A repository to store data.
The part of a database that stores the data. A table has columns or attributes, and the data stored in rows.
The columns in a table. All rows in table entities have the same attributes. For example, a customer table might have the attributes
city. Each attribute has a data type such as string, integer, or date.
The data entries in a table. Rows contain values for each attribute. For example, a row in a customer table might contain the values "Matthew Richardson," "Punt Road," and "Richmond." Rows are also known as records.
- Relational model
A model that uses tables to store data and manage the relationship between tables.
- Relational database management system
A software system that manages data in a database and is based on the relational model. DBMSs have several components described in detail in Chapter 1.
A query language that interacts with a DBMS. SQL is a set of statements to manage databases, tables, and data.
Restrictions or limitations on tables and attributes. For example, a wine can be produced only by one winery, an order for wine can't exist if it isn't associated with a customer, having a name attribute could be mandatory for a customer.
- Primary key
One or more attributes that contain values that uniquely identify each row. For example, a customer table might have the primary key of
cust ID. The
cust IDattribute is then assigned a unique value for each customer. A primary key is a constraint of most tables.
A data structure used for fast access to rows in a table. An index is usually built for the primary key of each table and can then be used to quickly find a particular row. Indexes are also defined and built for other attributes when those attributes are frequently used in queries.
- Entity-relationship modeling
A technique used to describe the real-world data in terms of entities, attributes, and relationships. This is discussed in Appendix C.
- Normalized database
A correctly designed database that is created from an ER model. There are different types or levels of normalization, and a third-normal form database is generally regarded as being an acceptably designed relational database. We discuss normalization in Appendix C.