The logical structure of the database file is a record file. The logical structure of files can be divided into two categories: 1. Unstructured streaming files, which refer to files that no longer divide the information into units. They are files composed of a sequence of character streams; 2. Structured record files , the user divides the information in the file into information units according to logically independent meanings, and each unit is called a logical record. The files studied by the database are a set of records with a structure. Each record can be composed of several data items. Therefore, the logical structure of the database file is a structured record file.
The operating environment of this tutorial: Windows 7 system, Dell G3 computer.
The logical structure of the file is the user-visible structure.
Logical files are structurally divided into two forms:
One is an unstructured streaming file, which means that the information in the file is no longer divided. Unit, which is a file composed of a sequence of character streams.
One type is a structured record file. The user divides the information in the file into logically independent units. Each unit is called a logical record (referred to as a record). ).
All records usually describe an entity set, with the same or different numbers of data items. The length of the records can be divided into fixed-length and variable-length records.
The logical structure of the database file is a structured record file.
Structured record files
When the operating system or database is running, the computer will record some information in files. These files This can be called a log file. The record is the basic unit of access in the file.
A file (File) is a collection of records with the same nature. The data volume of the file is usually large and is placed on external storage. They are divided into two categories according to their record types: operating system files and database files.
One type of file studied by the operating system is an unstructured streaming file, which means that the information in the file is no longer divided into units. It is a file composed of a string of character streams.
The file studied by the database is a set of records with a structure, and each record can be composed of several data items.The files can also be divided into fixed-length record files and variable-length record files according to the length characteristics of the records. Each record in the file contains the same length of information, which is called a fixed-length record file. Otherwise, it is called an indefinite-length record file.
Record:
Record is a group A collection of related data items used to describe an object's properties in some aspect. Which data items a record should contain depends on which aspect of the object needs to be described. An object can be regarded as different objects due to the different environments in which it is located. For example, when a student is regarded as a student in the class, his description should use his student number, name, age and department class, and may also include the name of the courses he has studied, grades and other data. item. However, if a student is regarded as a medical object, the data items describing him should use items such as medical record number, name, gender, date of birth, height, weight, blood pressure, and medical history.
In order to uniquely identify a record among many records, one or several data items must be identified among each data item of a record, and their set is called a key. In other words, a keyword is the only data item that can identify a record. Typically, only one data item is used as a key. For example, the preceding medical record number or student number can be used to identify a unique record among many records. However, sometimes such data items cannot be found, and several data items have to be defined as keywords that can uniquely identify a certain record among many records.
Logical structure and physical structure of records
The logical structure of records refers to the way it is presented in front of users or applications, and is the user’s representation and access of data. Way.
The physical structure of a record is the way data is stored on physical memory and is the physical representation and organization of the data.
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