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

• minimises data duplication
• improves consistency
• eliminate insertion anomalies
• eliminate data redundancy
• eliminate update/deletion anomalies