Tables and Attributes

The table name is displayed in the header.

The table has a list of attributes, which represent the different data you want to record. For example, the Teacher table records the Department, Address and Name of teachers.

You can see that the Address and Name attributes have the word "String" next to them. PhixFlow needs to know what type of data the attribute contains. To make it easy to create an attribute, PhixFlow sets the type to string by default. It is important that you change the attribute to reflect the nature of the your data. For example, an attribute of Telephone Number would be integershould be integer.

To see or change the data type for an attribute, click on it's name in the table to open it's properties panel on the right.

Relationships and Foreign Keys

Sometimes we want to have the same data in different tables. For example, both the Teacher and ClassRoom tables need to have the name of a department. The ERD represents these relationships using a line that joins the SchoolDept table to the ClassRoom table and to the Teacher table (screenshot below). 

When you create a relationship from a primary key to an attribute, PhixFlow automatically sets the attribute to be a foreign key.  Foreign keys can have different names to the UID, but they must have the same data type , for example integer with a precision of 10as they contain the same form of data. For example, the Department attribute has the same values as the UID values for the school department. However, in the ClassRoom or Teacher table there may be more than one instance of a value. For example, there may be 10 teachers who belong to the Maths Department.

The ERD's entities, attributes and relationships define the logical structure of the data that your application uses.

If you want to highlight the relationships that affect a table, click the table to select it. The following screenshot shows the Teacher table is selected.

• Blue lines indicate relationships to a foreign key in the selected table
• Green lines indicate relationships from the primary key in the selected table.

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Why Relationships are Important

In an application screen, you can add grids showing data from tables. However, there are attributes from a table that you do not want to include in a view, such as the UIDs, and there may be attributes in other tables that you do want to include in a view. For example, your application might want to show:

• Course Name
• Department Name
• Teacher Name
• Number of Students

PhixFlow's relational tables mean that you can show data from different tables using the relationships between primary and foreign keys. For example:

Course Table - 1 step to Teacher Table

1. Course via Teacher foreign key to Teacher Name

Course Table - 2 steps to Department Table

1. Course via Teacher foreign key to Teacher Table
2. Teacher Table via Department Foreign key to SchoolDept Table (and therefore department names).

the Maths Deparment UID would occur 10 times, once for each of the 10  maths teachers.

One-to-many and Many-to-one

PhixFlow always draws a relationship line from a primary key to foreign key. This represents a one-to-many relationship. The "many" end of the line has several lines ??add image. for For example, one teacher runs many courses.  A many-to-one relationship is implied when you read a relationship in the opposite direction. For example, a department has many teachers, and several teachers work for one department.

Many-to-many 

To create a many-to-many relationship, you need an intermediate table that has foreign key attributes from each of the tables you want to have a relationship. For example, many students take many courses. This A many-to-many relationship is shown below, using the intermediate table called CourseAttendee.

• A course is attended by many students
• A student takes many courses.

Why ERDs are Important

The ERD's tables, attributes and relationships define the logical structure of the data that your application uses.

However, a table has attributes that you may not want an application user to see, such as UIDs or audit data. When you are creating views to display data in your application, you may want to combine attributes from different table s into one view.  For example, your application might want to show:

• Course Name
• Department Name
• Teacher Name
• Number of Students

Each of these attributes comes from a different table. The relationships that you create between tables in an ERD make it possible for PhixFlow to create views using attributes from different tables. For example:

Course Table - 1 relationship to Teacher Table

1. Course.Teacher foreign key to Teacher table, and therefore Teacher.Name

Course Table - 2 relationships to Department Table

1. Course.Teacher foreign key to Teacher Table
2. Teacher.Department foreign key to SchoolDept Table and therefore SchoolDept.Name.

A Note About Data Records

An ERD defines the table, attribute and relationships. It does now not show any data records. If you think of an Excel spreadsheet, an ERD shows the name of the worksheet (table) and the titles of the columns (attributes) . An ERD also shows the data type and relationships. All this defines the logical data structure. The records themselves are not requiredbut not the rows of data.

You can draw :

• either define an ERD before adding any data to PhixFlow. In this case you create the tables, attributes and relationships
• or you can load data from external sources

• first. You can then drag tables into the ERD

• and simply add the relationships

• .

How to load data or add it to empty tables: link??

If your tables See:

• loading data page to do??
• Defining Data Structure using ERDs

If you are working with tables that have records, to see them:

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Jiras

?? Initial Cap only

Configure → Table properties

Hide Attributes - Hide attributes

Remove this item from the Diagram → Remove from ERD... model, screen, workflow, actionflow...

Permanently Delete → Delete everywhere

Inital cap only

1. Click on a table in the ERD to open its properties.
2. In the properties toolbar, click 

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   .
3. Select tbc

Context menu

To see the context menu for a table:

1. View Chart (this should be default view!??).
2. PhixFlow displays a grid showing all the data records.