1.3.2 Databases

• consists of only a single file [1] • requires little expertise to maintain [1] • may have redundant data which can lead to increased storage requirements [1] • flat file database is harder to update so data might be inconsistent [1]

• a relational database is one that uses different tables for different entities • consists of linked tables [1] • maintains data integrity [1]

an item of interest about which information is stored

• a unique identifier for each record [1] • used to establish relationships between tables • can be used to fetch any record from a table

• the field/column which links two tables together [1] • it is the field/column that refers to the primary key in another table [1]

• specifying another attribute to be indexed for faster search [1] • an indexed field that is not unique • the index consumes additional storage space in the database [1]

• one -to one • one - to many • many to many

Each entity can only be linked to one other entity

One table can be associated with many other tables

Many tables can be associated with many other tables

• the process of coming up with the best possible layout for a relational database • normalisation tries to accomplish the following : • no redundancy so data integrity is maintained • consistent data throughout linked tables • records can be added and removed without issues • complex queries can be carried out

• all field names must be unique ( to avoid confusion about which record should be retrieved or updated) • values in fields must be from the same domain (e.g data type) • values in fields should be atomic so for every cell there must only be a single value • no two records can be identical • each table needs a primary key

this is because duplicate records take up unnecessary space and can cause inconsistencies if updates are not performed on all of them

• the data is already in 1NF • any partial dependencies have been removed • meaning no fields can depend on only part of a composite primary key • so each table should serve its own single purpose

• Means one of more fields depend on only part of the primary key • this issue can arise if the primary key is a composite key

• create a linking table • assign primary key from the 2 initial tables as the composite primary key for the new linking table • this flips the M:M relationship to become to 1:M relationships

• data is already in 2NF • any non-key dependencies are removed • all keys are dependant on the primary key, the whole primary key and nothing but the primary key

When the value of a field depends on the value of another field which is not the primary key

• creates a Data structure on specific fields/columns allowing the database engine to quickly locate and access relevant records during queries • primary key is automatically indexed • adding an index to a field speeds up searches on that field which would otherwise have to be searched sequentially

• allows faster search + data retrieval from the indexed field[1]

• consume additional storage space • for small tables, benefits of indexing may be negligible or even counter productive

Consists of 4 parts : - capturing data - selecting data - managing data - exchanging data

• paper based forms • OCR (optical character recognition) • OMR (optical mark recognition) • MICR (magnetic ink character recognition) • sensors • smart card readers • barcode scanners

• involves a human reading the form and manually typing the information into a computer based system • to avoid errors : • every part of the form must be labelled clearly • instructions to complete the form in black pen • instructions to complete the form in capital letters • use of tick boxes • squares for entering each letter separately