Example ERD

The following

example shows an ERD for a school. Each box represents a different table.

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Key Concepts

PhixFlow Relationship DiagramExamples

Term	Means	School Example
Table	A table represents a thing or entity. The table name is displayed in the blue area. Image Added Tip Choose a name that reflects the thing your table represents.

Entities

	Tables: School Department Class Room Teacher Course Student
Attributes	The table has a list of attributes. If you display the table data in a grid, the attributes

will be

are 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

any format details.  Image Added	Student table has attributes: StudentID Student Name Student Address Intake Year
Primary key	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. You may want to rename UID to something more descriptive, although it's a good idea to include ID in the name. Primary keys are indicated using a green key icon. Image Added Note We recommend that a primary key attribute is an integer, because PhixFlow can automatically generate a unique integer value for each new data record.	Primary

Keys

keys in different tables: DepartmentID ClassRoomID TeacherID
Relationship	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. Relationships always point from a primary key to a non-primary attribute. Image Added When you are designing screens, you can create views to display attributes from a table AND from

tables with a direct relationship

other, related tables. 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. a department→ has→ many teachers a teacher → runs→ several courses classroom → is ued by→ many courses
Foreign key	Relationships show that the data in a primary key in one table also appears in an attribute in another table.

The

The attribute may have a different name, but it must represent the same data. This attribute is a foreign key.  Foreign keys are indicated using a grid icon. Image Added When you create a relationship in an ERD, PhixFlow automatically sets the foreign key status for the attribute.

Employee attributes: EmployeeID (primary key) Name Address Phone Department = foreign key for DepartmentID Department attributes DepartmentID - primary key Department Name Purpose Department Manager = foreign key for EmployeeID

Understanding Relationships

Relationships From and To

Relationships between tables have a direction that depends on the table on which table you are focused on. For example, looking at the Teacher table, shown below has two , you can see 2 relationships.

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• The school DepartmentID primary key connects Into connect into the Teacher table. This inbound relationship is highlighted in blue.
• And the The Teach table connects From its connects from its TeacherID primary key to an attribute in the Course table. This outbound relationship 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  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

1. Use the ERD. You can highlight relationships From and To
2. 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

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Finding out about the relationships between tables

1. Use the ERD. You can highlight relationships From and To
2. 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.

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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.

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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

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, 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 

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todo better diagram and example

Check its in PhixFlow the delete

Select a grouped set of items and then click to ungroup them.

Select several items then click to group them together.

Back: ?

Align selected items to the left

Align selected items to the right

Align selected objects to the  top

Align selected objects to the bottom

Click to list available tables

Context Menu

Permanently Delete → Delete (no undo) 

Video showing a worked examples

scripts incontext

Icons

Video script (4 mins)

Bullet pointed list of where incontext

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

Close of play TUESDAY

inbound/outbound

Primary key

attribute

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