimal as possible. 3. As few reserved words as possible should be introduced. 4. Punctuation should be consistent with the rest of the language. 5. Extensions should be consistent and compatible with user-defined time syntax. 6. The clean lines of the BCDM should be retained. 7. Defaults should be carefully chosen to reflect common usage and to enable a suitable reduction proof (see (1)).