ch13

Question 1

User-defined data type

Answer 1

a data type based on an existing data type or other data types that have been defined by a programmer

Question 2

Describe the purpose of a user-defined data type

Answer 2

To create a new data type (from existing data types). and to allow data types not available in a programming language to be
constructed

Question 3

Non-composite data type

Answer 3

a data type that does not reference any other data types.

Question 4

Enumerated data type

Answer 4

a non-composite data type defined by a given list of all possible values that has an implied order //// A (user-defined non-composite) data type with an ordered list of possible values

Question 5

Pointer data type

Answer 5

a non-composite datatype that uses the memory address of where the data is stored //// A user-defined non-composite data type used to reference a memory location

Question 6

Set

Answer 6

a given list of unordered elements that can use set theory
operations such as intersection and union

Question 7

Explain why the properties have been set to PRIVATE

Answer 7

To ensure that attributes can only be accessed by the class’s own methods
To enforce encapsulation// ensure theyre hidden

Question 8

Compare sequential and serial methods of file organisation

Answer 8

• In both serial and sequential files records are stored one after the other
• and need to be accessed one after the other
• Serial files are stored in chronological order
• Sequential files are stored with ordered records
• and stored in the order of the key field

Question 9

State the most suitable method of file access when a record is referenced by a unique address on a disk-type storage medium.

Answer 9

Direct (access)

Question 10

State the most suitable method of file access when a bank stores its data records in ascending order of account number.

Answer 10

Sequential (access)

Question 11

Describe how records are organised and accessed in a sequential file

Answer 11

records are stored in a particular order
MP2 the order is determined based on the value in a key field
MP3 records are accessed one after the other
MP4 records can be found by searching from the beginning of the file, record by record,
MP5 … until the required record is found or key field value is exceeded.

Question 12

Serial file organisation

Answer 12

a method of file organisation in which records of data are physically stored in a file, one after another, in the order they were added to the file

Question 13

Sequential file organisation

Answer 13

a method of file organisation in which records of data are physically stored in a file, one after another, in a given order

Question 14

Random file organisation

Answer 14

a method of file organisation in which records of data are physically stored in a file in any available position; the location
of any record in the file is found by using a hashing algorithm on the key field of a record.

Question 15

Hashing algorithm (file access)

Answer 15

a mathematical formula used to perform a calculation on the key field of the record; the result of the calculation gives the address where the record should be found.

Question 16

Sequential access

Answer 16

a method of file access in which records are searched one after another from the physical start of the file until the required record is found.

Question 17

Direct access

Answer 17

a method of file access in which
a record can be physically found in a file without physically reading other records

Question 18

how to deal with with key fields that have the same address

Answer 18

• An open hash where the record is stored in the next free space.
• A closed hash where an overflow area is set up and the record is stored in the next free space in the overflow area.

Question 19

Describe what happens, in relation to the storage or retrieval of a record in the file, when the calculated hash value is a duplicate of a previously calculated hash value for a different record key.

Answer 19

A collision occurs when the record key doesn’t match the stored record key
MP2 … this means the determined storage location has already been used
for another record.
If the record is to be stored
MP3 Search the file linearly
MP4 … to find the next available storage space (open hash)
MP5 Search the overflow area linearly
MP6 … to find next available storage space (closed hash)

Question 20

Explain what is meant by a user-defined composite data type. Include an example of another user-defined composite data type in your answer

Answer 20

A data type constructed by a programmer // not a primitive data type
 A data type that references at least one other data type…
the data types can be primitive, or user defined
Class / object / set