13_1 Advanced Data Types and New Applications

13_1 Advanced Data Types and New Applications - 1 Temporal...

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2 Temporal Data Spatial and Geographic Databases Multimedia Databases Mobility and Personal Databases
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3 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.
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4 Example of a temporal relation: Temporal query languages have been proposed to simplify modeling of time as well as time related queries.
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5 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 Felds of date and time , with six fractional digits for the seconds Feld. T imes are speciFed in the Universal Coordinated Time , abbreviated UTC (from the ±rench); supports time with time zone . interval : refers to a period of time (e.g., 2 days and 5 hours), without specifying a particular time when this period starts; could more accurately be termed a span .
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6 Predicates precedes, overlaps, and contains on time intervals. Intersect can be applied on two intervals, to give a single (possibly empty) interval; the union of two intervals may or may not be a single interval. A snapshot of a temporal relation at time t consists of the tuples that are valid at time t, with the time-interval attributes projected out. Temporal selection : involves time attributes Temporal projection : the tuples in the projection inherit their time-intervals from the tuples in the original relation. Temporal join : the time-interval of a tuple in the result is the intersection of the time-intervals of the tuples from which it is derived. It intersection is empty, tuple is discarded from join.
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7 Functional dependencies must be used with care: adding a time feld may invalidate ±unctional dependency A temporal functional dependency x Y holds on a relation schema R i±, ±or all legal instances r o± R, all snapshots o± r satis±y the ±unctional dependency X Y. SQL:1999 Part 7 (SQL/Temporal) is a proposed extension to SQL:1999 to improve support o± temporal data. τ
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9 Spatial databases store information related to spatial locations, and support efFcient storage, indexing and querying of spatial data. Special purpose index structures are important for accessing
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This note was uploaded on 01/24/2011 for the course CS 585 at USC.

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13_1 Advanced Data Types and New Applications - 1 Temporal...

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