Sharing of information is limited so as to prevent unfettered information flow.
Examples include the Bell-LaPadula security model, the Biba integrity model, Denning's Lattice
models, and Cohen's POset models.
Complexity: Effectively limiting sharing with other than purely physical
means has proven to be a highly complex issue. For example, more than 20
years of effort has been put forth in the design of trusted systems to try
to achieve this goal and it appears that another 20 years will be required
before the goal is actually realized.