The gym that texts the wrong people
A small gym has 8 names on its member list. The owner sends a text: "Half price this month!"
Two people get it twice. One person left the gym two years ago and is angry. One number is wrong, so a stranger gets the text.
Nobody looked after the list. How much work would it take? Is it worth it?
Key words
| Word | What it means | Example |
|---|---|---|
| Maintain | Keep data correct, up to date and useful over time. | Fix a phone number. |
| Out of date | Data that was true once but is not true now. | A member who left |
| Duplicate | A second copy of the same record. | Sam Patel twice |
| Archive | Move old data to a safe place. You do not use it every day. | Members from 2022 |
| Skills | What a person knows how to do. | Writing a short program to check the list |
| Record | One row of data about one thing. | Sam Patel and his phone number |
| Cost | The money it takes. Time and skills also cost money. | £20 an hour of staff time |
| Six Vs | Six words that start with V. They say what data is like. Volume is how much. Velocity is how fast. Variety is how mixed. Variability is how it changes. Veracity is how true. Value is how useful. | Velocity: new members every minute |
| Priority | What you do first because it matters most. | Fix wrong phone numbers first. |
The cells students fill in are left blank in this preview.
Data does not look after itself
People move. Phone numbers change. Members leave. A list that was right in January is wrong by June.
To maintain data means to keep it correct, up to date and useful. It is work that never ends.
Quick check: looking after data
Have a go
Quick check: looking after data
3 questionsYour answers are marked here and are not kept. A college account keeps every student’s marks.
Three things limit the work
Time: somebody must spend hours checking, fixing and deleting. Data comes in all the time, so the work comes all the time.
Skills: somebody must know how to do it. A person who cannot write a small program must find duplicates by hand.
Cost: time and skills cost money. Storage and tools cost money too.
Worked example: what does a check cost?
| Step | Working | Answer |
|---|---|---|
| Hours for one check | 3 hours | 3 hours |
| Checks in a year | 1 every month | 12 checks |
| Hours in a year | 3 x 12 (3 times 12) | 36 hours |
| Cost of one hour | The pay for a worker | £20 |
| Cost in a year | 36 x £20 (36 times 20) | £720 |
The cells students fill in are left blank in this preview.
Try it: find out of date records
members = [
["Sam Patel", "2026-09-28"],
["Aisha Khan", "2026-10-02"],
["Leo Brown", "2024-11-14"],
["Mia Evans", "2026-09-30"],
["Tom Hughes", "2023-06-19"],
]
# Members whose last visit was before the start of 2025.
# A date written year-month-day can be compared as text.
for member in members:
if member[1] < "2025-01-01":
print(member[0], member[1])
# Change the date to "2026-01-01" and press Run again.
How it all fits together
You have met three groups of ideas.
The six Vs say what your data is like: big, fast, mixed, changing, true or useful. The quality checks are ways to test that data is good. They say what you can do about it. Time, skills and cost say what you can afford.
A good decision uses all three.