CS240A: Databases and Knowledge Bases Temporal Databases Carlo Zaniolo Department of Computer Science University of California, Los Angeles

The Problem is Harder than you think  No support for temporal queries in SQL,  although information in real life tend to be time-stamped and my applications re temporal in nature  Temporal Events (date of accident), vs.  and temporal states (the state of being an employee in a company— duration, besides start event and end event).  Many research approaches proposed but no commercial extension  Extending SQL (and SQL-2 in particular) is an Herculean task  Temporal DBs come in three main types: transaction time, valid time, and bi-temporal. Each require a specialized treatment.  These issues pose challenges at the logical level (data representation and queries)  but significant challenges also occur at the physical level:  efficient storage, indexing techniques and query optimization techniques are needed.

Time in History  As today, there is a poor understanding of temporal issues and their complexities among database specialists  This parallels the general ignorance about time we find in modern life, where the solutions of all temporal problems are taken for granted  But finding efficient ways to represent and measure time have created major technical and social challenge to civilizations for thousands of years.

Time Changes Everything  Temporal extensions based on TSQL2 included in the SQL standards in 2011  Two DBMS vendors (IBM and Teradata) have recently announced support for bi-temporal DBs in their databases  Transaction Time is called System Time  Valid time is called Business Time  Storage and simple retrieval of bi-temporal queries is supported, but complex temporal queries are not supported in DB2.