Diagram updates, Change IntakeYear to Date
The table has a list of attributes, which represent the different data you want to record. For example, in the the Student table in the ERD above has the attributes: UID, Address, IntakeYear and Name.
Attributes are configured with a data type and associated properties, for example the Name and Address attributes are labelled as "String". To make it easy to create an attribute, PhixFlow sets the type to String by default. To change the attribute to reflect the nature of your data, click on the attribute name to open it's properties, where you can set the type. For example, IntakeYear is set to Date. 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.
| Tip |
|---|
If you have data outside of PhixFlow, we recommend you use a PhixFlow analysis model to connect to your data source(s) and use them to create your table structure; see Load Data. This means PhixFlow can create tables and can determine the data type for the attributes. |
This documentation refers to a specific attribute using the form table.attribute, for example: Teacher.Name, Student.Name or SchoolDept.Name. Ask if this notation or other notation is being used in the product - order or how would you do it in an expression...
Primary Keys and UIDs
PhixFlow expects every table to have a special attribute, called it's primary key. The primary key contains a unique value for every record. For example, several teachers 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 automatically adds an attribute called UID (short for Unique IDentifier) and configures it:
- as the table's
primary key.
If you look at the School ERD example above, you can see that every table has an attribute called UID, and that it has the primary key icon next to it. - as an integer; see the UID properties on the right.
- to automatically create a unique number for every record in a table.
This means PhixFlow can ensure all its own UIDs have unique values.
| Insert excerpt | ||||||
|---|---|---|---|---|---|---|
|
Relationships and Foreign Keys
Sometimes we want to have the same data in multiple places, but only update it in one location.... (to show the value). feels a little vague and doesn't do justice to the value of the relationships 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).
You are not just adding a line to a picture - you are creating a relationship that PhixFlow can use data from the other table...
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 primary key, not sure that needs to be said? but they must have the same data type and properties. For example, in the illustration above the Department attribute on the Teacher table has the same values as the contains UID values that correspond to UID values in the SchoolDept table. However, in the ClassRoom or Teacher table there may be more than one instance of a value. For example, the Maths Department UID could occur 10 times, once for each of the 10 maths teachers.
Usually, you want to use the foreign key attribute name, rather than UID, when the data is shown in a view. PhixFlow automatically ticks the Display Name property for a foreign key, as shown in the properties screenshot on the right.
Display name is used in a view....
I don't think the prev. para is correct - ticking the Display Name box on an attribute means that this attribute should be displayed in place of the foreign key attribute on a related table. In the example here you would set DisplayName=true for SchoolDept.name so that a view of Teacher joined to SchoolDept would show SchoolDept.name (a meaningful string) in place of Teacher.Department (a meaningless id). Note that this isn't implemented yet, so right now setting DisplayName does nothing.
One-to-many and Many-to-one
PhixFlow always draws a relationship line from a primary key to foreign key. This makes little sense unless the line has an obvious direction, and now that we're using the crow's foot notation there is no obvious direction. This represents a one-to-many relationship. The "many" end of the line has several lines. 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.
Come back and add something after doing relational views and aggregation: Gary says: This doesn't really explain why one-to-many / many-to-one are important. You might want to include worked examples showing the data you will get if you build a view starting with Teacher and a similar view starting with SchoolDept. You should also cover the importance of the 'Primary' table (the starting table in a joined view, in particular that you will only be able to edit fields that came from the Primary table, and only then if you haven't followed a one-to-many relationship.
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. 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.
Show in a relational view with worked examples in a table e.g using data in tables Sketch something up and use mockaroo and powerpoint for images: Again, I think this would benefit from a worked example showing that you get records with combinations of records from each table.
Why ERDs are Important
The ERD's tables, attributes and relationships define the logical structure of the data that your application uses.
Just that it relates to views and views talk about how you access them - keep this simple - show an example with real data....
However, a table has attributes that you may not want an application user to see, such as UIDs or audit data. How does this sentence relate to ERDs? 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:
Check annotation
This is done via a view picker.
Course Table - 1 relationship to Teacher Table
- Course.Teacher to Teacher.UID and display name Teacher.Name
Course Table - 2 relationships to Department Table (Tech check: this is true??)
- Course.Teacher to Teacher.UID
- Teacher.Department to SchoolDept.UID to SchoolDept.Name.
I feel this is too technical an example, where would a user see/ use this annotation? Should we show an example in an application or something more visual with the descriptions?
A Note About Records
An ERD defines the table, attributes and relationships. You can:
Creating PhixFlow Tables From Existing Data
You can create tables in an ERD, but this is time consuming. If you already have data, PhixFlow can create tables from it.
| Starting Point | Easiest Method | See | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| I have no data | Define the tables, attributes and their relationships in the ERD. You will need to add records to the tables. | Defining Data Structures using ERDs ??How | ||||||||
| I have data in Excel files | Drag the Excel files directly into an ERD. PhixFlow loads the data and adds the table to the ERD. In the ERD, you then add the relationships between tables. | ??Link to doc on XD flow 4.10 | ||||||||
| I have data but it's not in PhixFlow | First use an analysis model to connect to your data. PhixFlow can read the data structures to create tables. When you run analysis on the model, PhixFlow loads the data records. | Load Data | ||||||||
| I have data in PhixFlow already | In the ERD toolbar, click the
| Defining Data Structures using ERDs |
If you are working with tables that have records, to see the records:
- In the ERD, click on a table to open its properties.
- In the properties toolbar, click
.Select View ChartInsert excerpt _more_options _more_options nopanel true - Select
.Insert excerpt _view_show _view_show nopanel true - PhixFlow displays a the default grid view, listing all the data records.