Databases
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define database
persistant organised (stored in records and fields) store of related data
define an entity
A real thing like people or customers (the table name in the database)
define a table
collection of data that relates to an entity (customers)
define a record
collection of data about one singular entity (rows)
define field
a unique piece of data about an entity i.e (student firstname) (collumns)
define a flat file database
a table with multiple entities i.e table with data on both customer and item that they buy
why is a flat file database bad
because everytime a customer buys an item all their data needs to be re added to the table so if address changed it has to be changed on every order
when would an intersection table be used
in a many to many database
define primary key
A field which has a unique value for every record A unque identifier
how does an intersection table work
uses the primary keys from the needed records in order to reference them i.e customer 3 bought procuct 17
define secondary key
a second unique identifier Not always present. film number (primary key) film name(secondary key)
define foreign key
primary key used in another table (intersection table?)
what is referential integrity
a given element that is referenced in another table is not deleted (not just records could be fields)
What does ACID stand for
atomicity consistency isolation durability
what does Atomicity mean (in ACID)
that a transaction is either entirely processed or not at all proccessed
What does consistency mean
That the transaction cannot break the pre-exsisting rules of the database i.e a string is not added in place of an integer
defin normalisation
a set or rules for a database to follow in order to be the most efficient
what level normalisation is flat file
Un normalised
what are the rules of first form normalisation
no collumns have repeating data (i.e maths,science) in one box data must be in its atomic form i.e first name surname must have a primary key
rules of second normal form
must be in first normal form first partial dependencies get split so any fields that only depend on one of the keys get split into a new table one primary key
rules of third normal form
all fields are fully dependent on the primary key non key dependencies are split i.e email is based of student name not subject
Why use an intersection table [3]
to change many to many relationships to make the database third normal form reduces data redundancies
1 pro and 1 con to having multiple keys [2]
pro , faster searching con, larger storage or insert, update and delete actions will take longer
Using an example, describe a scenario when a flat file database may be an appropriate solution. State an advantage of using a flat file instead of a relational database. [3]
when the data bse only contains one type of entity personal contacts list (only contains phone numbers) easier to use or import into another system