Giáo trình tổng hợp các cách sử dụng máy in laser một cách hiệu quả và tiết kiệm phần 5 ppsx

a. The records in logical file are brought into some sequence as determined

by key in the records.

b. A computer is capable of sorting record into a “nested” sequence.

c. Sorting is done by a “sorting generator”. This is part of the computer’s

software and comprises several sophisticated sorting techniques that are

called into use according to the file and the sort requirements.

d. The need of sorting has dimished in line with the demise of magnetic tape

as backing storage.

2. Merging

- Merging implies that two or more files in the same sequence are combined

into one file.

a. File merging

 Two or more separate files of similar seconds and in

the same sequence are marged together so as to

form one file.

b. Record merging

 The records from two or more “input” files, usually

in the same sequence, are combined one record in

the output file.

3. Matching

a. Two or more input files (generally in the same sequence) are compared

records against record in order to ensure that there is a complete set of

records for each key.

b. Masmatched records are highlighted for subsequent action

4. Summanizing

a. Records with the same key in one file are accumulated together to form

one record in the output file.

b. Summanizing usually applies to a file presorted into a certain sequence and

the resultant file is in the same sequence.

c. Records to be summarized are generally of a similar type.

5. Searching

a. Searching is looking for records with certain keys or holding certain data

and in some way making a note of these.

b. An instance is a search for and count of all records with a debt balance of

above a certain amount.

6. Information retrieval

a. Information retrieval is the process that involves the bringing together of

data from several files.

b. Data may also be extracted from several files and combined before being

presented as information.

Chapter 8: DIRECT ACCESS FILE ORGANIZATION AND STRUCTURES.

Question 1. Storage and Access Modes?

There are 3 principal modes for storing and accessing accords on a disk or drum:

1. Serial mode:

- The record are stored contigously regardless of their keys

- The sole way of accessing serial seconds is to search through the complete

file starting with the first record.

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