Flashcards
Databases
Flashcards do conjunto (18)
- 1DatabaseA persistent (permanent), organised (stored according to a structure) store of related data
- 2EntityAn object in the real world with data that needs to be stored
- 3RecordAn instance of an entity in a database
- 4AttributeA characteristic of an entity
Represented as a field in a database - 5TableA collection of data about a single entity
- 6FieldA unique piece of data about an entity
- 7Database Management System (DBMS)An application that interacts with databases, separating the database from the applications using the database
- 8Types of database1. Flat-file
2. Relational - 9Flat-file databaseConsists of a single file about a particular set of data
Will only represent one type of entity - 10Relational databaseA database containing a separate table for each entity in the system
- 11Keys in a relational database1. Primary Key - A unique identifier for each entity in a table; usually the first field
2. Secondary Key - A different identifier used for fast searching (e.g. film title for a database in a streaming service)
3. Foreign key - A primary key from another table; used to denote relationships between entities
4. Composite key - A primary key consisting of two or more attributes - 12Types of relationship between entities1. One-to-one
2. One-to-many
3. Many-to-many - 13Explain referential integrityAny changes made are made to the entire database
e.g. cannot delete a record without deleting other records referencing that record - 14IndexingIn order to search a database quickly, an index of primary keys is kept
The index stores primary keys in - 15Explain what is meant by normalisationA process used to produce the optimum structure of a database
- 16Features of a normalised database1. No data is unnecessarily duplicated
2. Data is consistent throughout the database - should be a consequence of no duplication
3. The structure of each table allows any number of items to be entered
4. Users should be able to make complex queries concerning data from different tables - 17Stages of normalisation1. 1st normal form (1NF)
-No repeating attributes
-No groups of attributes
2. 2nd normal form (2NF)
- In 1NF
- Contains no partial dependencies (can only happen with composite keys)
3. 3rd normal form (3NF)
- In 2NF
- Contains no non-key dependencies - 18Advantages of normalisation1. No data redundancy
2. Easy to modify
3. Fast to sort and search
4. Enforces referential integrity
Informações
- Descrição
- A level OCR A level Computer Science (Topic 4 - Exchanging Data) FlashCards sobre Databases, criado por James Norman em 28-01-2020.
- Criado por
- James Norman
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