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

Special terms on this page

Terms

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attribute

An attribute defines the characteristics of data.

In an Excel spreadsheet, data is often organised into columns, where the first row is the column header. For example, a spreadsheet of customer data may have column headers Name, Address, Postcode, Phone Number and the rows below contain the data, with each row being a data record. A table to represent customer data may have the attributes: Name, Address, Postcode, Phone Number. However, the attributes do not contain the data. Attributes contain the information about the data. For example, it includes the type of data, for example, whether it is:

text
a number
a date
a true/false field.

The range of characteristics available depend on the context in which the attribute is being used. For example, an attribute for the same data in a:

table includes expressions to control how its values will be processed.
view includes properties related to how it will be displayed in views, such a labels and alignment. You can even set attributes to be hidden, so although they are present in the table, they are not shown in views.
table-action specifies how a user interaction in an application can change the value of records in the table.

Overview

An ERD is an entity relationship diagram. Use an ERD to represent the information that your application will use and how it is connected. PhixFlow uses the connections between data when you come to make views. When you select something to add to a view, PhixFlow can offer all the connected tables and attributes. This means you can easily create views that combine data from different tables.

PhixFlow's ERDs are simplified Entity-Relationship Diagrams. The concepts are explained in this article: ER Diagram Tutorial in DBMS.

Sections on this page

todo better image Doc simple 1

Entities are the data tables that your application has or will have.

First create your "entities"

table, attributes

Set up relationships

e.g. invoice is for a customer. Tell PhixFlow "customer name" is connected via customer ID

This creates arelation and marks it as a forign key - with glyph to show it.

Its important to understand that the connection is there for other stuff - for creating views that combing information from multiple streams so that you can

If you wanted a screen with cust info at top and a list of depts it would need to know how to do this.

The line means go and find it from the other table and can then find the matching attribute and preport the records (by following the line). (show it as an animation

Turn this into a simple explanation with a sequence

Start with tables and attribures

Explain primary keys

Explain relations and foriegn keys.

Key concepts
Entity-Relationship Diagram	PhixFlow Relationship Diagram	Examples
A database table represents a thing or entity.	A table (was stream) represents a thing or entity. Choose a name that reflects the entity your table represents.	Entities: Company Employee Department Product
A database table has columns for different aspects of the data. The column headers are called data attributes.	The table in a relationship diagram has a list of attributes.	Employee attributes: EmployeeID Name Address Phone Department
	PhixFlow automatically generates a unique identifier, UID. (Integer, sequence) attribute that has unique values. The unique attribute is the primary key.	Primary Keys Employee stream: EmployeeID Department stream: DepartmentID
	Improve When the data from one stream's primary key also appears in a different stream, it is a foreign key. This gets set automatically when you connect up an ERD todo update using UX terminology Use an example to show that the things are linked by relationship and that the data is connected and may not have the same name (can be a later concept) Tell PhixFlow there is a relationship	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. Relationships can only be one-to-many, from primary key to foreign key. When you are designing screens, you can create views to display attributes from a table AND from tables with a direct relationship.	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, Between two tables with multiple relations, each connection must have a unique name.

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.

todo Update labels with UX terminology Departments needs to go and there is not foriegn key here...

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.

All of the plural foreign keys are wrong

Limitations - single hop relationships. You cannot go Project → Opportunity → Statuses at the moment. You need to go from one table

Project → Opportunity
Project → statuses

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 ERD 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.

todo Draft image needs improving

Related things

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

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, a view can display the data records for selected attributes using a Stream View. This can be a grid (table), a graph or a chart. If a table has no relationships to other tables, PhixFlow can only show attributes and records from that stream.

When a table has a direct relationship to other tables in a relationship diagram, PhixFlow can display the data for the attributes from the related tables.

For example, with the following relationship diagram, you can create a view based on the "Departement" stream that shows

Company name from table Company
Department names from table Department
Product category and Status from table Products

todo better diagram and example

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.