ICT WJEC A2 - TOPIC 6: DATABASE SYSTEMS

• RELATIONAL DATABASE: a group of tables linked together by primary and foreign keys
• PRIMARY KEY: a unique identifier for a record
• FOREIGN KEY: used to link to the primary key in another table
• DATA NORMALISATION: a staged, mathematical process which removes repeated groups of data and inconsistencies
• DATA CONSISTENCY- when data is held in more than one file it should be stored in a consistent way
• DATA INDEPENDENCE-the data and the applications (software) used to access it are seperate
• DATA INTEGRITY- the correctness of the data
• DATA REDUNDANCY- unnecessary duplication of the data
• DATA WAREHOUSE: a large collection of archived data used for decision making
• DATA MINING: interrogating the data to find patterns in the data which is stored in the warehouse
• DISTRIBUTED DATABASE:  has data stored on a number of computers at differnet locations but appears as one logical database

Data warehouse :

Advantages for a company:

• allows the company to store all the details of what has been sold to every customer
• can compare information (eg. sickness data) from different stores
• storing all this historic data makes the managers more prepared to make their decisions

Advantages for a library:

• allows the council to store information about every book
• allows the council to see who has borrowed books and when
• speeds up searching at the local library
• allows the library to find the most popular book and buy more

Example of how a company might use it: (point and expand)

eg. allows the company to see who has bought what items and then target them with special offers

Example of how a company might use it: (point and expand)

• fighting shoplifting in clothing stores- Jaeger used data mining to look at transactions and the position of the item in the store, they found that items near the doors were stolen more (with or without tags on them) they then decided to put more CCTV and more prosecutions

Example of how library staff might use it: (point and expand)

• librarians can gather information about the lending habits of individual members, and then use this information to change its opening hours so that the members can come to the library at times which are more convenient for them

Advantages of relational databases over flat file:

• HIERARCHY OF PASSWORDS (security): limits users to various parts of the program (eg. a receptionist would only have access to basic customer details whilst a manager would see all the information in the customer's account)
• ACCESS RIGHTS (security): to parts of the program only certain users can access and change data (eg. a clerk would see all the information on the customer account but they would not be able to alter the hire rate- whereas the manager could)
• CONSISTENCY OF DATA: this is using one file to hold a central pool of data (eg. a company may hold all it's customer data in one file. This avoids the need to input the data twice in different places- if the data is changed in one file, you wouldn't have to change it in the other)
• DATA REDUNDANCY: where data is stored more than once (eg. a company may store the same data in different files- this is wasteful as it takes time to do the same task more than once)
• DATA INDEPENDENCE: the data and the application used are seperate (eg. new systems being able to use the existing data)

ADVANTAGES:

• If data is lost on central site it could be replicated from the local site
• Allows the sharing of data and the results of processing the data
• Faster response to user queries of the database
• Easy to back up and copy data from one server to another
• If one server fails then other servers can be used

DISADVANTAGES:

• Software is more complex than a centralised database system
• If data is transferred then it presents more of a security risk from hacker
• if data is stored and updated in many places then this increases the chance of data inconsistency
• heavy reliance on networks and communications which may not always be reliable
• security issues with personal data being transferred

SECURITY ISSUES THAT APPLY TO DISTRIBUTED DATABASES AND METHODS TO OVERCOME THESE:

• computers are located on a number of sites, therefore it is important that only authorised users can access the system- this can be achieved by using passwords (and regularly updating the passwords)... ensuring that only the authorised users know what these passwords are

• data regularly transmitted between different sites, so the data may become corrupt or tampered with during transmission- checks are put in place to ensure that the data arrives secure and accurate (anothe method thta could be used is encryption)