What is an Entity Relationship Diagram?
By Nipon Ekanarongpun
Entity Relationship diagram is simply a graphical concept which shows the flow of information
input and output. It is a conceptual data model intended to make use of E-R diagrams and mind
maps in order to communicate effectively within the system. Entity relationship diagram has
three main components, entity, attribute, and relationship.
Entity includes all information about things that are all combined to form a great collection
of information that will be useful in a developing system or any incomplete processes. Attributes
are components in a system that is mainly used in entity relationship diagrams to show
connections between larger information and smaller information.
For example, students are layered down and categorized into different attributes, gender
and age. One of the most important factors of entity relationship diagram is relationship. From
its name, it shows the relationship between information in the system by joining two entities
that are related.
Entity Relationship Diagrams Database
First, learning how the system works will help a lot in deciding on how the entity relationship
diagram will work. Knowing the system's processes and progress will help collect databases
and gather information, working sequences, and reports needed. In order to add the information
into the diagram, considering how much entities can be divided will make the system well-organized
and structured.
Though, the amount of entities might vary from each other depending on the
system as well as the amount of information input; entities in the system must include both
strong and weak entities. Specifications on relationships between entities should be well-considered.
Also, it is fairly important to plan on what attributes as well as which types should be connected
and related to the given entities so that information will be stored as much as possible. The
attributes though, must contain a key attribute or a main attribute for reference.
Entity
Entities in entity relationship diagrams are main factors that lead to further information.
Entities are things or objects that are combined to form a collection of information or data
used for developing systems. There are three main types of entities:
1. Visual entity (individual entity, place entity, object entity)
2. Concept entity
3. Existence dependency
An entity will be grouped in a rectangle; most entities are nouns that describe the system.
There are three main types of entities: strong, weak, and associate entity. Regular entity
or strong entity is independent from other entities while weak entity is interdependent. Composite
entity can convert M:M relationship, a complex type of relationship, into 1:M relationship
which is a lot easier to understand; a symbol for composite entity is a rhombus within a rectangle.
Attribute
An attribute is any information that specifies and defines given entities which can be
separated and divided into different groups. The quantity of attributes might vary from each
other depending on the system and how much information is needed in the system. Attributes
are presented in ellipses or ovals; nouns are mainly used as representations to make things
easier to understand. For example, attributes might include gender, age, employee codes, and
favorites broken down from an entity, employees.
Types of Attributes:
1. Simple attributes
2. Composite attributes
3. Key attributes
4. Single-valued
attributes
5. Multi- valued attributes
Simple attributes are attributes that cannot break down into other components. Composite
attributes are opposite of simple attributes which can be broken down into numbers of components
for example, name can be broken down into surname, middle-name, and first name. Key attributes
are attributes that show specific points of unique factors of a specific entity that will be
underlined in the E-R diagram.
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