This chapter covers advanced data types and new applications, including temporal datababases, spatial and geographic databases, multimedia databases, and mobility and personal databases. This chapter is suited as a means to lay the groundwork for an advanced course. Some of the material, such as temporal and spatial data types, may be suitable for self-study in a first course. | Chapter 24: Advanced Data Types and New Applications Temporal Data Spatial and Geographic Databases Multimedia Databases Mobility and Personal Databases 1 Database System Concepts, 5th Ed. ©Silberschatz, Korth and Sudarshan Time In Databases While most databases tend to model reality at a point in time (at the ``current'' time), temporal databases model the states of the real world across time. Facts in temporal relations have associated times when they are valid, which can be represented as a union of intervals. The transaction time for a fact is the time interval during which the fact is current within the database system. In a temporal relation, each tuple has an associated time when it is true; the time may be either valid time or transaction time. A bi-temporal relation stores both valid and transaction time. 2 Database System Concepts, 5th Ed. ©Silberschatz, Korth and Sudarshan Time In Databases (Cont.) Example of a temporal relation: Temporal query languages have been proposed to simplify modeling of time as well as time related queries. 3 Database System Concepts, 5th Ed. ©Silberschatz, Korth and Sudarshan Time Specification in SQL-92 date: four digits for the year (1--9999), two digits for the month (1--12), and two digits for the date (1--31). time: two digits for the hour, two digits for the minute, and two digits for the second, plus optional fractional digits. timestamp: the fields of date and time, with six fractional digits for the seconds field. Times are specified in the Universal Coordinated Time, abbreviated UTC (from the French); supports time with time zone. interval: refers to a period of time (., 2 days and 5 hours), without specifying a particular time when this period starts; could more accurately be termed a span. 4 Database System Concepts, 5th Ed. ©Silberschatz, Korth and Sudarshan Temporal Query Languages Predicates precedes, overlaps, and contains
