Entity

An entity is a high-level organizational unit in SQL Server databases. The term is used in at least a couple of different ways.

According to Microsoft TechNet SQL Server Glossary, “1. In Reporting Services, an entity is a logical collection of model items, including source fields, roles, folders, and expressions, presented in familiar business terms. 2. In Master Data Services, an entity is an object within a model. Each entity contains related members that are defined by attributes.”

Entity-Relationship Model

Many databases are built using an entity-relationship (ER) model. The ER model was initially developed by Peter Pin-Shan Chen of MIT in the 1970s.

In ER modeling, the structure for a database is portrayed as a diagram, called an entity relationship diagram. An ER diagram is similar to the flowchart of a sentence breaking it down into its syntactical units. Entities are created as a series of points, polygons, circles or ovals connected by lines. The relationships between points, polygons, circles or ovals is represented by a line. Furthermore, every ER diagram has a matching relational table, and every relational table has a matching ER diagram.

Entities can be thought of a special class of nouns, such as employees, departments, products or networks, for example. An entity is typically defined by reference to its properties, called attributes. Relationships, on the other hand, can be thought of as verbs reflecting a state or actions, such as the act of purchasing, being a member of a group or being a supervisor of a department. A relationship is often defined according to the number of entities associated with it, referred to as the degree of relat