Key concepts | ||||
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Entity-Relationship Diagram | PhixFlow Relationship Diagram | Examples | ||
A database table represents a thing or entity. | A stream represents a thing or entity.
| Entities:
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The column headers of a database table are the data attributes. | The stream attributes are the data attributes. | Employee attributes:
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A stream must include at least one attribute that has unique values. | Primary Keys
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When the data from one stream's primary key also appears in a different stream, it is a foreign key. | Employee attributes:
Department attributes
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Tables or attributes can have various relationships to each other
| 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. | Relationships
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Note |
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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 onrelationship diagram, you start in the repository. Find the
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section
below for details.,
remember toOpen 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
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Create a New Stream
Drag the
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In the pop-up, enter its name, for example "Customer" and clickAdd 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.
Tip |
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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
Basic Settings
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.
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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 | ||||
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| Zoom out to see more of the diagram, with smaller text. | ||||||||
| Zoom in to see a smaller area of the diagram, with larger text. | ||||||||
| 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. | ||||||||
| 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 the relationship diagram. | ||||||||
| Refresh the diagram, for example to show changes to an attributes Primary Key or Foreign Key properties. | ||||||||
| Opens this help page for relationship diagrams. |