From a story to a picture
A librarian tells you: "We have members and books. A member can borrow many books over time, and a book is borrowed many times."
From that story you can draw the plan of the system. This lesson gives you steps to do it, and a way to read someone else's plan.
Key words
| Word | What it means |
|---|---|
| Entity relationship diagram | a picture of the tables in a database and how they link, called an ERD |
| Entity | a thing we keep facts about, drawn as a box |
| Attribute | one fact about an entity, listed inside the box |
| Primary key | the field that gives every record its own unique id; underline it |
| Foreign key | a field that points at a record in another table; put a star after it |
| Cardinality | how many records link on each side: one or many |
| Link table | an extra table that turns a many-to-many link into two one-to-many links |
| Database | an organised store of tables that you can ask questions |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can read an ERD, and draw or complete one from a description, with keys marked and cardinality shown.
Starter
Have a go
Starter
3 questionsHave a go: your answers are marked here and then forgotten. Sign in if you would like your score kept, and to pick up where you left off.Sign in to keep your score
Your answers are marked here and are not kept. A college account keeps every student’s marks.
Read the diagram
Have a go
Read the diagram
5 questionsHave a go: your answers are marked here and then forgotten. Sign in if you would like your score kept, and to pick up where you left off.Sign in to keep your score
Your answers are marked here and are not kept. A college account keeps every student’s marks.