Section 21.14 Glossary

Glossary Glossary

Attribute.

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One of the values within a tuple. More commonly called a “column” or “field”.

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Constraint.

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When we tell the database to enforce a rule on a field or a row in a table. A common constraint is to insist that there can be no duplicate values in a particular field (i.e., all the values must be unique).

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Cursor.

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A cursor allows you to execute SQL commands in a database and retrieve data from the database. A cursor is similar to a socket or file handle for network connections and files, respectively.

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Database Browser.

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A piece of software that allows you to directly connect to a database and manipulate the database directly without writing a program.

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Foreign Key.

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A numeric key that points to the primary key of a row in another table. Foreign keys establish relationships between rows stored in different tables.

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Database Index.

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Additional data that the database software maintains as rows and inserts into a tables to make lookups very fast.

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Logical Key.

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A key that the “outside world” uses to look up a particular row. For example in a table of user accounts, a person’s email address might be a good candidate as the logical key for the user’s data.

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Normalization.

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Designing a data model so that no data is replicated. We store each item of data at one place in the database and reference it elsewhere using a foreign key.

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Primary Key.

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A numeric key assigned to each row that is used to refer to one row in a table from another table. Often the database is configured to automatically assign primary keys as rows are inserted.

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Relation.

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An area within a database that contains tuples and attributes. More typically called a “table”.

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Database Tuple.

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A single entry in a database table that is a set of attributes. More typically called a “row”.

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