Example ERD
The following ERD shows the tables and attributes for a school.Key Concepts
| PhixFlow Relationship Diagram | Examples | ||
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A table represents a thing or entity.
| Entities:
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The table has a list of attributes. If you display the table data in a grid, the attributes will be the column headers. They name what the data is, and sets the type (date, integer, string etc.) and length of the data (100 characters, bigstring etc.) | Student attributes:
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PhixFlow automatically generates an attribute that is the unique identifier, UID. This is the table's primary key. The records for this attribute will all have a unique value.
| Primary Keys
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You can create a relationship between the primary key in one table, to an attribute in another table. On the diagram the relationship is shown as an arrow from a primary key to an attribute in another table. When you are designing screens, you can create views to display attributes from a table AND from tables with a direct relationship. Between two tables with multiple relationships, each connection must have a unique name. | By convention, set the name of a relationship an action (verb) that follows the left-right flow of the diagram.
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Relationships show that the data in a primary key in one table also appears in an attribute in another table. The attribute may have a different name, but it must represent the same data. This attribute is a foreign key. When you create a relationship in an ERD, PhixFlow automatically sets the foreign key status for the attribute. | Employee attributes:
Department attributes
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Understanding Relationships
Relationships From and To
Relationships between tables have a direction that depends on which table you are focused on. For example, the Teacher table shown below has two relationships.
- The school DepartmentID primary key connects Into the Teacher table. This is highlighted in blue.
- And the Teach table connects From its TeacherID primary key to an attribute in the Course table. This is highlighted in green.
One-to-many and Many-to-One
The arrow is always drawn from a primary key to another, non-primary, attribute. This represents a one-to-many relationship, for example, one teacher→ runs→ many courses.
For this type of relationship, PhixFlow automatically sets it to be aggregate. This means the relationship reports the total number. So a teacher runs 3 courses. In the ?? properties, you can clear the aggregate setting to report the full list of their courses.
A many-to-one relationship is implied when you read a relationship in the opposite direction. For example, a departhment has many teachers, and several teachers work for one department.
Finding out about the relationships between tables
- Use the ERD. You can highlight relationships From and To
- Use the properties?? Relationships are listed under From and To
Many-to-many
To create a many-to-many relationship, you need an intermediate table that has foreign key attributes from the tables you want to connect.
For example, there is a many-to-many relationship between customers and products.
- A customer → buys → many products
- A product → is bought by → many customers
The intermediate Customer Purchase Record table has both the CustomerID and ProductID as foreign keys.
- Customer purchase → records → CustomerIDs
- Customer purchase record → lists → ProductIDs
Finding out about the relationships between tables
- Use the ERD. You can highlight relationships From and To
- Use the properties?? Relationships are listed under From and To
Shift select
square select
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 in the Repository
When you create a relationship diagram, you start in the repository. Find the
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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.
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
Check its in PhixFlow the delete
| 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. |
| Ungroup | Select a grouped set of items and then click to ungroup them. Select several items then click to group them together. |
| Group | Group: Select several items then click to group them together. |
Back: ? | |
| Forward:? | |
| Align options | Click/hover to show all options for aligning items on the canvas |
| Align Grid | Organise selected items into a grid pattern. |
Align left | Align selected items to the left |
Align right | Align selected items to the right |
Align top | Align selected objects to the top |
Align bottom | Align selected objects to the bottom |
| Distribute horizontally | |
| Distribute vertically | |
| Table create: | Drag onto the canvas to create a table |
| Table list: | Click to list available tables |
| Save | Save the diagram. |
| Refresh | Redraw the diagram. |
| Help | Open the learning centre page for more details. |
| Properties | Open the properties for the selected item. |
Context Menu
| Currently | Change to | Tooltip? |
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| Configure Table | ?Table properties - use the properties icon?? | |
| Remove from Diagram | Remove from diagram | |
| Show all tables using this table | List tables with relationship into this one | Can this be list related tables with 2 panels??? |
| Show all related tables | List tables this relates out to | |
Permanently Delete → Delete (no undo) | Delete everywhere | ? mention no undo |
Video showing a worked examples
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Video script (4 mins)
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On entry, on creations...
Sketch out in Word
Incontext help design?
Title, video script, links....
Have a look at how the GUI is being affected by changes to ICONS
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