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WJEC CG3.6

Topic 6: Databases and Distributed Systems

TermDefinition
Foreign key A foreign key is a primary key from one table; appearing in another table; used to form links between tables.
1NF no repeating groups of attributes.
Data warehouse A data warehouse is a large collection of data stored together logically for further processing. Examples: An insurance company might use data warehousing to check claims histories together with other insurance companies’ data to try to detect fraud.
Data mining Data mining is the analysis of a (large) amount of data in a data warehouse. Example: A supermarket might use data from a loyalty card scheme to send information to particular customers with special offers etc.
Primary key A primary key is a field which uniquely identifies a record in a database, for instance in a membership database membership-number might be used to uniquely identify each member.
3NF Third normal form means that data items are dependent on the whole key and nothing except the key (or the key, the whole key and nothing but the key).
Data duplication/redundancy (storing of the same data more than once) is likely to occur if a database is not normalised.
Flat File System? A flat file system may contain a number of single tables with no links between them, whereas a relational database normally contains a number of linked tables (/relations).
Why normalise a DB? data independence; reduces data duplication / redundancy; reduces the danger of inconsistency / improves data integrity; reduces the danger of data being lost during update.
Database administrator A database administrator is the person in a company who is responsible for the structure and management of the database system and the data in it.
Database Management System (security) The DMBS may allow certain users read and/or write access to certain records or fields only.
Why is an index often used by a database management system? An index is used to improve read access times to records, and also to sort the records for viewing.
Distributed database? Databases often contain huge amounts of data. It is often more efficient to store data on a number of different computers (probably in different locations) to maximise performance.
State two advantages of a relational database over a flat file system. Redundancy (data duplication) is reduced (therefore saving space); Risk of inconsistent data is reduced (better integrity of data); Data independence allows different views of the same data.
Created by: mcounsell