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 interconnected.

TODO: Check for info in these links

• https://www.sisense.com/en-gb/glossary/entity-relationship-diagram/
• https://www.smartdraw.com/entity-relationship-diagram/
• https://www.guru99.com/er-diagram-tutorial-dbms.html

Overview

Use an relationship diagram to visualise how your system's information is connected. PhixFlow relationship diagrams are similar to simplified entity-releationship diagrams (ERDs).  In PhixFlow, entities are represented by streams and their attributes. You can use relationship diagrams to draw the relationships between existing streams, or you can create the diagram and, at the same time, create the streams it represents.

For example, a simple relationship diagram can represent a company and its employees. A company has attributes, such as a name, address, turnover. In a PhixFlow stream, a company must also have an attribute that identifies the company uniquely. A company also has employees. In a relationship diagram this looks like:

Company  → employs → People
UniqueID
Name
Address
Turnover

Relationships can work both ways, for example a person "works for" the company. The relationships are usually expressed as an action (verb) that follows the left-right flow of the diagram. For example:

• either company → employs → people
• or people→ workfor → company
• but not company → workfor→ people

The relationship connects identifiers in each stream. A unique identifier in a stream is it's primary key. It uniquely identifies the row (data record) in the stream. In some cases a unique attribute from one stream is represented in another stream - this is a foreign key . It uniquely identifies a row in a different stream.

For example Person has attributes

• Name
• Address
• Employer - this contains the unique identifier of the company and is therefore a foreign key.

Relationships can be

• 1-1: primary key to primary key
• 1-to-many: primary key to foreign key
• many-to-1: foreign key to primary key
• many-to-many: foreign key to foreign key.

PhixFlow imposes no restrictions on naming relationships, but the relationship name must be unique. We recommend that you use an action word that represents the relationship, avoiding "has" or "contains".

The components of a diagram:

• Each stream is displayed as a box 
• The box also lists all the attributes
• Primary keys and foreign keys are highlighted in green
• Relationships connect stream attribute primary and foreign keys.
• You can collapse a stream box to show only the attributes that are primary or foreign keys.  

TODO Invoice example 

• Invoice has the totals information.  has attributes: custID, total, date etc. 
• Parent object - there are many
• And it shows the invoice lines e.g. call breakdown  - these are not the data records for the invoice
• Children with their own attributes: invoice id - 
• Relationship is btwn ID field invoice - and the invoice id
• Receipt is an invoice - individual lines - info

To show the process flow of data, use a BPMN diagram

Other affected pages: repository, toolbars

Properties

Basic Settings

Drawing Entity-Relationship Diagrams

To create an ERD, in the application repository, right-click ERD and select . PhixFlow opens the properties for diagram, where you can add the name and a description for it. When you press Return or save a new properties tab, PhixFlow opens an empty diagram in the workspace on the left.

Adding Entities

To open an existing ERD:

• either, in the Repository, right-click the name and select Display.
• or, in the properties toolbar, click the ERD icon (TODO add).

Entities are represented by streams and their attributes.

To add an existing stream, from the repository, drag an existing stream into the diagram. PhixFlow adds the stream and all of its attributes.

To add a new stream.

1. from the toolbar, drag the stream icon (TODO add) into the diagram.
   
2. Enter a name for the new stream and click . PhixFlow opens a new Stream properties tab.
   
3. To add attributes to an entity/stream:
   either, in the stream properties → Attributes section toolbar, click 
   or, right-click the stream and select Add New Stream Attribute.
4. In the new attribute properties, enter details for the Stream Attributes.

As streams can contain many attributes, you can collapse the view to show only primary and foreign keys. TODO ADD screenshot

Adding Relationships

To add a relationship, click on one attribute and drag the mouse pointer to an attribute in another stream. PhixFlow extends a red arrow line. Stop dragging, or click on an attribute name to connect the two. PhixFlow displays an attribute in bold when it has focus.

When you create a relationship, PhixFlow:

• sets the origin attribute to be a Primary Key which must be unique.
• sets the destination attribute to be a Foreign Key
• creates a one-to-many relationship

The Primary Key and Foreign Key are properties of the Stream Attributes. (TODO ADD the new properties to attributes)

If both attributes are

primary keys, PhixFlow creates a one-to-one relationship.

foreigh keys, PhixFlow creates a many-to-many relationship.

If you connect two primary keys, PhixFlow creates a 1 to 1 relationship.

You cannot create a relationship between attributes if they are not a primary or foreign key. If you add a relationship between attributes, PhixFlow automatically sets them to be one of these.

ERDs and Relational Views

TODO - Add how ERDs and Relational vies interact.

TODO - Possibly bugs or possibly me...

• I ended up with 3 streams that did not appear until the diagram is saved - can I reproduce this
• relationship end points can be drawn a long way from the mouse. 
• I can untick keys and it keeps the relationship
• When entities are below each other PhixFlow gets confused.

Toolbar

TODO Same as Model Window Toolbar Icons

	Organise selected objects in a grid.
	Align all selected objects left.
	Align all selected objects right.
	Align all selected objects to top.
	Align all selected objects to bottom.
	Distribute all selected objects horizontally. Changed ICON TODO
	Distribute all selected objects vertically. Changed ICON TODO
	Drag into the diagram to add a stream, or click to open the list of streams in the repository
	Save TODO
	Refresh TODO
	Help TODO