Polyinstantiation

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Polyinstantiation in the information technology world 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. It occurs because of mandatory policy.

Consider the following table, where primary key is Name and ʎ(x) is the security level:

Name	ʎ(Name)	Age	ʎ(Age)	ʎ
Alice	S	18	TS	TS
Blob	S	22	S	S
Blob	S	33	TS	TS
Trudy	TS	15	TS	TS

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;

In cryptography, polyinstantiation is the existence of a cryptographic key in more than one secure physical location.