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 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.

Drawing Relationship Diagrams

Create a Relationship Diagram

In the repository for your application, right-click on
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.
Click Add New.
In the pop-up, enter its name.
PhixFlow opens a properties tab on the right, and a new relationship diagram on the left. The relationship diagram has a toolbar at the top; see the Toolbar section below for details.

When you make any changes to the diagram, remember to Save.

Open a Relationship Diagram

To open an existing relationship diagram:

either, in the repository, right-click on its name and select Display.
or, in the properties toolbar, click the .
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icon.

Create a New Stream

Drag the
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icon from the toolbar into the diagram.
In the pop-up, enter its name, for example "Customer" and click . PhixFlow opens a new Stream properties tab.
PhixFlow adds a box to represent the data stream, and opens the properties tab for it.
To add attributes to the stream
- either, in the properties tab on the right, In the Attributes section, click Add New.
- or right-click the stream and select Add New Stream Attribute.
PhixFlow opens a Stream Attributes properties tab where you can specify details for the attribute, such as its name, data type and length.
If this is the unique identifier, tick Primary Key. Remember to include ID or UID in the name.

Add an Existing Stream

In the repository, open the list of streams.
Drag a stream from the repository into the diagram. PhixFlow adds the stream with a list of all of its attributes.
If the stream has many attributes, click to collapse the stream so that it only shows the primary and foreign keys.

Connect Attributes

To connect attributes in different streams, click-drag from one attribute to another. PhixFlow shows the currently selected destination in bold. Release the click to connect to the selected destination.

PhixFlow can only connect primary and foreign keys. If you connect standard attributes, PhixFlow automatically sets them to be foreign keys.

You can change which attributes are the Primary Key or a Foreign Key using the tick boxes in the the Stream Attributes properties.

PhixFlow automatically sets the type of relationship according to the keys:

one to one: from primary key to primary key
one to many: from primary key to foreign key
many to one: from foreign key to primary key
many to many: from foreign key to foreign key.

Properties

For information about the properties toolbar, and about the sections Parent Details, Analysis Models, Description and Audit Summary, see Common Properties. We recommend you always add a Description that explains the purpose of the item you are creating.

For a full list of all the PhixFlow property tabs and windows, see Properties, Windows, Menus and Toolbars.

Basic Settings

Field	Description
Name	Enter the name for the entity-relationship diagram. When yo press Return or save a new properties tab, PhixFlow opens an empty diagram in the workspace on the left.

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.