File Organization Notes
FILE DESIGN- The study of file structures involves the investigation of the data structures used to organize a large collection of data into one or more external files that are stored on secondary storage devices.
FILE - is a collection of related data. Example: payroll file
FILE ORGANIZATION -refers to the way in which records are stored in an external file - refers to the data structures used for organizing the data. FOUR COMMON FILE ORGANIZATIONS 1. SEQUENTIAL FILE ORGANIZATION - records are written consecutively - files are stored in ascending or descending order according to a key field. ADVANTAGE: - easier to maintain than other organizations – especially in terms of adding and deleting records
2. RANDOM FILE ORGANIZATION - implies a predictable relationship between the key used to identify an individual record and that record's location in an external file.
3. INDEXED SEQUENTIAL FILE ORGANIZATION- combines sequential access and ordering with the capabilities of random access.
Example: a simple linear search on a 1,000 record sequentially organized file. An average of 500 key comparisons is needed (and this assumes the search keys are uniformly distributed among the data keys). However, using an index evenly spaced with 100 entries, the total number of comparisons is reduced to 50 in the index file plus 50 in the data file: a five to one reduction in the operations count!
TWO PARTS OF INDEXED SEQUENTIAL FILE:
a. A collection of records stored in contiguous locations within blocks in a relative file and ordered by a key field.
b. An index (a hierarchical structure of record keys and relative block numbers) to the file of ordered records.
4. MULTIKEY FILE ORGANIZATION - allows access to a data file by several different key fields. Example: Library file that requires access by author and by subject matter and title.
DATA FILE TYPES
1. MASTER FILE - contains records of permanent data that are updated by
FILE - is a collection of related data. Example: payroll file
FILE ORGANIZATION -refers to the way in which records are stored in an external file - refers to the data structures used for organizing the data. FOUR COMMON FILE ORGANIZATIONS 1. SEQUENTIAL FILE ORGANIZATION - records are written consecutively - files are stored in ascending or descending order according to a key field. ADVANTAGE: - easier to maintain than other organizations – especially in terms of adding and deleting records
2. RANDOM FILE ORGANIZATION - implies a predictable relationship between the key used to identify an individual record and that record's location in an external file.
3. INDEXED SEQUENTIAL FILE ORGANIZATION- combines sequential access and ordering with the capabilities of random access.
Example: a simple linear search on a 1,000 record sequentially organized file. An average of 500 key comparisons is needed (and this assumes the search keys are uniformly distributed among the data keys). However, using an index evenly spaced with 100 entries, the total number of comparisons is reduced to 50 in the index file plus 50 in the data file: a five to one reduction in the operations count!
TWO PARTS OF INDEXED SEQUENTIAL FILE:
a. A collection of records stored in contiguous locations within blocks in a relative file and ordered by a key field.
b. An index (a hierarchical structure of record keys and relative block numbers) to the file of ordered records.
4. MULTIKEY FILE ORGANIZATION - allows access to a data file by several different key fields. Example: Library file that requires access by author and by subject matter and title.
DATA FILE TYPES
1. MASTER FILE - contains records of permanent data that are updated by