A picture settles it
Two analysts argue about how customers, shops and products link. One says a product belongs to a shop. The other says it belongs to a customer.
Then somebody draws it. Boxes, arrows and words on the arrows. In a minute everyone agrees what the data looks like. Drawing a model is a skill you will use often.
Key words
| Word | What it means | Example |
|---|---|---|
| Hierarchical model | A tree: every item has one parent. | Folders |
| Network model | Items linked any way, so an item can have several parents. | Customers and shops |
| Relational model | Data in tables joined by keys. | Products and shops |
| Block | A box that stands for one kind of item. | Shop |
| Arrow | A line with a head that shows a link and its direction. | Shop to Product |
| Label | A word on a block or an arrow that names it. | stocks |
| Table | Rows and columns of data about one kind of item. | Products |
| Row | One record in a table. | P1, Notebook, S1 |
| Column | One field, down all rows of a table. | Kind |
| Key | A column whose value identifies a row or points to another table. | Shop id |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can draw three kinds of data model of the same data.
Starter: what you already know
Have a go
Starter: what you already know
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Drawing a hierarchical model
Use blocks for item types and arrows from parent to child. Put a label on each arrow.
Start with the root at the top. Every other block has exactly one arrow coming in. If a block needs two arrows in, it is not a hierarchy.
Check: read the tree
Have a go
Check: read the tree
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.