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A discussion of multi-valued attributes in a database

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What two courses of action are available to designer encountering a multivalued attribute?


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A multi-valued attribute is an attribute in an entity that can contain multiple values. This in in contrast to single-value attributes that contain a single value. An example of a multi-value attribute is the "hobbies" attribute for an "employee" entity. It is expected that an employee can have more than one hobby.

Database designers have two approaches available when dealing with multi-valued attributes. The first, and simplest approach is to simply put all of the values in a single fields, separated by a delimiter. Continuing with our "hobbies" example, we could create values like: "biking, fishing, reading" or "dining, riding". The appeal using this approach is that it is simple and requires no additional database structure. The difficulty of this approach is that it eliminates much of the power of ...

Solution Summary

This solution explains what multi-valued attributes are and the different options for handling them in the design of a database.

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Database systems - conversion: unnormalized relation, 1NF, 2NF, 3NF

Nazca Cinemas is a small movie theater that would like you to design a movie scheduling database system for them. The theater has four rooms (screens). Each room has its own unique ID and the seating capacity and screen size for each are recorded. Each movie is assigned a unique movie ID and its title and runtime are recorded.

Assume the following:

A movie can be shown more than once on a given date.
A movie can be shown more than once in a given room.
A movie can be shown in more than one room simultaneously.
Several showings can be booked at different start times in a given room on a given date.

The following unnormalized relation has been developed based on this case. Do not add any additional attributes.

SHOWING (MovieID, Title, Runtime, RoomID, ScreenSize, Capacity, Date, StartTime)

1. Convert the unnormalized relation into 1NF and briefly discuss the changes that were necessary.
2. Convert the 1NF relation to 2NF and briefly discuss the changes that were necessary.
3. Convert the 2NF relation to 3NF and briefly discuss the changes that were necessary.

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