Explain the term data redundancy
Data redundancy is where you store an item of data more than once. A company may hold its data in differ files. This is wasteful because some data may need to be input twice and if data is changed in one it will need to be changed in the other.
Explain the term data consistency
Data consistency is the relationship between the input data, the processed data and the output data as well as other related data. If the system is working properly the data will be correct at each stage and is said to be consistent
Explain the term data integrity
Data integrity is the correctness of the data. Truthful, accuracy.
Explain the term data independence
Data independence is where the data and the applications/program’s used to access it are independent/separate.
New applications can be developed to access the data without changing the data./ new systems can still use existing data.
Describe what a data warehouse is?
(Large, archive, + used for decision making)
A database used to store an organisations historical data which is used by a MIS to extract information to help managers make decisions.
Explain what is meant by data mining?
(Trends, patterns or generating new information)
Data mining is the analysis of a large amount of data in a data warehouse to provide new information.
Explain what is meant by the term data normalisation
Normalisation is e process undertaken to ensure that a database has no redundant or inconsistent data.
Minimises duplication - allowing accurate processing of data and that the database has referential integrity.
Explain what is meant by a relational database
A large collection of data items and links between them structured in such a way that it allows it to be accessed by a number of different applications program’s.
A relational database is many databases or tables linked together by using primary and foreign keys as relationships.
What is a primary key?
A primary key is a field that is used to uniquely define a particular record or line/row in a table.
What is a foreign key?
A foreign key is a field of one table which is also the primary key of another. Foreign keys are used to establish relationships between tables.
Advantages of a distributed database
- Improved performance - quicker searches can be performed
- Less traffic on network if data is accessed on local database within the department
- Does not rely on one storage area
Disadvantages of distributed databases
- More complex to set up, maintain and install
- Security risk because data is stored at different locations
- If network server fails data cannot be accessed from all databases
- Chance that data gets inconsistent because a high number of staff at different locations have access to data
What is a DBMS?
A database management system is a method of managing the interface between the data stored and the program’s that uses the data.
What are the uses of DBMS?
- Allow a number of users to access the same data and create work such as searches, reports, updating and delete files.
- Ensure that data is secure and protected.
- Create access procedures - some users will have access to certain files. Some access will be ‘read only’ or ‘write only’
What is a database?
A database is an organised collection of related data.
What is a flat file database?
A flat file database is a simple database that stores all data in a single file or table.
Can be stored in a text file, spreadsheet or in a database file that contains one or more unrelated tables.
What are the problems with flat files?
- Data redundancy - large amounts of duplicated data, makes data entry slower, uses disk space/ memory, leads to other problems ….
- Reduced data integrity - more likely to be inaccurate, same data entered over and over - typing errors
- Difficult to update - if entries change then all instances have to be updated
- Security - all users have access to the same table/file/set of data
- Data dependence- user face (amongst other things) is tied to a specific file
Advantages of using a relational database?
- Avoids data duplication - data stored once and linked by key fields
- Controlled redundancy - minimises data duplication, no repeating attributes
- Ensures data consistency - to all users
- Data independence - data stored separately from program’s so can add new fields because data is independent of the application which uses it
- Increased security -
- password hierarchy - can create passwords to individual tables
- DBMS can vote permissions - read only, write only etc.
- data validation and verification techniques can be used
- data is stored separately from program’s so different program’s cannot overwrite data
- Data integrity - specify constraints on the data to ensure it is in the correct format and range
- Easy to add new applications - without affecting stored data
- Flexibility - data drawn from different files can be combined in different ways, producing better quality information
- Greater efficiency -
- data Inputted once - saves on time and human resources
- memory space is less - saves on computer resources
Disadvantages of relational databases
- Complex to set up and maintain
- Database software is large complex, expensive and requires powerful computers
- All applications which access the data will be affected if database fails
Advantages to the company of a data warehouse?
- can be mined
- it allows the company to store all the details of what it has sold to every customers
- the company can see who uses a loyalty card and exactly what they have bought and what method they used to pay for it
- can compare information like the sickness data from different stores
How might the company use data mining? (Example)
- comparison with competitors
- useful ‘what if’ results from modelling exercises
- predictions for future sales
- analysis of best sites for shops
Explain how the data warehouse and data mining could be useful to a mail order company
- the mail order company generates huge quantities of data
- stored in a consistent order
- to make interrogation more productive
(Data warehousing) - is interrogating the date
- investigates potential patterns
- returned information can be tested for plausibility
(Data mining)
Advantages of distributed database
- data used locally can be stored locally and network traffic kept to a minimum
- if data lost on central site it could be rue duplicated from local site
- allows sharing of the data and results of processing the data
- new locations can be added to the database without the need for rewriting the entire database
Disadvantages of distributed database
- software more complex than a centralised database system
- because data is transferred it presents more of a security risk by hackers
- as all the data is not stored in one location if local site does not have adequate backup then this data might be lost to others
