Technical Report Number
In multilevel security there is a hierarchy of users or user-levels, in which each user has its own version of information. Most of the existing multilevel secure (MLS) data models support u-polyinstantiation. The only model that supports key-polyinstantiation was proposed by Gadia et al[GS1998, JS1990, CG1995], but work on it remains incomplete. It is important for a model to support key-polyinstantiation because in the real world it is often the case that an object varies in its key value(s) (such as name, SSN, identification number etc.) when it occurs in the beliefs of different users. Thus having a unique key across beliefs limits our ability to accurately model the real world. Our work focuses on the relational database model, supports key-polyinstantiation and has semantics defined in an SQL-like format since most database users are experienced in using SQL and hence such semantics are intuitive and easy to understand.