This article will help you understand the Entity Relationship Diagram (ERD) generated from your data model. An ERD is a visual representation of the relationships between different tables in your database. It's a powerful way to see how your data is structured and how different pieces of information connect.

What is an Entity Relationship Diagram?

An Entity Relationship Diagram illustrates the logical structure of a database. It's composed of entities, attributes, and relationships.

Entities

An entity represents a "thing" or object in your data model that can be uniquely identified. These are stored as tables in our Databases, and are represented by rectangles in our Entity Relationship Diagrams. Examples of entities might include "Employees," "Performance Reviews," or "Applications."

Attributes

Attributes are the properties or characteristics of an entity, and are stored as columns in the table. For instance, the "Employees" entity might have attributes like "Employee ID", "Age", "Salary Band", and "Job Title." In the diagram, attributes are listed within the entity rectangle.

Relationships

Relationships define how entities are connected to each other. They indicate how data from one entity relates to data in another. For example, an "Employee" might have many "Performance Review," or a "Requisition" might contain many "Applicants." Relationships are represented by lines connecting entities, with symbols indicating the type of relationship.

How to generate your ERD

To Generate your ERD within One Model, go to Admin -> Admin Reports, and select Download next to the Entity Relationship Diagram:

The file will be automatically downloaded to your desktop.

How to Read Your ERD

When you view your ERD, here's a general guide to interpreting it:

1. Identify Entities: Look for the rectangles. Each one represents a key component of your data model.
2. Examine Attributes: Inside each rectangle, you'll see the specific data points associated with that entity.
3. Trace Relationships: Follow the lines connecting the entities. The symbols at the ends of these lines indicate the cardinality (one-to-one, one-to-many, many-to-many) of the relationship.

Types of Relationships

There are three primary types of relationships you'll see in our ERDs:

• One-to-One (1:1): Each instance of Entity A is associated with exactly one instance of Entity B, and vice-versa.
• One-to-Many (1:N): One instance of Entity A can be associated with multiple instances of Entity B, but each instance of Entity B is associated with only one instance of Entity A.
• Many-to-Many (N:M): Multiple instances of Entity A can be associated with multiple instances of Entity B, and vice-versa.

Common Symbols and Notations

Here's a quick reference for Some common symbols that may appear in your Entity Relationship Diagram:

Symbol	Found On	Meaning	Common Usage
	Relationships	One and only one	Link to a Dimension
	Relationships	Zero or one	These are rarely used within One Model
	Relationships	One or many	Classifying an Employee as multiple nodes in a single Dimension, such as Ethnicity (see Model below)
	Relationships	Zero or many	Link to a Fact Table
	Entities	Fact	A Fact Table that contains Metrics, such as the Employee Fact Table
	Entities	Dimension	A Dimension that is used to classify groups within Metrics, such as the Job Family Dimension
	Entities	Model	A table that is not used for Metrics or a Dimension, but may create a bridge between the two. An example is cases where an employee might be classified as multiple thing in a Dimension (e.g. ethnicity), and a Model table can be used to create that One to Many relationship
	Entities	Slowly Changing Dimension	A Dimension that changes over time, such as the Supervisor Dimension
	Entities	Geospatial Dimension	A Dimension that contains Latitudes and Longitudes for a Geomap - usually used on the Location Dimension
	Entities	Time Dimension	A Dimension that classifies time, such as the Timeperiods or Pay Periods Dimensions