Editing Transaction time

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In [[temporal database]]s, '''transaction time''' is the time when some data has been [[Data loading|loaded]] into a [[database]]. The time when a transaction is valid can be called the '''transaction time-period'''. It is a technical timeline controlled by a [[Data integration|integration layer]] (for example a [[data warehouse]]).<ref name=":0">{{cite news |title=A gentle introduction to bitemporal data challenges - Roelant Vos |newspaper=Roelant Vos |date=20 February 2023 |url=https://roelantvos.com/blog/a-gentle-introduction-to-bitemporal-data-challenges/}}<!-- auto-translated from Danish by Module:CS1 translator --></ref> More formally, it is the [[point-in-time table|point-in-time]] during which a fact stored in the database is considered to be true.

The period is an interval based on [[Timestamp|load times]] (called '''load datetime''' in [[data vault modeling|data vault]]<ref name=":0" /><ref>{{cite web |access-date=2024-02-10 |title=Transactional Links - AutomateDV |url=https://automate-dv.readthedocs.io/en/latest/tutorial/tut_t_links/ |work=automate-dv.readthedocs.io}}<!-- auto-translated from Danish by Module:CS1 translator --></ref>), also called '''inscription timestamp'''.<ref name=":0" /> Other names of the interval is '''assertion timeline'''<ref name=":1">{{cite news |title=A not-so-gentle follow-up on bitemporal data challenges - Roelant Vos |newspaper=Roelant Vos |date=23 March 2023 |url=https://roelantvos.com/blog/a-not-so-gentle-follow-up-on-bitemporal-data-challenges/}}<!-- auto-translated from Danish by Module:CS1 translator --></ref>), '''[[State (computer science)|state timeline]]'''<ref name=":1" />) or '''technical timeline'''.<ref name=":1" /> [[SQL:2011]] has support for transaction time through so-called '''system-versioned tables'''.<ref>{{cite web |access-date=2024-06-18 |date=2023-10-16 |language=en-us |surname=rwestMSFT |title=Temporal Tables - SQL Server |url=https://learn.microsoft.com/en-us/sql/relational-databases/tables/temporal-tables?view=sql-server-ver16 |work=learn.microsoft.com}}<!-- auto-translated from Danish by Module:CS1 translator --></ref><ref>{{cite web |access-date=2024-06-18 |title=System-Versioned Tables |url=https://mariadb.com/kb/en/system-versioned-tables/ |work=MariaDB KnowledgeBase}}<!-- auto-translated from Danish by Module:CS1 translator --></ref><ref>{{cite web |access-date=2024-06-18 |title=SAP Help Portal |url=https://help.sap.com/docs/SAP_HANA_PLATFORM/6b94445c94ae495c83a19646e7c3fd56/91302b26f62c4433bbc58e0a951cdc1d.html |work=help.sap.com}}<!-- auto-translated from Danish by Module:CS1 translator --></ref><ref>{{cite web |access-date=2024-06-18 |language=en-us |title=System-period temporal tables |url=https://www.ibm.com/docs/en/db2/11.1?topic=tables-system-period-temporal |work=www.ibm.com}}<!-- auto-translated from Danish by Module:CS1 translator --></ref> 

For many reasons, transaction time (when data arrives from a [[System of record|source system]]) is almost always different from [[valid time]] (when the event happened in the real world). For a data warehouse to unambiguously report what actually happened in the past it must be able to combine these two timelines.<ref name=":0" /> In [[Bitemporal modeling|bitemporal]] data models, valid-time and transaction time can be represented two-dimensionally in a [[Cartesian coordinate system]]. When data is delivered from the integration layer and is to be presented in a presentation layer (often in a [[Dimensional modeling|dimensional model]] or [[Wide and narrow data|wide table]]) it is often desirable to have the data on only one timeline.

In a database table, the transaction time is often represented as an interval allowing the system to "remove" entries by using two table-columns <code>start_tt</code> and <code>end_tt</code>. The time interval is [[closed set|closed]] <code>[</code> at its [[lower bound]] and [[open set|open]] <code>)</code> at its [[upper bound]].<ref>Kedar, S. V. (2013). Database management systems. Pune, India: Technical Publications.</ref> When the ending transaction time is unknown, it may be considered as <code>until_changed</code>. Academic researchers and some [[relational database management systems]] (RDBMS) have represented <code>until_changed</code> with the largest timestamp supported or the keyword <code>forever</code>. This convention is a technical [[workaround]], and not technically precise.

== History ==
The term transaction time was coined by [[Richard T. Snodgrass]] and his doctoral student Ilsoo Ahn (1986).<ref>{{Cite journal | last1 = Snodgrass | last2 = Ilsoo Ahn | title = Temporal Databases | journal = Computer | volume = 19 | issue = 9 | pages = 35 | year = 1986 | doi = 10.1109/MC.1986.1663327| url = http://www2.cs.arizona.edu/~rts/pubs/Computer.pdf }}</ref>

As of December 2011, ISO/IEC 9075, Database Language [[SQL:2011]] Part 2: SQL/Foundation included clauses in table definitions to define "system-versioned tables" (that is, transaction-time tables).

==See also==
* [[Valid time]], when an event in a database happened in the real world
* [[Decision time]], when a decision was made about interpretation of history in a database
* [[Temporal database#Using transaction time|Using transaction time]]

==References==
{{Reflist}}

{{Database models}}

{{DEFAULTSORT:Transaction Time}}
[[Category:Database management systems]]
[[Category:Transaction processing]]

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