CS 3430 Lecture 11: ER odds and ends, summary

• School: App State
• Department: Computer Science
• Course: CS 3430
• Professor: Mohammad Mohebbi

Document Summary

I(cid:374) a(cid:374) e with (cid:894)(cid:373)i(cid:374), (cid:373)a(cid:454)(cid:895) (cid:374)otatio(cid:374) we do(cid:374)(cid:859)t (cid:374)eed dou(cid:271)le li(cid:374)es e(cid:454)(cid:272)ept for weak e(cid:374)tities a(cid:374)d their identifying relationships. Place of cardinality numbers are opposite in (min, max) notation than the previous notation. Compare min-max notation vs. the previous one in the following two ers: Relationship types of degree 3 are called ternary (fig . a) and of degree n are called n-ary. In general, an n-ary relationship is not equivalent to n binary relationships. Constraints are harder to specify for higher-degree relationships (n > 2). Can we convert a ternary relationship to 3 binaries? (fig . b) 3 binary relationships can represent different information than a single ternary relationship. In ternary relationship (a) each instance is (st, pt, jt) that means supplier st, part pt, proj jt. In (b) instances are (sr, pr) sr can_supply pr (jq, pq) jq uses pq (sx, jx) sx supplies jx.