6.21

Consider the E-R diagram in Figure 6.30, which models an online bookstore.

1. Suppose the bookstore adds Blu-ray discs and downloadable video to its collection. The same item may be present in one or both formats, with differing prices. Draw the part of the E-R diagram that models this addition, show just the parts related to video.

2. Now extend the full E-R diagram to model the case where a shopping basket may contain any combination of books, Blu-ray discs, or downloadable video.
   

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Note that Blu_ray_discs and downloadable_videos are weak entities while video_in_bluray and video_on_net are the identifying relationships sets. video is the identifying entity set and owns both of the weak entities.