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Lesson 2Entities and their attributes
Objective Describe how entities become tables

Define Entities and Attributes in ERD Model

Step 1: The first step in the logical design stage of the (DBLC) database life cycle is to create a conceptual model. This involves converting business objects (and their characteristics) identified during requirements analysis into the language of entities and attributes for use in an ER diagram.

Attributes, Entites and the ERD Model

In an Entity-Relationship Diagram (ERD) model, the attributes of an entity represent the characteristics or properties of that entity. Entities are objects or concepts in the real world that have specific attributes. Attributes describe the qualities, characteristics, or properties of the entity, and provide a way to distinguish between different instances of the same entity. For example, if we have an entity named "Employee," its attributes could include name, address, date of birth, and employee ID number.
Attributes in an ERD model are represented as ovals connected to the entity with a line. The name of the attribute is written inside the oval, and the data type of the attribute is often specified outside the oval. Attributes can be categorized as either simple or composite. Simple attributes represent a single, atomic value, while composite attributes represent a collection of related simple attributes. For example, the address attribute of the "Employee" entity could be a composite attribute made up of street address, city, state, and zip code.
Attributes can also be categorized as either single-valued or multi-valued. Single-valued attributes have a single value associated with them, while multi-valued attributes can have multiple values associated with them. For example, the "Employee" entity might have a multi-valued attribute called "skills," which could include values like "programming," "project management," and "communication." In summary, the attributes of an entity in an ERD model represent the characteristics or properties of that entity, and provide a way to distinguish between different instances of the same entity. Attributes can be simple or composite, and single-valued or multi-valued.


An entity is a business object and can be either tangible (such as a person or an item) or intangible (such as an event or a reservation). Every entity in a database must have a different name. It is common practice (but not required) to name entities in the singular.
Step 2: Entities become tables in a database. Special types of entities, discussed in a later module, are sometimes created to represent the relationship between other entities.

Requirements analysis, Logical design, Physical design, Implementation, (Monitoring, modification, and maintenance)
A database consists of a PERSON entity and the table consists of the attributes of the PERSON

When thinking about what constitutes an entity, it is important not to confuse an aggregate concept, such as an inventory or a medical history, with a single entity. These aggregates actually represent groups of entities and not single, discrete entities.


Just as business objects have characteristics that describe them, entities are described by their attributes. When we represent an entity in a database, what we actually store are that entity’s attributes. In a nutshell, attributes store data values[1] that either 1) describe or 2) identify entities.

Attributes become fields in a table.

Attributes that describe a person (for instance, customer, employee, student, etc.) would include such things as name, address, and telephone number. Attributes that identify a person would include such things as social security number or any combination of letters and numbers that uniquely identify a person.
  1. Attributes that describe entities are called non-key attributes.
  2. Attributes that identify entities (entity identifiers) are called key attributes.

The next lesson explains the purpose of entity identifiers.

Entities Attributes - Exercise

Before moving on to the next lesson, click the Exercise link below to test your understanding of entities and attributes.
Entities Attributes - Exercise

[1]data value: Data entered at the intersection of a row (record) and column (field); the data describes or identifies the subject of the record.