File-based and relational databases, keys and DBMS features
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The teaching part (1 min) is free to watch. A free account opens the whole lecture: 6 practice questions, 2 real past-paper questions with the answers explained, the mistakes that lose marks, the full-marks tip, a one-card summary and a quick quiz.
What this lecture covers
- One fact, stored once
- The file-based approach
- The relational approach
Read the transcript of the teaching part
Last time
Before we start: last time, in Artificial intelligence, copyright, software licences and ethics, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.
One fact, stored once
A shop keeps customers' addresses in the sales file, the delivery file and the invoice file. When a customer moves, someone must change all three, and if one is missed the shop posts to the wrong house. A relational database stores each fact once, and links tables with keys. A database management system looks after it all.
The file-based approach
In a file-based approach, each program has its own data files. The same data is often held in several files. That causes data redundancy, which wastes space, and inconsistency, when copies disagree. It is also hard to combine data from different files, and hard to control who can see what.
The relational approach
A relational database stores data in tables of rows, called records, and columns, called fields. Each fact is stored once. Tables are linked by keys, so data can be combined with queries. There is less redundancy, so the data is more consistent. Several users can share the data at once, and the DBMS controls access to each table.
How often it comes up
The whole chapter: Databases.
Chapter 8: Databases
- File-based and relational databases, keys and DBMS features 7 min
- Normalisation, E-R diagrams and SQL scripts 7 min
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