This page is for data modellers or application designers. It explains how to use a relationship diagram to understand how your system's data is connected.

Overview

Use a relationship diagram to represent the information that your application will use and how it is connected. It is important to understand the connections between data when you start to create relational views, which display data from different streams.

Relationship diagrams do not show changes over time, responsibilities or processes. To represent this type of information, use a Workflow Diagram.

PhixFlow's relationship diagrams are simplified entity-relationship diagrams (ERD). An ERD is commonly used to show the relationships between database tables. If you are not familiar with ERDs for databases, the concepts are explained in this article: ER Diagram Tutorial in DBMS.

Sections on this page

Key concepts
Entity-Relationship Diagram	PhixFlow Relationship Diagram	Examples
A database table represents a thing or entity.	A stream represents a thing or entity. Choose a stream name that reflects the entity it represents.	Entities: Company Employee Department Product
The column headers of a database table are the data attributes.	The stream attributes are the data attributes.	Employee attributes: EmployeeID Name Address Phone Department
	A stream must include at least one attribute that has unique values. This is usually an identifier, so has ID or UID in the name. The unique attribute is the primary key.	Primary Keys Employee stream: EmployeeID Department stream: DepartmentID
	When the data from one stream's primary key also appears in a different stream, it is a foreign key.	Employee attributes: EmployeeID (primary key) Name Address Phone Department = DepartmentID - foreign key Department attributes DepartmentID - primary key Department Name Purpose Department Manager = foreign key
Tables or attributes can have various relationships to each other By convention, a relationship is expressed as an action (verb) that follows the left-right flow of the diagram.	Attributes can have relationships. On the diagram the relationship is shown as an arrow. The relationship must have a unique name. Relationships can only be one-to-many, from primary key to foreign key.	Relationships one company → employs → many employee one employee → manages → several departments one department → makes → many products

We recommend that a primary key attribute should be an integer, because PhixFlow can automatically generate a unique integer value for each new data record.

More About Relationships

The name for the relationship should reflect its direction. For example:

either company → employs → people
or people→ work for → company
but not company → work for → people

PhixFlow imposes no restrictions on the names for relationships, but it must be unique in the repository.

One to One Relationships

In a PhixFlow relationship diagram, it is not possible to create a one-to-one relationship.

Many-to-Many Relationships

You can show a many-to-many relationship by using an intermediate stream. This stream has attributes that are foreign keys from the two streams you want to connect, with a one-to-many relationship into the foreign keys. For example

A customer buys many products
And a product can be bought by many customers
The intermediate stream is a Customer Purchase Record, which has both the CustomerID and ProductID as foreign keys.

Example

In a relationship diagram, a stream and its attributes are displayed as a box. You can expand or collapse the box using the icon in the top left. PhixFlow shows all the attributes when the stream is expanded, and only the primary and foreign keys when it is collapsed.

The following diagram shows some relationships between streams that represent a company, its employees and departments, the products it makes and the customers who buy them.

The company "contains" many departments. An employee "works in" a department, and a department can have many team members. In this company, the department "makes" several products, which "ship to" many customers.

Relationship diagrams are useful because you can design relational views that use data from multiple streams. For example, you might want a view that shows the employee details by department. This will display data from the Employee stream and the Department stream. The relationship diagram shows these are connected by the DepartmentID attribute.

Relationship Diagrams in the Repository

When you create a relationship diagram, you start in the repository. Find the

Error rendering macro 'excerpt-include' : No link could be created for '_relationship_diagram'.

section, right-click and select

Add New.

As you draw the diagram, PhixFlow adds items to the repository:

a stream for each table; see
a stream attributes for each attribute. These are nested under the stream in the repository.
a relation for each relationship.

Draft image needs improving

Relationship Diagrams and Relational Views

Relationship diagrams underpin the ability to create views that combine data from different streams.

When you create a GUI screen for an application,an area can contain information from a stream, displayed as a Stream View. This can be a grid (table), a graph or a chart. PhixFlow can show data from different streams, where the streams have a connection in a relationship diagram.

Toolbar

Zoom Out	Zoom out to see more of the diagram, with smaller text.
Zoom In	Zoom in to see a smaller area of the diagram, with larger text.
Align to Grid	Organise selected objects in a grid.
Align Objects to Left	Align all selected objects left.
Align Objects to Right	Align all selected objects right.
Align Objects to Top	Align all selected objects to top.
Align to base	Align all selected objects to bottom.
Error rendering macro 'excerpt-include' : No link could be created for '_stream_add'.	Either drag into the diagram to add a stream or click to open the list of streams in the repository and drag a stream in from the repository list.
Save	Save the relationship diagram.
Refresh	Refresh the diagram, for example to show changes to an attributes Primary Key or Foreign Key properties.
Help	Opens this help page for relationship diagrams.

Understanding Relationship Diagrams