Databases Flashcards
What does Referential Integrity mean?
Prevents you from deleting related records
What is a serial file?
Permanent storage of data
- Data is in the order at which it was entered
- No order to the data is maintained
What is a sequential file?
- Data stored in order of a key field
- The order is maintained when new records are added
What is an indexed sequential file?
Maintain an index to allow groups of records to be accessed quickly.
What is a database?
A database is a structured, persistent collection of data
What are the advantages of using a database?
- Makes processing more efficient
- Reduces storage requirements
- Avoid redundancy
- Allows different users to only see relevant data
What is a DBMS?
Software which manages the database
What features does a DBMS provide?
- A manipulation language to access and change the data
- Integrity to ensure efficiency and structure is not compromised
- Additional security
- An interface for other programs to access and use the data
- Programs/data independence
What are the components of a database?
- Tables that store data in rows and columns
- Queries to manipulate data
- Forms or user interface
- Reports
What is a flat file?
One table and all data is stored within it.
What are the disadvantages of a flat file?
- Inefficient as it is not easy to query
- Data is duplicated (redundancy) inefficient use of storage. Errors can occur between different records easily and integrity is compromised.
What is a relational database?
A relational database has more than one related table.
How do you get from a flat file to a relational database?
Normalisation
What must be true for a relational database?
- Each record must be unique, primary key is unique identifier for the record.
What is a foreign key?
A field in one table that uniquely identifiers a row of another table or the same table.
What are the types of relationship?
- One to One
- One to Many
- You cannot design a database with Many to Many relationships
What is the primary key also known as and what is it used for?
Index used to quickly find records.
What are secondary keys used for?
To quickly perform query’s on the database.
