Questions and Answers
Define the term 'relation' in the context of the relational data model mentioned in the text.
A named two-dimensional table of data.
What is a 'primary key' in the context of a relation in a database?
An attribute or a combination of attributes that uniquely identifies each row in a relation.
Explain the concept of a 'composite key' in the context of a database relation.
A primary key that consists of more than one attribute.
What is the role of a 'foreign key' in a relation within a database?
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What are the properties of relations in a database according to the text?
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Study Notes
Relations and Keys in a Database
Relations
- A relation represents a table in a relational database, consisting of rows (tuples) and columns (attributes).
Primary Key
- A primary key is a column or set of columns in a relation that uniquely identifies each row (tuple) in the table.
Composite Key
- A composite key is a primary key composed of more than one column, where the combination of values is unique for each row.
Foreign Key
- A foreign key is a field in a relation that refers to the primary key of another relation, establishing a relationship between the two tables.
Properties of Relations
- Relations in a database have the following properties:
- Each row is unique
- Each column has a unique name
- All rows have the same number of columns
- The order of columns is significant
- The order of rows is insignificant
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