What Is A Entity Relationship Diagram?
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 best ai porn 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.
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.
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. From its name, sing-valued attribute, it is an attribute that carries single information and uses the same symbol as simple property. Educational degrees and certificates is an example of a multi-valued attribute which can be broken down into numbers of components and is opposite of single-valued attributes. Multi-valued attributes are presented in double lined ellipses. It is very important to group the attributes correctly and relate them to proper entities, if the attributes do not match then there is a need for relationship to connect two entities so that attributes will relate to each other indirectly.
A relationship is simply a relationship between entities in a system. Like described in the above paragraph, a relationship is something that connects entities together and build up a relationship between the two. It also connects attributes in relation to another indirectly by using verbs.
Types of Relationships in E-R diagrams
1. One to one relationship
2. One-to-many relationship
3. Many-to-many relationship
One to one relationship shows a relationship of one of the factors in one entity in to another single entity. An employee wants a car, is an example of one to one relationship between a car and an employee connected by the verb ‘want’. One-to-many relationship is simply a relationship that extends from a single factor in one entity to numbers of other factors in another entity. A student wants high heels, sneakers, and boots, is an example of a one-to-many relationship. Many-to-many relationship, from its name, is a relationship between several numbers of entities. For instance, three students need to register numbers of subjects such as English, Thai, and Economics. Three students are numbers of entities, the numbers of subjects, English, Thai, and Economics is another entity while register is a relationship between the two. Relationships can be important for scheduling and data collecting; date and time can be included in relationships when it is needed for the system such as date of purchase and price.