3830TextAnswersCh3 - Databases Illuminated Chapter 6...

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Page 3-1 Chapter 3 Answers to Review Questions 3.1 Name three sources for databases. (1) Existing data, (2) the development of new information systems, and (3) the redesign of existing databases. 3.2 What is the basic premise of this and the next chapter? The basic premise is that we have received one of more tables of data from some source that need to be incorporated into a new database. 3.3 Explain what is wrong with the table in Figure 3-2. PRODUCT_BUYER, the table in Figure 3-2, contains a multivalued dependency. Specifically, it contains the field CollegeMajor, which may have more than one value for each Buyer Name. 3.4 Define each of the terms listed in Figure 3-3. Term Definition Relation A table-like structure of rows and columns, where the rows store data about an entity and the columns store data about the attributes of that entity. Each column has a unique name, and all values in a column are for the same attribute. The cells in the table can only hold a single value. The order of the rows doesn’t matter, and neither does the order of the columns. The data in each row as a whole must be unique. Functional dependency A relationship between attributes in a relation where the value (or values) of one (or more) attributes determines the value (or values) of another attribute (or set of attributes). For example, the functional dependency A Æ B expresses the fact that if we know a value of A we will always know the corresponding value of B. Determinant The attribute or set of attributes that functionally determine the value of another attribute or set of attributes. The “left- hand side” of a functional dependency. For example, in the functional dependency A Æ B, A is the determinant. Candidate key An attribute or set of attributes that uniquely determines the values of all the other attributes for a row in a relation. Composite key A key that contains two or more attributes.
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Page 3-2 Term Definition Primary key The candidate key selected to be the “official” key of a relationship. Surrogate key A column of artificial data added to a relation to serve as the primary key. Foreign key The attribute (or set of attributes) that is a primary key in one table that is then placed in a second table to form a relationship to the first table by storing linking values. The term foreign key refers to the attribute or set of attributes in the second table. Referential integrity constraint A value constraint of a foreign key that states that no value can be placed in the foreign key unless it already exists as a primary key value in the linked table. Normal form One category in a set of categories (“normal forms”) used to describe relations according to the type of anomalies that can occur in the relations. Multivalued dependency
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This note was uploaded on 09/13/2009 for the course CS CS31 taught by Professor Camillo during the Spring '09 term at Grantham.

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3830TextAnswersCh3 - Databases Illuminated Chapter 6...

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