22 min read
Duplicated Data
When the same fact is stored in more than one place, copies can disagree.
The Same Fact in Many Places
Sophie changes her phone number. She tells Amelia at the desk. Amelia updates the membership card: 07700 900 999.
A week later a copy of Northern Light is late. Oliver wants to call Sophie.
George still has the old number in a notebook in the drawer. Oliver still has the old number in a spreadsheet on the staff computer. Amelia also wrote the new number in the staff WhatsApp group, then the chat moved on.
Three copies. Two of them are wrong.
| Sophie’s phone in three places | ||
|---|---|---|
Why Duplication Hurts
The library already has data. It already stores it. It stores it in too many places, with no agreement about which copy is official.
George is not careless. He is busy. Oliver opened the spreadsheet on a Monday and has not opened it since. The WhatsApp group is not a register.
When the same fact lives in three places, staff cannot tell which version to trust.
One change, three stores
One official copy versus several private copies
| Several copies | One official copy |
|---|---|
| Update the card, forget the notebook | Update once; everyone reads that place |
| George and Oliver disagree on the phone number | There is one number to read |
| A WhatsApp message gets buried | The fact stays in the store on purpose |
Practice
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Oliver closes the notebook. “We cannot keep doing this,” he says. “The library is growing. We need one place that holds the facts, and we need that place to be the one we all use.”
The next section of the course names that place: a database.
Section check
Before you continue: data
You have met raw data, information, why we store facts, and the cost of duplicated copies at Riverside Public Library. Try these without pressure — use hints if you need them.
This is practice, not the final assessment. Use hints. Look up a lesson if you are unsure — there is no score.
Self-check
Self-check
Self-check
Self-check
More lessons in Database Fundamentals · Next: What is a Database? · Previous: Storing Data