Decision time explained

In temporal databases, decision time is the time when a decision was made about a fact stored in a database. It is used to keep a history of decisions about valid times.

In a database table, the start and end time of the decision time interval can be represented by adding two table columns. This interval is closed [in the [[Upper and lower bounds|lower bound]], and open at the upper bound). When a decision has not been replaced, the end time of the decision is unknown, and it can thus be considered valid "until changed" or infinite (∞).

Valid time and decision time are ways of modeling data, and is not applicable for all types of data,[1] and transaction time is hence the most used temporal functionality. The concept of decision time can for example be used in bitemporal databases (together with valid time instead of transaction time), or in tritemporal databases.[2]

History

The term decision time was coined by Mario Nascimento and Margaret Eich (1995).[3]

Although the ISO SQL standard has included support for "application-time period tables" (valid time tables) and "system-versioned tables" (transaction tables) since, it does however not include specific clauses for decision time.

Comparison with valid time and transaction time

In a tritemporal database,[4] valid times are a history of valid time periods for facts stored in the database. The decision times are a history of decisions about validity times, and transaction times are again a history of decision times. Thus, transaction times are a history of meta-histories ("histories of histories").

Decision time is unconstrained in relationship to valid time, but it must be earlier than the transaction time. For example, the decision time can not be assigned a date in the future.

Example

The following is a list of real events that occurred between the 1964 and 1976 United States presidential elections:

DateDecision makerReal world event
1964-11-03Electoral CollegeElection of 1964
1968-11-05Electoral CollegeElection of 1968
1972-11-07Electoral CollegeElection of 1972
1973-10-10Spiro AgnewAgnew resigns
1973-10-12Richard NixonNixon nominates Ford
1973-12-06CongressCongress confirms Ford
1974-08-09Richard NixonNixon resigns
1974-08-20Gerald FordFord nominates Rockefeller
1974-12-19CongressCongress confirms Rockefeller
1976-11-02Electoral CollegeElection of 1976

In this example, a constant 7-day delay is assumed between the decision time and the transaction time when the data is committed to the database. Given those conditions, the database would have contained the following information after the election in 1976:

ValidDecisionTransaction
PresidentViceFromToFromToFromTo
JohnsonHumphrey1965-01-201969-01-201964-11-031964-11-10
NixonAgnew1969-01-201973-01-201968-11-051968-11-12
NixonAgnew1973-01-201977-01-201972-11-071972-11-141973-10-17
NixonAgnew1973-01-201977-01-201972-11-071973-10-101973-10-17
NixonAgnew1973-01-201973-10-101973-10-101973-10-17
Nixon(Vacant)1973-10-101977-01-201973-10-101973-10-171973-12-13
NixonFord1977-01-201973-10-121973-10-191973-12-13
Nixon(Vacant)1973-10-101977-01-201973-10-101973-12-061973-12-13
Nixon(Vacant)1973-10-101973-12-061973-12-061973-12-13
NixonFord1977-01-201973-10-121973-12-061973-12-13
NixonFord1973-12-061977-01-201973-12-061973-12-131974-08-15
NixonFord1973-12-061977-01-201973-12-061974-08-081974-08-15
NixonFord1973-12-061974-08-091974-10-081974-08-15
Ford(Vacant)1974-08-091977-01-201974-10-081974-08-151974-12-26
FordRockefeller1977-01-201974-10-201974-08-271974-12-26
Ford(Vacant)1974-08-091977-01-201974-10-081974-12-191974-12-26
Ford(Vacant)1974-08-091974-12-191974-12-191974-12-26
FordRockefeller1977-01-201974-08-201974-12-191974-12-26
FordRockefeller1974-12-191977-01-201974-12-191974-12-26
CarterMondale1977-01-201981-01-201976-11-021976-11-09
Given the 7-day delayed table above, the question "who was president and vice president for the valid time of 1977-01-01" (which given the 7-day delay could provide data for 1976-12-25) would be:

See also

Notes and References

  1. Web site: Sehn . Tim . 2023-08-07 . So you want a Temporal Database? DoltHub Blog . 2024-02-10 . en.
  2. Web site: A SURVEY ON TEMPORAL DATA AND ITS RELATED CONCEPTS - S.SENTHILARASI, Research Scholar Department of Computer Science, Vels Institute of Science, Technology & Advanced Studies (VISTAS) Dr.S.Kamalakkannan, Associate Professor Department of Information Technology Vels Instituteof Science, Technology & Advanced Studies (VISTAS).
  3. Mario A. Nascimento, Margaret H. Eich, “Decision Time in Temporal Databases”, In Proceedings of the Second International Workshop on Temporal Representation and Reasoning, 1995, pp. 157-162
  4. Web site: Semantics of Temporal Models With Multiple Temporal Dimensions - Peter Kraft and Jens Otto Sørensen, Aarhus School of Business, Denmark .