Computing: Databases

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Define a database
A persistent organised store of data on a computer system
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Why do businesses need databases?
In order to operate properly. Businesses could not function without them.
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Databases should be..
accurate, up to date, available to those who need them, protected from those who should not have access
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Database administrators go to great lengths in order to protect their data against:
errors, loss, insufficient data, inconsistencies, unauthorised access
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How could data be lost?
A catastrophe, such as a fire or flood, an accident, such as an employee deleting data, malicious action.
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Errors in databases can result in:
Embarressment, such as sending bills to customer who have died. Financial loss, such as if a bank account is wrongly credited or debited. Life or death situations, such as incorrect navigational data for an aircraft.
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To avoid database problems, data is protected by:
Making regular backups, having a mirror database server so that data is saved in at least two places, storing backups in a safe place such as the cloud, restricting access, keeping audit trails of who has accessed data.
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What does data integrity mean?
The data reflects reality. The accuracy and consistency of data stored in a database.
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How can data integrity be maximised?
Suitable validation, software that prevents inconsistent states
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Explain the term 'validation'
The process of checking data when it is input. Carried out by software not humans. It checks the data conforms to certain rules.
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Explain the term 'verification'
The process of checking that the data entered is correct. It can be a simple visual check against the source data or an algorithm checks two copies, entered independently, and flags up inconsistencies
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Define the term 'redundancy'
the storing of the same data in multiple locations. An example of data redundancy is saving the same file five times to five different disks.
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What do databases make data easy to?
Access, search, sort, group, copy and protect.
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What is a view?
A subset of the data in a database.
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What does CRUD stand for?
Create, read, update and delete.
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What is data matching?
Compares different databases to look for paticular relationships . For example, it can be used to compare housing benefit claims with credit agency data in order to uncover benefit fraud.
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What is data mining?
Process that looks in many different unrelated databases. it may show up unexpected relationships that may not have been noticed before. An example is using a supermarket card data to look for connections between purchases and lifestyle indicators.
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What is a model?
A model is a data structure that attempts to represent reality in such a way that is useful to the owner of the database.
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What is the simplest model?
A flat file database. This is just rows and columns such as would be suitable for an address book.
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What is a row called in a database?
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What is a column called in a database?
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Why are flat file databases limited?
Data might be repeated unnecessarily, such as the names of cities in an address book. This would be data redundancy.
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What is a hierarchical database?
Linking items that are related to an item. Like a diagram.
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What is a relational database?
Store data in seperate tables. The tables are linked together so that related data can easily be extracted.
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What is a DBMS?
A database management system is a piece of software that looks after a database at a fundamental level. It acts as a go between connecting applications to the underlying data.
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What does a DBMS allow database administrators to do?
Create database applications, protect data, run queries to extract data, keep data consistent and keep data accurate.
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Why is it important to separate the applications from the data?
Programmers do not have to worry that their applications might damage existing data structures, new applications can be written without restructuring the data, data can be more easily shared between applications, data remains consistent.
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What is a transaction?
When a change takes place in a database. Transactions must not damage the integrity of a database.
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What happens if two users try to modify data at the same time in a multi-user database?
One of the transactions will fail.
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What is record locking?
It means that when a user has opened a record for writing, other users can only view it until the transaction is committed. Then it is unlocked for other users.
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What is a table?
Structures where data is stored
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What does a primary key do?
Uniquely identifies a record, can be one field usually a reference of some sort or a combination of fields
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The primary key of one table can be linked to..
the foreign key of another table.
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What does the designer need to do when setting up a field?
Choose what data type it will be.
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What is a form and what does it provide?
Data can be inputted into tables from forms or selected data can be output to the screen in a form. Forms have objects, such as buttons and drop-down lists, to make them easier to use. They provide a friendly user interface.
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What is a report?
An output from a database, which can be set up to summarise, group and select data.
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What is a graph?
A way some DBMSs use to simply call upon applications programmers to display data rather than having to write their own display routines.
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What is a Query?
A tool to extract a subset of data in the database. They can combine data from more than one table and present data in whatever order is required. A query will always include the 'FROM' command to identify the source of the fields.
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What is an example of a query?
SELECT "room_number","room_type","view","bath" FROM "tblRoom" WHERE "view" = TRUE AND "bath" = TRUE
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How can queries be created?
By a graphical user interface that lets the user assemble the fields and conditions required for a query. They use the mouse to click and drag. This is an easier way for a beginner at databases and queries.
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What is an additional, more technical way to create queries?
SQL (Structured Query Language) is used by writing code which checks the conditions before selecting data to display.
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What is a module?
A unit of software that takes care of some particular functionality of a database.
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What other features do DBMS's have?
Referential integrity: changes must not be made that are logically impossible, validation, security: read and write priveliges can be assigned to different tables for different groups and automatic backup: some DMBSs save transactions=preventdataloss
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Why do businesses need databases?



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Databases should be..


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How could data be lost?


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