1.3.2 Databases

• Flat file- a simple database, consisting of information about a single entity.
• Entity- A category of an object, person, event or thing of interest about which data needs to be recorded.
• Primary key: something that uniquely identifies a particular record in a relational database.
• A second primary key in a database is called a composite key.
• Secondary key- An additional/alternate key, which can be use in addition to the primary key to locate specific data.
• Relationships between entities:

  One-to-one

  One-to-many (or many-to-one)

  Many-to-many
• In terms of a relational databases, data is held in tables (called relations) and the data has a primary key and a foreign key.
• Normalisation: a process used to come up with the best possible design for a relational database.
• Normalisation accomplishes:

  -No redundancy (unnecessary duplicates)

  -Consistent data throughout linked tables

  -Records that can be added and removed without issues

  -Complex queries that can be carried out
• 1st Normal Form: There must be no attribute that contains more than a single value.
• 2nd Normal Form: Database must be in 1NF

  No partial dependencies (no attribute is dependent on only a portion of the primary key)

  Should be functionally dependent on the candidate key.
• Flat-file vrs Relational database:

  • Flat-files may have redundant data whereas Relational database will not
  • Flat-files are harder to update
  • Relational databases are easier to change the format
  • Flat-file doesn't need specialist knowledge to operate
  • Relational databases provide security features
• 3rd Normal Form: Fields must be dependent on the primary/composite key (no trasitive dependencies)
• Relational databases- a database which creates different tables for different entities.
• Indexing- a method used to store the position of each record ordered by a certain attribute. Used to look up and access data quickly through an indexed primary and secondary key.