Temporally Enhanced Database Design

The design of appropriate database schemas is critical to the effective use of database technology and the construction of effective information systems that exploit this technology. The temporal aspects of database schemas are often particularly complex and thus difficult and error-prone to design. This chapter focuses on the temporal aspects of database schemas. Its contributions are twofold. First, a comprehensive set of concepts are presented that capture temporal aspects of schemas. Second, the use of these concepts for database design is explored. Specifically, the chapter provides new guidelines for the design of (temporal) relational databases. The chapter first generalizes conventional functional dependencies to apply to temporal databases, leading to temporal keys and normal forms. Time patterns identify when attributes change values and when the changes are recorded in the database. Lifespans describe when attributes have values. The temporal support and precision of attributes indicate the temporal aspects that are relevant for the attributes and with what temporal granularity the aspects are to be recorded. And derivation functions describe how the values of an attribute for all times within its lifespan are computed from stored values. The implications of these concepts for database design are explored.