Databae Systems Flashcards
What is a database?
A collection of data items and links between them, structured in a way that allows it to be accessed.
What is an entity?
A person, place or thing about which data can be collected
What is a record?
Is all the data about one thing made up of fields
What is an attribute?
Describes the characteristics of an object
What is a primary key?
A filed within a database which enables every record to be uniquely indenifited
What is a forgien key?
A key field in a different table that is used to link tables together
What is a composite key?
Consists of more than one attribute to uniquely identify an entity
What is referential integrity?
Ensures that the data in one table does not contradict the data in another table
What is a flat file database?
A simple database that stores all data in a single table. Useful for simple lists. Difficult to update, reduced data integrity
What is a relational database?
A more complex database that allows data to be stored across a number of tables. The tables are linked using relationships. Allows data to be retrieved from a number of tables using queries. It has improved data consistency, better security and reduce redundancy
What is data redundancy?
Storing data multiple times in multiple locations
What is data inconsistency?
Condtradictory data about an entity being held in a different location.
What is data integrity?
The accuracy and correctness of data.
What is a logical data model?
Produced during the design stage and is independent of database softwares. Identifies the entities and relationships between them.
What is a physical data model?
Produced during the implementation stage and defines the physical structure of the database. Creates the table structures and the keys for each table with validation rules
What is the purpose of normalisation?
To reduce data redundancy which will ensure that the data model is more efficient and will take up less storage space.
What is a data dictionary?
A file containing descriptions of the structure of data stored. Contains filed names, filed size, default values and table names.
What is an ER diagram?
A graphical representation and is a logical part of the data model. It identifies the entities, the relationships and the attributes for each entity.
Compare and contrast er and normalisation
-both uses at the design stage
-both identify entities and relationships
-normalisation follows a set of decomposition rules and er modelling is a graphical approach
