A table, a log and a photo
A café has three kinds of data. A neat table of customers. A log file where the till writes each event. And hundreds of photos and reviews.
A computer can search the table in a blink. The log is harder. The photos are hardest. The shape of the data decides the work.
Key words
| Word | What it means | Example |
|---|---|---|
| Structured data | Data in a fixed layout of named fields, each with a set type. | A customer table |
| Semi-structured data | Data with some pattern, but a flexible layout. | A log file |
| Unstructured data | Data with no set layout or model. | Photos, reviews, audio |
| Field | One named column of a table, such as surname. | phone |
| Data type | The kind of value a field holds, such as a whole number or text. | integer |
| Relational database | A database that keeps data in linked tables. | Customers and orders |
| NoSQL | A kind of database that does not use fixed tables. | A store of reviews |
| Data warehouse | A large store of organised data kept for analysis. | Ten years of sales |
| JSON | Text in labelled pairs inside braces. | {"id": 12} |
| XML | Text in nested tags that name each piece. | <id>12</id> |
| Log file | A file where a system writes down what happened, line by line. | Till events |
The cells students fill in are left blank in this preview.
By the end of this lesson
Note
I can tell structured, semi-structured and unstructured data apart and say where each is used.
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.
The three shapes compared
| Shape | What it looks like | Where you meet it |
|---|---|---|
| Structured | Fixed field names, fixed type or length, organised, consistent | Spreadsheets, relational databases, data warehouses |
| Semi-structured | A flexible model | Some spreadsheets, log files, JSON and XML files |
| Unstructured | No set model, not organised in a set way | Social media, web pages, documents, audio and video, often kept in NoSQL databases |
The cells students fill in are left blank in this preview.
Try it: see all three shapes
table_row = ["Sam", "Room 12", 14]
log_line = "2026-03-02 10:15 ERROR till offline"
review = "Lovely cakes but the queue was long!"
print("Structured, 3 fixed fields:", table_row)
print("Semi-structured, split at spaces:", log_line.split(" "))
print("Unstructured, just words:", len(review.split(" ")), "words")
# Try it: change the review and press Run.
A spreadsheet can be two shapes
A spreadsheet appears in both the structured and the semi-structured row.
A tidy sheet with one header row and one type in each column is structured. A messy sheet with notes in the margin, merged cells and mixed values is semi-structured. The tool is the same. The layout decides.
A common mistake
Warning
Many people think unstructured data has no use. It has plenty. A review holds feelings a table never could. The catch is that it takes more work to turn into numbers.