Explain the project-join normal form, Database Management System

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Explain the Project-Join normal form

A relation R is in PJNF along with respect to a set of functional dependencies D if for all join dependencies of the outline *(R₁, R₂, ...,R_n) and R = R₁ U R₂ U ..., UR_n at least one of the subsequent holds:

*(R₁, R₂, ...,R_n) is trivial

Each R_i is a superkey of R

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