4.3.6 Database Systems

Question 1

define: relational database

Answer 1

a group of tables linked together by primary and foreign keys

Question 2

define: primary key

Answer 2

a unique key used to identify record/table

Question 3

define: foreign key

Answer 3

a field of one table which is also the foreign key of another table

Question 4

define: normalisation

Answer 4

a staged mathematical process which removes repeated groups of data and incosistencies

Question 5

define: improvements

Answer 5

databases can be improved/made more efficient by adding tables to make the relationships one-to-many

Question 6

what are the security advantages of relational databases over flat file databases

Answer 6

-Hierarchy of passwords:
limits users to various parts of the program (1) A receptionist would only have access to basic customer details whilst a manager would see all information on the customer account. (1)

-Access rights to parts of the program :
only certain users can access and change the data (1) clerk would see all the information on a customer account but be unable to alter the hire rate details whilst a manager could. (1)

Question 7

what are the security and general advantages of relational databases over flat file databases? (RICI)

Answer 7

-data consistency:
Data consistency is the relationship between the input data, the processed data and the output data as well as other related data.(1) If the system is working properly the data will be correct at each stage and is said to be consistent.(1)

Data redundancy:
where you store an item of data more than once / A company may hold its data in different files.(1)
Data which is repeated unnecessarily is called redundant data.(1)

Data integrity:
Less chance of errors in data (1) as data only appears once in database (1)

Data independence: the data and the programs used to access it are separate,(1)
New systems can still use existing data. (1)

Question 8

what is a data warehouse? what are the advantages?

Answer 8

-a large collection of archived data used for decision making e.g allows the company to see who has bought what items and then target them with special offers

ADV:

• allows the organization to store information about every item/customer
• allows the organization to see who has done what (bought which items) and when
• can use it to plan future changes and developments in their system
• allows the organization to use data mining
• speeds up searching
• allows them to see most popular item and buy more to sell.

Question 9

what is data mining?

Answer 9

interrogating the data to find patterns in the data which is stored in the warehouse

e.g fighting shoplifting in clothes shops; Jaeger used DM to look at transactions and position of item in store and found even with tags most items stolen were near the doors, this led to increased CCTV and prosecutions.

Question 10

what is a distributed database?

Answer 10

A distributed database has data stored on a number of computers at different location but appears as one logical database

e.g a hotel chain might use a distributed databases to store details of reservations. each hotel store has its own reservation on a local computer

Question 11

what are the advantaged of a distributed database?

Answer 11

-if data is stored on the central site, it could b re-duplicated from local site
(sibs live in an apartment, mum lost her heater so we give her the heater she needs from our flats)
-if one server fails, the other servers can be used (that heater fails, so she comes to our flat to use our heater)
-allows sharing of data and the result of processing data
(she is now sharing our heater and the result is she is warmer)
-faster response to user queries of the database
(because shes at our flat if we ask how to do something she can show us straight away)

Question 12

what are the disadvantages of distributed database?

Answer 12

-Heavy reliance on network and communication lines which is not always reliable
(bc mum is using our heater all the time it doesn’t work as well)
-Software more complex than a centralised database system.
(we tried to fix her heater but its too complex for us)
-if data is stored and updated in more than one place there is an increased chance of data inconsistency.

Question 13

Normalisation question

Answer 13

Normalisation Questions:
Look at the question for clues on the other tables needed, usually says in the question. Make sure you:-
• Define the name of each table
• Define the foreign keys (a PK in another table)
• Define the primary keys
egg.
PATIENT (PatientID, surname, phone, WardID#, ConsultantID#)
CONSULTANT (ConsultantID, surname, phone, specialism)
• Underline = Primary Key
• # = Foreign Key