Basic concepts of Database Systems

1: the development stage of data management technology;

1.1: manual management stage;

Features: 1.1.1: data is not stored in the computer;

1.1.2: no special software is available to manage data;

1.1.3: only the concept of program, no file concept;

1.1.4: Data object-oriented;

 

1.2: File System stage;

Features: 1.2.1: data can be stored on an external storage disk in the form of files for a long time;

1.2.2: the logical and physical structures of data are different;

1.2.3: The file organizations have been diversified;

1.2.4: data no longer belongs to a specific program; it can be applied repeatedly, that is, data is oriented to applications;

1.2.5: operations on data are recorded in units;

1.3: Database stage;

1.3.1: Use a data model to represent a complex data structure;

1.3.2: high data independence;

1.3.3: the database system provides convenient user interfaces;

1.3.4: databases provide: database recovery, database concurrency control, data integrity, and data security

1.3.5: Increased system flexibility;

Database ):

DB is a collection of data that has been stored in a computer for a long time and is organized and managed in a unified manner.

Database Management System ):

DBMS is a layer of data management software between users and operating systems. It provides users or applications with methods to access the database, including database creation, query, update, and various data control;

DBMS: hierarchical, mesh, relational, and object-oriented;

Database System)

DBS is a system that stores a large amount of associated data in an organized and dynamic manner and allows multiple users to access computer hardware, software, and data resources;

Database Technology:

Database technology is a software science that studies the structure, storage, design, management, and use of databases;

 

2: Data Description terms;

2.1: Data Description in conceptual design;

2.1.1: Term: entity, entity set, attribute, entity identifier;

2.2: Data Description in physical design;

2.2.1: Term: field, record, file, key code

2.2.2: The storage media of computer systems can be divided into the following types:

High-speed buffer storage, primary storage, fast erase storage, disk storage, optical storage, disk

2.3: Data Description in logical design;

 

 

 

 

2.4: Data contact description;

A link is the mutual relationship between entities. The number of entity sets related to a link is called the original number of links;

There are one-to-one contacts, one-to-multiple contacts, and multiple-to-multiple contacts;

3: data abstraction level;

3.1: data abstraction process;

3.1.1: A Model of the Global Logical Structure of data that expresses user needs and views. It is called a conceptual model;

3.1.2: a model that expresses the global logical structure of the database for computer implementation. It is called a logical model;

3.1.3: An External Model is the model of the local logical structure of the database that expresses the user's opinion;

3.1.4: a model that expresses the physical structure of a database, called an "Internal Model";

3.2: Conceptual Model;

3.2.1: the conceptual model expresses the overall logical structure of the data. It is a comprehensive description of the data involved in the entire application project by the System user;

3.2.2: the conceptual model is used to model data from the perspective of user requirements;

3.2.3: the conceptual model is independent of hardware and software;

3.2.4: Conceptual Model is a tool for communication between database designers and users;

 

3.3: Logical Model;

3.3.1: the logical model expresses the overall logical structure of the database, but it is the full description of the Database of the entire application project by the designer;

3.3.2: the logical model is used to model data from the perspective of database implementation;

3.3.3: the logical model is independent of hardware but dependent on software;

3.3.4: logical model is a tool for communication between database designers and application programmers;

Logical models are mainly divided:

Hierarchical Model: a data model that uses a tree structure to represent object types and relationships between objects is called a hierarchical model;

Mesh model: a data model that uses a directed graph structure to represent the relationship between entities and entities is called a mesh model;

Relational Model: uses a two-dimensional table to express an object set;

External Model: In application systems, a number of business units are often divided based on the characteristics of the business. each business unit has specific constraints and requirements.

1) The external model is a logical subset of the logical model;

2) external models are independent of hardware and dependent on software;

3) The external model reflects the user's views on using the database;

 

3.4: Internal Model;

The internal model, also known as the physical model, is the abstraction of the lowest layer of the database. It describes the storage methods, access devices, and access methods of data on disk tapes;

3.5: External Model;

3.6: layer-3 mode and two-level image;

From the user to the database, there are three levels of DB Data Structure Description:

1) The external mode is the interface between the user and the database system. It is the description of the data used by the user. The external mode consists of multiple external record types;

2) the logical mode is the description of the overall logical structure of all data in the database. It consists of several logical record types and also includes the requirements for inter-record Association and data integrity and security;

3) The internal mode is the description of the Database in terms of physical storage. It defines the organization of all internal record types, indexes and files, as well as data control details;

 

There are two levels of images between the three layers:

1) The external mode/logical mode image exists between the external mode and the logical mode, and is used to define the correspondence between the external mode and the logical mode. This image is generally described in external mode;

2) logical mode/internal mode images exist between the logical mode and internal mode, and are used to define the correspondence between the logical mode and the internal mode. This image is generally described in the internal mode;

3.7: high data independence;

It means that the data structures of applications and databases are independent from each other. If you do not want to modify the data structure, try not to modify the application. In this case, the system achieves the Data independence goal;

 

4: Database Management System

4.1: working mode of DBMS;

1) accept application data requests and process requests;

2) convert users' data requests into complex machine code;

3) perform database operations;

4) accept query results from database operations;

5) process the query results;

6) return the processing result to the user;

 

4.2: main functions of DBMS;

1) database definition functions;

2) database operation functions;

3) database protection functions;

3.1: database recovery;

3.2: Database Concurrency Control;

3.3: Data Integrity Control;

3.4: Data Security Control;

4) data dictionary;

 

5: database system;

5.1: Composition of DBS;

1) database;

2) hardware;

3) software;

Database Administrator (DBA): A group of personnel who control the overall structure of data. They are responsible for normal operation of DBS and creation, monitoring, and maintenance of database structures;

Responsibilities:

1) define the mode;

2) define the internal mode;

3) Contact with the user;

4) define security rules and authorize users to access the database;

5) define integrity rules and monitor database operations;

6) database dumping and recovery;

5.2: global structure of dbs;

1) database users;

DBA, professional users, application programmers, and end users

2) DBMS query processor;

DDL interpreter, DML compiler, embedded DML pre-compiler, query evaluation value and;

3) DBMS Storage Manager

Permission and integrity manager, Transaction Manager, File Manager, buffer manager

4) Data Structure in disk storage;

Data files, data dictionaries, indexes, statistics, and logs

5.3: DBS benefits;