Editing Consistency (database systems) (section)

==As an ACID guarantee==
Consistency is one of the four guarantees that define [[ACID]] [[database transaction|transactions]]; however, significant ambiguity exists about the nature of this guarantee. It is defined variously as:
* The guarantee that [[Relational database#Constraints|database constraints]] are not violated, particularly once a transaction commits.<ref name="Haerder & Reuter">{{cite journal | url=http://www.minet.uni-jena.de/dbis/lehre/ws2005/dbs1/HaerderReuter83.pdf | archive-url=http://web.archive.org/web/20170907170115/http://www.minet.uni-jena.de/dbis/lehre/ws2005/dbs1/HaerderReuter83.pdf | archive-date=2017-09-07 | title=Principles of Transaction-Oriented Database Recovery |author1=Haerder, T |author2=Reuter, A. | journal=Computing Surveys |date=December 1983  | volume=15 | issue=4 | pages=287–317| doi=10.1145/289.291 | s2cid=207235758 }}</ref><ref>{{cite web|url=http://databases.about.com/od/specificproducts/a/acid.htm|title=The ACID Model|author=Mike Chapple|work=About|access-date=2014-07-23|archive-date=2016-12-29|archive-url=https://web.archive.org/web/20161229001436/http://databases.about.com/od/specificproducts/a/acid.htm|url-status=dead}}</ref><ref>{{cite web|url=http://msdn.microsoft.com/en-us/library/aa480356.aspx|title=ACID properties}}</ref><ref>{{cite web|url=http://www.techopedia.com/definition/23949/atomicity-consistency-isolation-durability-acid|title=What is ACID in Databases? - Definition from Techopedia|author=Cory Janssen|work=Techopedia.com}}</ref><ref>{{cite web|url=http://www.iso.org/iso/home/store/catalogue_ics/catalogue_detail_ics.htm?csnumber=27614|title=ISO/IEC 10026-1:1998 - Information technology -- Open Systems Interconnection -- Distributed Transaction Processing -- Part 1: OSI TP Model}}</ref>
* The guarantee that any transactions started in the future necessarily see the effects of other transactions committed in the past.<ref name="CAP Theorem Paper">{{cite web |url=http://www.glassbeam.com/sites/all/themes/glassbeam/images/blog/10.1.1.67.6951.pdf |title=Brewer's Conjecture and the Feasibility of Consistent, Available, Partition-Tolerant Web Services |url-status=dead |archive-url=https://web.archive.org/web/20190629112250/https://www.glassbeam.com/sites/all/themes/glassbeam/images/blog/10.1.1.67.6951.pdf |archive-date=2019-06-29}}</ref><ref name="Ports et al">{{cite journal | url=http://drkp.net/papers/txcache-osdi10.pdf | title=Transactional Consistency and Automatic Management in an Application Data Cache |author1=Ports, D.R.K. |author2=Clements, A.T. |author3=Zhang, I. |author4=Madden, S. |author5=Liskov, B. | journal=Mit Csail}}</ref>

As these various definitions are not mutually exclusive, it is possible to design a system that guarantees "consistency" in every sense of the word, as most [[relational database management system]]s in common use today arguably do.