July 2010
Intermediate to advanced
976 pages
30h 19m
English
Content preview from Information Modeling and Relational Databases, 2nd Edition
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10.3. Temporality
In the database community, various proposals and products have been developed to address temporal data. For example, SQL/Temporal was considered as a temporal extension to SQL (on hold since late 2001, but might be revived) and many DBMS products have incorporated specific support for temporal features. Three basic temporal data types may be distinguished (Snodgrass 2000):
Instant (point in time, e.g., 2008 June 3, 2:50 p.m. UTC)
Interval (duration of time, e.g., 3 weeks)
Period (anchored duration of time, e.g., 2008 June 3 ... 2006 June 23 MST)
For each of these data types, various temporal operators may be defined. For example, date subtraction (–) applied to an ordered pair of dates (e.g. today and your birthdate) results ...
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