Cơ sở dữ liệu - Chapter 1: Overview of database management system

Chapter 1 Overview of Database Management System Objectives  Overview of DBMS  An Example  Characteristics of the Database  DBMS vs. File-based system  Advantages of using the DBMS approach Data and Information  Data: ◦ Raw facts that constitute building block of information. ◦ The heart of the DBMS.  All the data will not convey useful information.  Data Information processed Collection of information metadata Data Database  A database: ◦ A collection of data that are related in a meaningful way, which can be accessed in different logical orders.  The main features of the data in the database: ◦ Well organized (structured) ◦ Related ◦ Accessible in different orders Database example  Book airline ticket  Register a new course in university  Buy book in the bookstore  Library management  Database Simplified database view Database Management System  DBMS ◦ A general purpose software package designed to store and manage database.  DBMS is helpful in maintaining and utilizing a database. Database Management System Capabilities of database management system Data dictionary  Data dictionary or “system catalog” ◦ A centralized store of information about the database. ◦ Contain information about the tables, the fields the tables contain, data types, primary keys, indexes, the joins which have been established between those tables, referential integrity, cascades update, cascade delete, etc. Metadata  Metadata: ◦ the information (data) about the data in a database. ◦ Available for query and manipulation, just as other data in the database Database Models  A collection of tools for describing the database (include data, relationships, sematics, constraints) at a level of abstraction  Levels of abstraction: ◦ Conceptual Data Model:  a high level description useful for requirements understanding. ◦ Representational Data Model  describing the logical representation of data without giving details of physical representation. ◦ Physical Data Model  description giving details about record formats,file structures etc. Objectives  Overview of DBMS  An Example  Characteristics of the Database  DBMS vs. File-based system  Advantages of using the DBMS approach The University Database  The University Database Context: maintaining information concerning students, courses, and grades in a university environment.  STUDENT file stores data on each student  COURSE file stores data on each course  SECTION file stores data on each section of each course  GRADE_REPORT file stores the grades that students receive  PREREQUISITE file stores the prerequisites Objectives  Overview of DBMS  An Example  Characteristics of the Database  Advantages of using the DBMS approach Database Management System  Objectives of DBMS: ◦ Data availability: users can easily access the data. ◦ Data integrity: the data available in the database is a reliable data ◦ Data security: only authorized users can access the data. Data security can be enforced by passwords. ◦ Data Independence: DBMS allows the user to store, update, and retrieve data in an efficient manner. File-Based System vs. DBMS  Duplication of data: same data being stored more than once.  Data dependence: the application program depends on the data  Incompatible file formats: the structure of the file depends on the application programming language.  Separation, and isolation of data: must synchronize the processing of two files to ensure that the correct data are extracted. If data has to be retrieved from more than two files  difficult to access. The levels of data abstraction The levels of data abstraction  Physical level or internal level: ◦ the physical storage of the information ◦ complex low-level data structures in detail  Logical level or conceptual level: ◦ describes what data are stored in the database and what relationships exist among those data. ◦ the entire database in terms of a small number of simple structures.  View level or external level: ◦ the highest level of abstraction. It is the view that the individual user of the database has. ◦ There can be many view level abstractions of the same data. People Interacting with Database People interacting with database Database Administrator Database Designer Database User Application Programmer End-user Objectives  Overview of DBMS  An Example  Characteristics of the Database  Advantages of using the DBMS approach Advantages of DBMS  Centralized data management: ◦ Reducing redundancies ◦ Making data management more efficient ◦ Providing persistent storage of program objects and data structures ◦ Providing Backup and Recovery facilities  Data Independence: ◦ programs are isolated from changes in the way the data are structured and stored. ◦ DBMS provides the interface between the application programs and the data. Advantages of DBMS  Data consistency: ◦ Enforcing Integrity Constraints so as to maintain the consistency of database  Data Security ◦ Restricting unauthorized access  Providing multiple user interfaces Review  What is Database? Give an example.  Define – DBMS  What are the advantages of using DBMS? Summary  The main objective of database management system is to store and manipulate the data in an efficient manner.  A database is an organized collection of related data.  All the data will not give useful information. Only processed data gives useful information, which helps an organization to take important decisions.