Database Design and Relational Theory: Normal Forms and All That Jazz

© C. J. Date 2019

C. J. DateDatabase Design and Relational Theoryhttps://doi.org/10.1007/978-1-4842-5540-7_6

6. Preserving FDs

C. J. Date¹ 

(1)

Healdsburg, California, USA

 

Nature does require

Her times of preservation

—William Shakespeare: Henry VIII (1613)

Once again consider our usual suppliers relvar S. Since {SNO} is a key, that relvar is certainly subject to the FD {SNO} → {STATUS}. Thus, taking X as {SNO}, Y as {STATUS}, and Z as {SNAME,CITY}, Heath’s Theorem tells us we can decompose that relvar into relvars SNC and ST, where SNC has heading {SNO,SNAME,CITY} and ST has heading {SNO,STATUS}. Sample values for SNC and ST corresponding to the value shown for S in Figure 3-1 are shown in Figure 6-1:

Figure 6-1

Relvars SNC and ST─sample values

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