Overview

PhixFlow ERDs define the logical structure of the data in your application. 

The following example shows an ERD for a school. A school has entities, for example: departments, teachers, students, classrooms and so on. All these entities are represented as tables. The lines connecting the Tables show tables show the Relationships relationships between them.

Table

This is an illustration of the elements which make up a Table in an ERDThe following illustration shows how an ERD represents a table.

The table has a list of attributes, which represent the different pieces of data you want to record.

Attributes are configured with a data type and associated properties; see Understanding Data Types. For example the Address attributes attribute is a string String which has an associated length; see Understanding Data Types. To change the attribute to reflect the nature of your data, click on the attribute's name to open it's properties, here you can and edit its details including the data typeproperties. 

It is important to set the correct data type and properties before loading records into a table, as you cannot change the data type once the table contains records. If you do have data and want to change the type you will need to add a new attribute or clear your data; see Clearing and Loading Data in an ERD.

You can create tables in an ERD manually, but if you already have data, PhixFlow can automatically create tables from it; see Adding Content to an ERD.

Primary Keys and UIDs

PhixFlow expects every table to have a special attribute called a primary key, which uniquely identifies each record. For example, teachers have a UID as the primary key. This is because they can have the same first or family name, or even both, so these attributes cannot be a primary key. When you create a table, PhixFlow adds an attribute called UID (short for Unique IDentifier) and configures it as follows:

• as the table's  primary key.
• as an integer.
• to automatically create a unique number for every record in a table.

This means PhixFlow can ensure all the UIDs have unique values. 

Display Name 

Anchor
display-name display-name

Typically a Primary primary key is not user-friendly and you do not want to display it. Instead, you want to display something that makes more suitable for sense to a humanperson. For this reason, when you create a table, PhixFlow automatically adds an attribute called Name and ticks the its Display Name property. The Display Name will be shown display name is shown in place of the Primary Key primary key when displayed on a Viewview or screen. Display Names names do not need to be unique and should be something user-friendly.

Lets Let's look at the following example:The . For the SchoolDept table is created and , PhixFlow has created both :

• a UID, for example 1490

• .
• a Name, for example Mathematics.

To help users make sense of this PhixFlow will display the department's Name, when when any relational When any view makes reference to the SchoolDept using it's primary key, PhixFlow displays the department name, not its number; see Using Relational Views. The configuration is shown below:

    SchoolDept                         SchoolDept 
    primary key  Primary Key                        Display Name 

Relationships and Foreign

Keys 

Anchor
relationships relationships

Tables in PhixFlow are relational, which means information in one table can be related to, or linked to, information to information in another table. The key benefit is you can access data in many different tables without needing to duplicate datait.

A foreign key is an attribute in one table, that refers to the primary key in another table.

In an ERD you can connect tables by drawing a line, called a relationship between them. For example, the Teacher table needs to have the name of a department. The ERD below represents shows this relationships relationship using a line that joins tables: the SchoolDept.DeptID to the Teacher.Department:.

When you create screens that show data, PhixFlow uses the relationships from defined in the ERD to provide options for displaying data from related attributes in the same grid, form, card, graph or chart; see Understanding Displaying Data (Views). This means we you only need to store the School DeptID against a teacher , but we have access to to be able to access all of the SchoolDept details such as Name.

When you create a relationship from a primary key to an attribute, PhixFlow automatically sets the attribute to be a foreign key. Foreign keys must have the same same data type  and and properties as the corresponding Primary Keyprimary key. For example, in the illustration above, the Teacher.Department attribute contains the same Data Type data type as SchoolDept.DeptID; see Understanding Data Types.

The foreign key represents the many side and the primary key the one side. This means that SchoolDept.DeptID is unique, there is only one record containing this unique information. The Teacher.Department, can have one or more instances of a value of DeptID. For example, the Maths Department UID could occur 10 times, once for each of the 10 maths teachers.

One-to-many and Many-to-one

PhixFlow draws a relationship line between a primary key and a foreign key. This represents a 1:many relationship. The "many" end of the line has several lines one-to-many relationship. For example, one teacher runs many courses.  A many:1 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

: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. A many-to-many relationship is shown below, using the intermediate table called CourseAttendee. Notice that CourseAttendee does not need a unique identifier.

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

Viewing ERD

Data 

Anchor
view view

Using ERDs in Views

PhixFlow displays data to application users via Views, most commonly views most commonly a grid view which , which displays data in table rows and columns. For more information on this topic see 

More Information

• Using Relational Views

Creating PhixFlow Tables From Existing Data

• Displaying Data (Views)
• Creating a Grid