Data tables are separate from the programs/functions that use them
EG the same table may have two or more different views: the delivery function can see customer name and address only; however the credit control function can see the customer income, credit history, and contact details
Changes in the structure of the data tables only affects those programs/ functions that are reliant on that part of the structure
EG the introduction of a new field to a table only needs changes made to the functions that will use the field and not to all the functions that use the table.
Process of breaking down complex data structures into simpler forms
(1NF) Removal of repeating fields
(2NF) Removal of composite keys/partial key dependencies
(3NF) Removal of non-key dependencies
Normalisation is the process for making the structure of a relational database more efficient by defining tables, fields, and relationships to minimise duplication of data and increase data consistency. Data integrity is assured by data validation specified in the data dictionary. Complex queries are also achieved using efficient relationships between tables.
Provide a diagrammatic representation of the structure of the data and shows the types of relationships within the database. The relationships include:
one to one (not common)
one to many (common)
many to many (not physically possible) better to have:
The Nature of a Client/Server Database System (P210)
Client Computer: A local workstation that just provides the user interface to request data queries/reports from the server
Server Computer : A remote computer where the processing is carried out to provide the query results/reports to the client computer. The server computer is more powerful than the client computer because it has to contain the whole RDBMS.
The advantages of a client/server database system
cost-effective: clients are cheaper than servers so this expensive resource is made available to a large user base
• data consistency is maintained as one copy of data is held on the server, rather than a copy held on each workstation
• communication between client & server is minimal as only requests/results are communicated, not entire databases
• Department specific report formats or queries can be held on workstations meaning less room is taken up on the server and they are less likely to be accessed by the wrong people.
The End Now do the exam questions! Do the exam questions!