Editing Temporal database (section)

===Using three axes: valid time, decision time, and transaction time===
[[Decision time]] is an alternative to the transaction time period for recording the time at which a database entry may be accepted as correct. This enables queries that show the officially recognized facts at a given time, even if there was a delay in committing those facts to the database. Support for decision time preserves the entire history and prevents the loss of information during updates.<ref>Mario A. Nascimento, Margaret H. Eich, “[http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.50.8187 Decision Time in Temporal Databases]”, In ''Proceedings of the Second International Workshop on Temporal Representation and Reasoning'', 1995, pp. 157-162</ref>

Decision time periods can only occur in the past or up to the transaction time. As in a transaction time table, records are never deleted. Only new records can be inserted, and existing ones updated by setting their decision end time to show that they are no longer current.

To enable decision time, two more fields are added to a database table: <code>decision_from</code> and <code>decision_to</code>. Here, <code>decision_from</code> is the time a decision was made, and <code>decision_to</code> is the time that the decision was superseded (which may be infinity if it has not yet been superseded). When combined with transaction time, this makes the table into a [[#Tritemporal_relations|tritemporal table]].
The following is a list of real events that occurred between the 1964 and 1976 [[United States presidential election]]s:
{| class="wikitable" 
!Date
!Decision maker
!Real world event
|-
|1964-11-03
|[[United States Electoral College|Electoral College]]
|[[1964 United States presidential election|Election of 1964]]
|-
|1968-11-05
|Electoral College
|[[1968 United States presidential election|Election of 1968]]
|-
|1972-11-07
|Electoral College
|[[1972 United States presidential election|Election of 1972]]
|-
|1973-10-10
|[[Spiro Agnew]]
|[[Spiro Agnew#Criminal investigation and resignation|Agnew resigns]]
|-
|1973-10-12
|[[Richard Nixon]]
|[[Gerald Ford#Vice presidency (1973–1974)|Nixon nominates Ford]]
|-
|1973-12-06
|[[United States Congress|Congress]]
|Congress confirms Ford
|-
|1974-08-09
|Richard Nixon
|[[Richard Nixon#Resignation|Nixon resigns]]
|-
|1974-08-20
|[[Gerald Ford]]
|[[Nelson Rockefeller#Vice President of the United States (1974–1977)|Ford nominates Rockefeller]]
|-
|1974-12-19
|Congress
|Congress confirms Rockefeller
|-
|1976-11-02
|Electoral College
|[[1976 United States presidential election|Election 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:
{| class="wikitable"
| colspan="2" |
! colspan="2" |Valid
! colspan="2" |Decision
! colspan="2" |Transaction
|-
!President
!Vice
!From
!To
!From
!To
!From
!To
|- style="border-bottom:double"
|Johnson
|Humphrey
|1965-01-20
| style="color:red" |1969-01-20
|1964-11-03
|∞
|1964-11-10
|∞
|- style="border-bottom:double"
|Nixon
|Agnew
| style="color:red" |1969-01-20
| style="color:orange" |1973-01-20
|1968-11-05
|∞
|1968-11-12
|∞
|- style="border-bottom:double"
|Nixon
|Agnew
| style="color:orange" |1973-01-20
|1977-01-20
|1972-11-07
|∞
|1972-11-14
| style="color:red" |1973-10-17
|-
|Nixon
|Agnew
| style="color:orange" |1973-01-20
|1977-01-20
|1972-11-07
| style="color:red" |1973-10-10
| style="color:red" |1973-10-17
|∞
|-
|Nixon
|Agnew
| style="color:orange" |1973-01-20
| style="color:lime" |1973-10-10
| style="color:red" |1973-10-10
|∞
|1973-10-17
|∞
|- style="border-bottom:double"
|Nixon
|(Vacant)
| style="color:lime" |1973-10-10
|1977-01-20
|1973-10-10
|∞
|1973-10-17
| style="color:orange" |1973-12-13
|- style="border-bottom:double"
|Nixon
|Ford
|∞
|1977-01-20
|1973-10-12
|∞
|1973-10-19
| style="color:lime" |1973-12-13
|-
|Nixon
|(Vacant)
| style="color:lime" |1973-10-10
|1977-01-20
|1973-10-10
| style="color:orange" |1973-12-06
| style="color:orange" |1973-12-13
|∞
|-
|Nixon
|(Vacant)
| style="color:lime" |1973-10-10
| style="color:green" |1973-12-06
| style="color:orange" |1973-12-06
|∞
|1973-12-13
|∞
|-
|Nixon
|Ford
|∞
|1977-01-20
|1973-10-12
| style="color:lime" |1973-12-06
| style="color:lime" |1973-12-13
|∞
|- style="border-bottom:double"
|Nixon
|Ford
| style="color:green" |1973-12-06
|1977-01-20
| style="color:lime" |1973-12-06
|∞
|1973-12-13
| style="color:green" |1974-08-15
|-
|Nixon
|Ford
| style="color:green" |1973-12-06
|1977-01-20
|1973-12-06
| style="color:green" |1974-08-08
| style="color:green" |1974-08-15
|∞
|-
|Nixon
|Ford
| style="color:green" |1973-12-06
| style="color:blue" |1974-08-09
| style="color:green" |1974-10-08
|∞
|1974-08-15
|∞
|- style="border-bottom:double"
|Ford
|(Vacant)
| style="color:blue" |1974-08-09
|1977-01-20
|1974-10-08
|∞
|1974-08-15
| style="color:blue" |1974-12-26
|- style="border-bottom:double"
|Ford
|Rockefeller
|∞
|1977-01-20
|1974-10-20
|∞
|1974-08-27
| style="color:purple" |1974-12-26
|-
|Ford
|(Vacant)
| style="color:blue" |1974-08-09
|1977-01-20
|1974-10-08
| style="color:blue" |1974-12-19
| style="color:blue" |1974-12-26
|∞
|-
|Ford
|(Vacant)
| style="color:blue" |1974-08-09
| style="color:purple" |1974-12-19
| style="color:blue" |1974-12-19
|∞
|1974-12-26
|∞
|-
|Ford
|Rockefeller
|∞
|1977-01-20
|1974-08-20
| style="color:purple" |1974-12-19
| style="color:purple" |1974-12-26
|∞
|- style="border-bottom:double"
|Ford
|Rockefeller
| style="color:purple" |1974-12-19
|1977-01-20
| style="color:purple" |1974-12-19
|∞
|1974-12-26
|∞
|-
|Carter
|Mondale
|1977-01-20
|1981-01-20
|1976-11-02
|∞
|1976-11-09
|∞
|}
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:

* Nixon/Agnew when using a decision time and transaction time of 1972-11-14
* Nixon/(Vacant) when using a decision time and transaction time of 1973-10-17
* Nixon/Ford when using a decision time and transaction time of 1974-08-08
* Ford/(Vacant) when using a decision time of 1974-08-08 and transaction time of current
* Ford/Rockefeller when using a decision time and transaction time of current