1. Northern College Diploma Philip Bird
Databases
Northern College Diploma
Philip Bird

2. What is a Database? Collection of all stored operational data
Uses schemas to
Separate the data from how its stored
Identifies entities and attributes
Limit access to approved applications/people
Include validation checks
Use 4th GL’s to allow easy querying
SELECT name, address FROM customer WHERE credit_limit>500

3. Each entity stores attributes that describes what we know about it
Database is composed of tables (entities) linked by key fields (Relational model)
Each entity stores attributes that describes what we know about it
These can be described by Bachman diagrams
Customer
(Cust_number, Name, Address, Credit_Limit)
0123 A.Wally 24 High Street 350
0234 S.Jones 12 Huddersfield Rd 600
Customer
Order
Stock Item
Supplier

4. Advantages Less data duplication New applications are easy to add
Easier security monitoring
Database can be distributed over many sites

5. Disadvantages Large and complex systems “All eggs in one basket”
Difficult to design (data modelling)
Requires management
“All eggs in one basket”

6. Other Issues Security Integrity Consistency and Concurrency Recovery
Administration