Where does the laptop live?
An IT team tracks laptops, rooms and the staff who use them. One laptop is in one room. But one member of staff may use laptops in three rooms, and one room has many staff.
How you link these things changes how fast you can answer a question. There are three common ways to organise the links.
By the end of this lesson
Note
I can describe three ways of organising linked data and say when each is best.
Key words
| Word | What it means | Example |
|---|---|---|
| Data model | A way of organising data and the links between items. | Relational |
| Hierarchical model | Items in a tree, each with one parent. | Folders |
| Network model | Items linked in any direction, so an item can have several parents. | Staff linked to many rooms |
| Relational model | Data in tables, linked by shared key values. | Assets and rooms tables |
| Key | A value that identifies a row. | R1 |
| Efficiency | How little time and space a job uses. | A fast lookup |
| Complexity | How hard something is to build and understand. | Many linked tables |
The cells students fill in are left blank in this preview.
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.
Three data models
A data model says how data and its links are organised.
The hierarchical model is a tree. Each item has one parent. Folders work this way.
The network model allows any item to link to any other, so an item can have several parents.
The relational model keeps data in tables. A key in one table points to a row in another.
Worked example: assets and rooms
| Model | How it holds the same data | Easy question | Hard question |
|---|---|---|---|
| Hierarchical | Room, then the assets under it | What is in Lab 1? | Where is every laptop? |
| Network | Assets, rooms and staff linked both ways | Who uses laptops in two rooms? | A new question with no ready link |
| Relational | An assets table and a rooms table joined by room id | Almost any question | Nothing is very hard, but it is more work to set up |
The cells students fill in are left blank in this preview.
Check: which model?
Have a go
Check: which model?
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.