Computing - Databases

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Database
A persistent organised store of related data on a computer system
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Persistent
It is stored in secondary storage so that it can be accessed later
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What does a database have to be able to do?
CRUD - create, retrieve, update, delete
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Serial File
A file of items stored as a series - one after another
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Sequential File
A serial file order (maybe based on an account number), lot faster to find data
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Indexed Sequential File
A sequential file that is accessed using an index, which is a separate file
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Flat File Database
Database consisting of one table. Easily be set up
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Field
A characteristic of something stored in a database
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Record
All of the data about one item in a database
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Entity
Something that we store data about in a database
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Attribute
A characteristic of an entity. It becomes a filed in a data table. An example is a surname, an invoice number or car colour
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Data Redundancy
The unnecessary repetition of data. Leads to complex processing problems and is inefficient
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Data Integrity
When data reflects reality - being as it should be/what is expected
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Validation
The process of checking data as it is input to ensure that it is reasonable. Does not prevent all errors, only detects any breaking of the rules
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Data Handling Software
Can be set up to reject any data that does not conform to specified rules
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Validation Check - Check Digit
Calculation is done. Common on account numbers and bar codes. Data is entered, calculation is repeated and if the same check digit is not generated, input is rejected
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Validation Check - Format Check
Data might have to conform to a particular pattern
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Validation Check - Length Check
Data must be within certain limits
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Validation Check - Lookup Check
Some fields might be looked up to see if they are from an allowed range. Postcodes are looked up to see if they exist.
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Validation Check - Presence Check
Ensure that all important information has been included
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Validation Check - Range Check
Number must fall within limits
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Validation Check - Type Check
Data type might be restricted, eg - surname might be restricted so that no numerals are accpeted
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Verification
Process of checking that data is true/correct. By human inspection or automated with barcodes, OCR, RFID, Magnetic strips or smart cards
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Data Model
Way in which a database is constructed. Examples are flat file, hierarchical and relational
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Relational Database
Stores data in tables. Each table contains data about one entity. A table is called a relation.
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Attributes
A characteristic of an entity. It becomes a field in a data table
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One to many
A relationship where one record in a table may have links to many records in another table
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Entity relationship diagram
A diagram that shows how different entities used in a database are connected
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Data type
Software needs to know how to handle the data. This choice affects what processing can be done.
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Field Size
No point in reserving more bytes for each field than are necessary
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Validation
Rules are set to filter out some types of mistakes
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Key Field
Choose at least one field to make a primary key
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Schema
Definition of a database. Includes table structures and rules that will be followed
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Data dictionary
The stored schema of a database
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Primary Key
Has to be a unique value. Often used to link a table to a foreign key in a different table
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Database software needs to...
protect data from damage and unauthorised access, make sure all who needs it can get to it, supply users with no more than they need to work with
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DBMS
Database management systems. Software handles data directly and provides an interface to the apps. Separates application programs from the data.
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External user view
User friendly face that users of the database can see
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Conceptual (logical) View
For the database designer. Shows how the components are constructed and fitted together.
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Internal (physical) view
The stored data is, of course a stream of bytes
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Concurrency
Hundreds of people could be looking at a database at one time (availability to many). To avoid problems - record locking mechanism, when one user is looking at a record, no one else can change it but they can look at it. Prevents conflicting updates.
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ACID
Set of rules that protects a database from errors during a transaction
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Atomicity
Makes sure transaction is either completely carried out or not at all
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Consistency
Transaction must take the database from one valid state to another
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Isolation
No transaction may interfere with any other transaction
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Durability
Once a transaction has been committed, it must remain so
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Queries
Objects that extract data from a database. Used to select fields required and the conditions that need to be met
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SQL
Structured Query Language
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Reports
Printed output of data from the database
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Data mining
Is using a software to trawl through data from many sources, looking for connections.
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Other cards in this set

Card 2

Front

It is stored in secondary storage so that it can be accessed later

Back

Persistent

Card 3

Front

CRUD - create, retrieve, update, delete

Back

Preview of the back of card 3

Card 4

Front

A file of items stored as a series - one after another

Back

Preview of the back of card 4

Card 5

Front

A serial file order (maybe based on an account number), lot faster to find data

Back

Preview of the back of card 5
View more cards

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