Mode Decomposition---The method of judging non-destructive connectivity

Example: Known r<u, f>,u= {A, B, C, D, E},f={ab→c, D→e, c→d},r a decomposition ρ= {R1 (a,b,c), R2 (C,d), R3 (D,e)}. Determines whether the decomposition ρ is a lossless connection decomposition.

Solution: (1) construct the initial table:

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Relational schema R<u, a decomposition of f> ρ= {r1<u1,f1>,r2<u2,f2>}.

What if U1∩U2→U1-U2? f+ or u1∩u2→u2-u1? f+, then ρ has a non-destructive connectivity.

This theorem can be used to determine the non-destructive connectivity of mode decomposition in Split

Example: Student relations S (Sno, Sname, Ssex, Dept, Deptmanager) decomposed into S (Sno, Sname, Ssex, sdept) and D (Dept, Deptmanager), D∩s = Dept, D-s = d Eptmanager, Dept→deptmanager is a function dependency in the original relationship, and this decomposition is the decomposition of a lossless connection.

Mode Decomposition---The method of judging non-destructive connectivity (RPM)