Editing Polyinstantiation (section)

== Database ==
In databases, polyinstantiation is database-related [[SQL]] (structured query language) terminology. It allows a relation to contain multiple rows with the same primary key; the multiple instances are distinguished by their security levels.<ref>{{cite web
| url=http://www.acsac.org/secshelf/book001/21.pdf
| title=Solutions to the Polyinstantiation Problem
| first1=Sushil
| last1=Jajodia
| first2=Ravi S
| last2=Sandhu
| first3=Barbara T.
| last3=Blaustein
| date=2006-02-01}}</ref> It occurs because of mandatory policy. Depending on the security level established, one record contains sensitive information, and the other one does not, that is, a user will see the record's information depending on his/her level of confidentiality previously dictated by the company's policy<ref>{{cite book
| title=Security in Computing
| url=https://archive.org/details/securityincomput0003pfle
| url-access=registration
| first1=Charles P.
| last1=Pfleeger
| first2=Shari Lawrence
| last2=Pfleeger
| year=2003
| publisher=[[Prentice Hall]] Professional
| isbn=9780130355485}}</ref>

Consider the following table, where the primary key is '''Name''' and '''[[λ]](x)''' is the security level:

{| class="wikitable"
|-
! Name
! λ(Name)
! Age
! λ(Age)
! λ
|-
| Alice
| Secret
| 18
| Top Secret
| Top Secret
|-
| Bob
| Secret
| 22
| Secret
| Secret
|-
| Bob
| Secret
| 33
| Top Secret
| Top Secret
|-
| Trudy
| Top Secret
| 15
| Top Secret
| Top Secret
|}

Although useful from a security standpoint, polyinstantiation raises several problems:
* Moral scrutiny, since it involves lying
* Providing consistent views
* Explosion in the number of rows