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Data Mgmt Lab_Part_6

# Data Mgmt Lab_Part_6 - 3 THE RELATIONAL MODEL Exercise 3.1...

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Unformatted text preview: 3 THE RELATIONAL MODEL Exercise 3.1 Define the following terms: relation schema, relational database schema, domain, attribute, attribute domain, relation instance, relation cardinality , and relation degree . Answer 3.1 A relation schema can be thought of as the basic information describing a table or relation . This includes a set of column names, the data types associated with each column, and the name associated with the entire table. For example, a relation schema for the relation called Students could be expressed using the following representation: Students( sid: string , name: string , login: string , age: integer , gpa: real ) There are five fields or columns, with names and types as shown above. A relational database schema is a collection of relation schemas, describing one or more relations. Domain is synonymous with data type . Attributes can be thought of as columns in a table. Therefore, an attribute domain refers to the data type associated with a column. A relation instance is a set of tuples (also known as rows or records ) that each conform to the schema of the relation. The relation cardinality is the number of tuples in the relation. The relation degree is the number of fields (or columns) in the relation....
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Data Mgmt Lab_Part_6 - 3 THE RELATIONAL MODEL Exercise 3.1...

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