Databases

Question 1

characteristics of serial files

Answer 1

• data is stored in the order in which it was entered
• no order to the data is maintained
• useful for storing transactional data and initialisation files

Question 2

what are files

Answer 2

permanent storage of data

Question 3

alternative to a series file

Answer 3

sequential file

Question 4

characteristics of a sequential file

Answer 4

• stores data in order of key field
• this order is maintained when new records are added
• useful for storing master files
• index sequential files allow groups of records to be accessed quickly

Question 5

advantages of databases

Answer 5

• makes processing more efficient
• reduces storage requirements
• avoids redundancy
• allows different users to only see relevant dat

Question 6

what is the data management system

Answer 6

• an additional layer of software which provides
  
  • manipulation language to access and change the data
• integrity to ensure efficiency and structure is not compromised
• additional security
• an interface for other programs to access and use the data
• program/ data independence

Question 7

examples of DMBs

Answer 7

oracle

Question 8

what is a flat file database

Answer 8

allows the user to specify data attributes for only one table at a time, storing those attributes independently, there is no link between the different files

Question 9

what are relational databases

Answer 9

allows the user to specify information about multiple tables and the relationship between those tables

Question 10

what is a primary key

Answer 10

• a field which identifies the table
• has to be unique and has to exist

Question 11

what is normalisation

Answer 11

the concept of splitting up tables in a database and arranging the data tk move it from first to second to third normal form

Question 12

how to get a database into first normal form

Answer 12

• eliminate duplicate columns
• get rid of any groups of repeating data
• identify the primary key
• separate any attributes which are not atomic into separate attributes

Question 13

what is a composite key

Answer 13

a combination of two or more columns in a table that can be used to uniquely identify each row in the table

• uniqueness is only guaranteed when the columns are combined

Question 14

how to get a database into second normal form

Answer 14

• check that data is already in 1NF
• remove any partial dependencies
• fix any many to many rls

Question 15

what is a partial dependency

Answer 15

means that one or more of the attributes depends on only part of the primary key
- this can only occur when the primary key is a composite key

Question 16

what should we do if we find a partial dependency

Answer 16

split the table on that attribute and move it to a separate table

Question 17

what are the issues with a many to many relationship

Answer 17

Without proper normalization, many-to-many relationships can lead to data redundancy and inconsistencies.

Question 18

how to solve the many to many relationship issue

Answer 18

create a linking table

Question 19

how to get database into third normal form

Answer 19

• check data is in second normal form
• check there are no non key dependencies

Question 20

what is a non key dependency

Answer 20

where the value of an attribute is determined by an attribute which is not part of the key

Question 21

aim of normalisation

Answer 21

to make a databse more efficient by removing redundant/repetitive data