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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.  


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Key concepts
Entity-Relationship DiagramPhixFlow Relationship DiagramExamples
A database table represents a thing or entity.

A stream represents a thing or entity.

Tip

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

Tip

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


Note

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

in the Repository

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 

relationship diagram, you start in the repository. Find the 

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.Click  Insert excerpt_add_addnopaneltrue.
  • 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. TipWhen you make any changes to the diagram

    ,

    remember to  Insert excerpt_save_savenopaneltrue.

    Open a Relationship Diagram

    To open an existing relationship diagram:

    either, in the repository,

    right-click

    on its name or, in the properties toolbar, click the .

    and select 

    Display.

    Insert excerpt

    _relationship_diagram

    _relationship

    _

    diagramnopaneltrue icon.

    Create a New Stream

    Drag the  Insert excerpt_streams_

    add

    _streams

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     icon from the toolbar into the diagram

    .

    In the pop-up, enter its name, for example "Customer" and click Insert excerpt_dialog_finish_dialog_finishnopaneltrue. 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 streameither, in the properties tab on the right, In the Attributes section, click  Insert excerpt_add_addnopaneltrue.
  • 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

    1. In the repository, open the list of streams.
    2. Drag a stream from the repository into the diagram. PhixFlow adds the stream with a list of all of its attributes.
    3. If the stream has many attributes, click Image Removed 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.

    Tip

    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

    Insert excerpt_standard_settings_standard_settingsnopaneltrue

    Basic Settings

    FieldDescriptionNameEnter 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.

    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.


    Image Added

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    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 
    Anchor
    toolbar
    toolbar

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    _zoom_out
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    nopaneltrue
    		Zoom out to see more of the diagram, with smaller text.
    Insert excerpt
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    		Zoom in to see a smaller area of the diagram, with larger text.
    Insert excerpt
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    Organise selected objects in a grid.

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    Align all selected objects left.

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    Align all selected objects right.

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    Align all selected objects to top.

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    Align all selected objects to bottom.

    Insert excerpt
    _stream_add
    _stream_add
    nopaneltrue
    		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.
    Insert excerpt
    _save
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    		Save the relationship diagram.
    Insert excerpt
    _refresh
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    		Refresh the diagram, for example to show changes to an attributes Primary Key or Foreign Key properties.
    Insert excerpt
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    		Opens this help page for relationship diagrams.