Databases

• What is a relational database?

  Data is held in more than one table
• What does an entity represent in a database?

  An object in the real world
• What is an attribute in the context of a database?

  A characteristic that describes an entity
• What are instances in a database?

  A set of values corresponding to an entity
• What is a primary key?

  An attribute that uniquely identifies each instance
• What is a composite primary key?

  A combination of primary keys used together
• What is a foreign key?

  A set of attributes referring to another table's primary key
• What is the standard notation for defining an entity in a database?

  • Entity_Name (Entity_Identifier, attribute_1, attribute_2, ...)
  • Names should be singular (e.g., student)
• What are the types of relationships shown in entity relationship diagrams?

  • One-to-one
  • One-to-Many
  • Many-to-Many
• How would you represent a student entity with attributes in standard notation?

  Student (Student_ID, Name, Age)
• How do entity relationship diagrams help in database design?

  They show the relationship between attributes
• What is the purpose of producing entity relationship diagrams?

  To represent a data model and entity descriptions
• What is the first step in producing a data model from given data requirements?

  Identify multiple entities in the scenario
• What is the goal of normalisation in databases?

  To reduce data duplication
• Why are databases normalised?

  To improve data integrity
• What are the key features of 1st Normal Form?

  • Each record has a primary key
  • Data is atomic (cannot be split)
  • No repeating groups of attributes
• What defines 2nd Normal Form in database design?

  • No partial dependencies
  • Applies when a composite key is used
• What is the requirement for 3rd Normal Form?

  • No non-key dependencies
  • All attributes depend only on the primary key
• What does the term 'dependency' mean in database design?

  An element relies on another for functionality
• What does 'atomic' mean in the context of database attributes?

  An attribute can't be sensibly divided
• If a name attribute is split into first and last names, what does this violate?

  1st Normal Form
• How does 3rd Normal Form differ from 2nd Normal Form?

  3rd Normal Form eliminates non-key dependencies