A high integrity object will be allowed to access a low integrity object, but a low integrity object will not be allowed to access a high integrity object. The write down problem of disclosure is reversed for corruption to prevent low integrity information contaminating high integrity information. Multi-level security, especially concerning protection against disclosure, is a fairly well understood problem. There are a number of books on the subject. This understanding is the result of considerable research funded by the needs of military security.
Commercial security has the same concerns as military security, but the emphasis is different.