ch13 Flashcards
User-defined data type
a data type based on an existing data type or other data types that have been defined by a programmer
Describe the purpose of a user-defined data type
To create a new data type (from existing data types). and to allow data types not available in a programming language to be
constructed
Non-composite data type
a data type that does not reference any other data types.
Enumerated data type
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
Pointer data type
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
Set
a given list of unordered elements that can use set theory
operations such as intersection and union
Explain why the properties have been set to PRIVATE
To ensure that attributes can only be accessed by the class’s own methods
To enforce encapsulation// ensure theyre hidden
Compare sequential and serial methods of file organisation
- 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
State the most suitable method of file access when a record is referenced by a unique address on a disk-type storage medium.
Direct (access)
State the most suitable method of file access when a bank stores its data records in ascending order of account number.
Sequential (access)
Describe how records are organised and accessed in a sequential file
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.
Serial file organisation
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
Sequential file organisation
a method of file organisation in which records of data are physically stored in a file, one after another, in a given order
Random file organisation
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.
Hashing algorithm (file access)
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.
Sequential access
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.
Direct access
a method of file access in which
a record can be physically found in a file without physically reading other records
how to deal with with key fields that have the same address
- 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.
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.
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)
Explain what is meant by a user-defined composite data type. Include an example of another user-defined composite data type in your answer
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
