Figure 9-17: Identifying basic operations. Figure 9-18 goes (Web design service)
Figure 9-17: Identifying basic operations. Figure 9-18 goes just a little further by establishing relationships between the different operations described in Figure 9-17. In other words, musicians play instruments and have skills. Bands are usually of a specific genre. Both musicians and bands can place classified ads to advertise themselves. Figure 9-18: Linking the basic operations. Figure 9-19 shows a briefly constructed ERD as an application of business rules to the operational diagram shown in Figure 9-18. There are a number of important points to note: . Musicians can play multiple instruments. . Musicians can be multi-skilled. . A band can have multiple genres. . The MEMBERS field in the band table takes into account the one-to-many relationship between BAND and MUSICIAN. In other words, there is usually more than one musician in a band; however, a musician doesn t necessarily have to be in a band, a band may be broken up and have no musicians, and both bands and musicians can advertise. . Musicians and bands can place advertisements. Instrument Genre Musician Classified Ad Band Skill Instrument Musician Skill Genre Band Classified Ad 242 Chapter 9
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