Tuple-versioning (also called point-in-time) is a mechanism used in a relational database management system to store past states of a relation. A Relational database management system (RDBMS is a Database management system (DBMS that is based on the Relational model as introduced by E Normally, only the current state is captured.
Using tuple-versioning techniques, typically two values for time are stored along with each tuple: a start time and an end time. In Mathematics, a tuple is a Sequence (also known as an "ordered list" of values called the components of the tuple These two values indicate the validity of the rest of the values in the tuple.
Typically when tuple-versioning techniques are used, the current tuple has a valid start time, but a null value for end time. Therefore, it is easy and efficient to obtain the current values for all tuples by querying for the null end time.
A single query that searches for tuples with start time less than, and end time greater than, a given time (where null end time is treated as a value greater than the given time) will give as a result the valid tuples at the given time.
For example, if a person's job changes from Engineer to Manager, there would be two tuples in an Employee table, one with the value Engineer for job and the other with the value Manager for job. A table is both a mode of Visual communication and a means of arranging Data. The end time for the Engineer tuple would be equal to the start time for the Manager tuple.
See also
References
- Comparison of Access Methods for Time-Evolving Data, by Betty Salzberg and Vassilis J. A temporal database is a Database with built-in time aspects e Bitemporal data is a concept used in a Temporal database. It denotes both the Valid time and Transaction time of the data Tsotras, ACM Computing Surveys, Vol. The Association for Computing Machinery, or ACM, was founded in 1947 as the world's first scientific and educational Computing society 31, No. 2, June 1999.
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic