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<p><b>Новая страница</b></p><div>== Understanding basic database terminology==<br />
<br />
<p>A database consists of tables and columns.</p><br />
<p>Database Design Terminology</p><br />
Logical/Relational<br />
Logical/Object-Oriented<br />
Physical Implementation<br />
Entity<br />
Class<br />
Table<br />
Attribute<br />
Attribute<br />
Column<br />
Instance<br />
Object<br />
Row<br />
<p>Entity: An entity maps something in the real world. For example, departments within an organization, employees, or sales.</p><br />
<p>Attribute: Represent information about an entity instance or an object. For example, the birth date or Social Security number of an employee.</p><br />
<p>Entities (classes) are implemented in the database as tables.</p><br />
<p>Attributes are implemented in the database as columns.</p><br />
<p>Instances (objects) are implemented in the database as rows.</p><br />
<p>A primary key uniquely identifies a specific instance of an entity.</p><br />
<p>No two instances of an entity can have the same primary key.</p><br />
<p>The values of all parts of the primary key must never be null.</p><br />
<p>The most common types of primary keys in relational databases are ID numbers.</p><br />
<p>Sometimes more than one attribute (or sets of attributes) can be used as a primary key.</p></div>Admin