Editing Temporal database (section)

==Schema evolution==
{{Main article|Schema evolution}}
A challenging issue is the support of temporal queries in a transaction time database under evolving [[database schema|schema]]. In order to achieve perfect archival quality it is of key importance to store the data under the schema version under which they first appeared. However, even the most simple temporal query rewriting the history of an attribute value would be required to be manually rewritten under each of the schema versions, potentially hundreds as in the case of [[MediaWiki]].<ref>[http://yellowstone.cs.ucla.edu/schema-evolution/index.php/Schema_Evolution_Benchmark Schema Evolution Benchmark - Schema Evolution]</ref> This process would be particularly taxing for users. A proposed solution is to provide automatic query rewriting,<ref name="curino-vldb-prima2008">{{cite conference| title=Managing and querying transaction-time databases under schema evolution |author1=Hyun J. Moon |author2=Carlo A. Curino |author3=Alin Deutsch |author4=C.-Y. Hou |author5=Carlo Zaniolo |name-list-style=amp | conference= Very Large Data Base VLDB | year = 2008 | url = http://yellowstone.cs.ucla.edu/schema-evolution/index.php/Prima }}</ref><ref name="curino-sigmod-aims2010">{{cite conference | title=Scalable Architecture and Query Optimization for Transaction-time DBs with Evolving Schemas |author1=Hyun J. Moon |author2=Carlo A. Curino |author3=Carlo Zaniolo |name-list-style=amp | conference= SIGMOD | year = 2010 | url = http://yellowstone.cs.ucla.edu/schema-evolution/index.php/AIMS }}</ref> although this is not part of SQL or similar standards.

Approaches to minimize the complexities of [[schema evolution]] are to: 
* Use a [[Semi-structured model|semi-structured database]]/[[NoSQL]] database which reduces the complexities of modeling attribute data but provides no features for handling multiple time axes.<ref name="mlw-talk-why-banks-need-bitemporal-2015">{{cite conference | title=Why Banks Care About Bitemporality | author=Anthony B. Coates | conference=MarkLogic World 2015 | year=2015 | url=https://www.youtube.com/watch?t=28&v=n29Gtit3lMU}}</ref>
* Use a database capable of storing both [[semi-structured data]] for attributes and [[structured data]] for time axes (e.g., [[Snowflake Inc.|SnowflakeDB]], [[PostgreSQL]])