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The Role of an ER Diagram in Data Modelling

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Entity relationship diagrams (ERD), aka ER diagrams, are structured flowcharts used in both modeling and debugging databases. In data modeling, ER diagrams are created to visually represent the concerned entities and the connective relationships between them.

The charts are generally created with simple symbols and geometric shapes such as lines, arrows, rectangles, rhombuses (diamonds), and ovals to organize, map, interconnect, and visualize the data. Depending on the project, its needs, and one’s choice of style, the list of shapes and symbols can be expanded.

The Role of an ER Diagram in Data Modelling

How to Create an ER Diagram?

To create an ER diagram for data modeling, we will need to first:

  • Identify all concerned entities within the database.
  • Identify how they relate to each other.
  • Create a flowchart that displays the entities and their interconnective relationships in clear, organized visualizations.

ERDs can be created manually, but that would not only waste time unnecessarily, manual ERDs also tend to be both erroneous and incomplete. Use an online ER diagram tool instead to easily draw even the most complex and comprehensive entity relationship diagrams for effective data modeling.

However, in case you are not completely familiar with the aforementioned concepts, such as entities, relationships, and flowcharts, then you might want to go through the following pointers as well.

What is an Entity in an Entity Relationship Diagram?

Entities in an ERD can be defined as the principal interconnected subjects that are relevant to the sector and the diagram’s goals. On the diagram, each entity will be represented as a major cluster of organized data about that specific entity, enclosed within a chosen geometric shape (rectangle, oval, etc.). For example, in a business ER diagram, Client, Customer, Order, Product, Supplier, etc., are the common entities, just as Teacher, Student, Guardian, Subject, Class, Lesson, etc., are often the primary entities in an ERD for schools.

What is a Relationship in an Entity Relationship Diagram?

Relationships are the interconnecting datasets that factually and visually join two or more entities together on the diagram. The relationship data is generally organized inside a rhombus or diamond shape with an illustrative headline. They are to be placed adequately between the various entities that they are connecting.

Just like entities, relationships also vary based on the ER diagram’s sector and goals. For example, the entities Teacher and Class could be connected by the relationship headlined Qualifications. In a business setting, the two entities, Supplier and Product, are often connected by the relationship Demand.

What is an Attribute in an Entity Relationship Diagram?

As you may have noticed, the meanings are quite literal when it comes to ERDs. Attributes can be values and qualities that are often used to characterize and categorize entities for further clarity. At the same time, attributes can also be a value and quality-based description of a relationship. In traditional flowcharts, attributes are generally encased in an oval shape, but there can be variations.

The Role of Colors in an ER Diagram

Color coding is very effective in delivering the intended information quickly and with better clarity. Although color coding is not mandatory by default, all new entity relationship diagrams should be color-coded unless specified otherwise. For example, assigning appropriate colors to the Client entities based on their respective importance/value is a common practice in related business relationship diagrams. Just be sure to add a small color index to the diagram that explains how you color-coded them.

What Roles do Symbols Play in an Entity Relationship Diagram?

Symbols play the same role as their name indicates; they symbolize the intended directions, connections, values, attributions, etc., of the relationships visualized on an ER diagram. For example, relationship lines visually connect the entities, while arrows indicate the order in which onlookers are supposed to follow the diagram. A relationship line that connects two entities and ends with a + symbol may indicate a positive relationship, while a line that ends in a – sign could be symbolic of a negative relationship.

Note that the same symbol may mean different things in different ER diagrams, as it depends entirely on the context. In an ERD that’s focused on data visualization to identify and eliminate unnecessary entities and relationships for a leaner business process, the + sign could show an entity that is adding more steps to the process, while the – sign could be indicative of a suggested alternative that can potentially decrease the number of steps. Therefore, any symbol you use while creating an ER diagram should have a precise and clear context that’s relevant to the diagram’s subject matter.

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