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INTRODUCTION TO DATABASE SYSTEM TOPICS TO BE DISCUSSED…………… Meaning of Database Characteristics of Database Database System Advantages of Database System Disadvantages of Database System DATABASE Database is a collection of related information stored so that it available to many users for different purposes. The content of database is obtained by combining data from all the different sources in an organization. So that data are available to all users and redundant data can be eliminated A database is well organized collection of data that are related in a meaningful way which can be accessed in different logical orders but are stored only once. CHARACTERISTICS OF DATABASE Database represents some aspects of real world application. Any change in real world are reflected in database. A database is designed and built with data for specific purposes. It has intended group of users and applications in which these users rae interested. Operations like update, insert, retrieve etc. on the database can be carried out in simple and flexible way. A database provides logical relationship between its records and data. Thus various records can be accessed depending on some logical conditions by a single query from the database DATABASE SYSTEM A database system consist of a collection of interrelated data and a set of programs to access the data. Hence database system is the DBMS software together with the data itself. It is a software that assist in maintaining and utilizing a database. A Database Management System consist of : A collection of interrelated data. This part of DBMS is usually referred to as the database A set of application programs used to access, update manage that data. This portion forms Data Management System. The purpose or goal of database system is to provide an environment that is both convenient and efficient to use in : Retrieving information from database and Storing information into database In other words, a DBMS allows you to store, update and retrieve data hence making it easy to maintain and retrieve information from a database. The following figure shows simplified database system environment: USERS DATABASE SYSTEM DBMS Software Queries Software to process Queries Software to Access Stored Data Stored Database Definitions Stored Database The database system contains not only the database itself but also a complete definition or description of the database structure and constraints. This definition is stored in system catalog. The information stored in catalog is called d metadata i.e. data about data. An important property of database system is that the structure of data files is stored in the DBMS catalog separately from the access programs. This is known as program-data independence. Due to this property, we can change the structure of data files in the catalog but no need to change the programs. ADVANTAGES OF DATABASE SYSTEM Database approach came into existence due to the bottlenecks of file processing system. In the database approach, the data is stored at a central location and is shared among multiple users. Thus, the main advantage of DBMS is centralized data management. The centralized nature of database system provides several advantages, which overcome the limitations of the conventional file processing system. These advantages are listed here. Controlled data redundancy: During database design, various files are integrated and each logical data item is stored at central location. This eliminates replicating the data item in different files, and ensures consistency and saves the storage space. Note that the redundancy in the database systems cannot be eliminated completely as there could be some performance and technical reasons for having some amount of redundancy. However, the DBMS should be capable of controlling this redundancy in order to avoid data inconsistencies. Enforcing data integrity: In database approach, enforcing data integrity is much easier. Various integrity constraints are identified by database designer during database design. Some of these data integrity constraints can be enforced automatically by the DBMS, and others may have to be checked by the application programs. Data sharing: The data stored in the database can be shared among multiple users or application programs. Moreover, new applications can be developed to use the same stored data. Due to shared data, it is possible to satisfy the data requirements of the new applications without having to create any additional data or with minimal modification. Ease of application development: The application programmer needs to develop the application programs according to the users’ needs. The other issues like concurrent access, security, data integrity, etc., are handled by the DBMS itself. This makes the application development an easier task. Data security: Since the data is stored centrally, enforcing security constraints is much easier. The DBMS ensures that the only means of access to the database is through an authorized channel. Hence, data security checks can be carried out whenever access is attempted to sensitive data. To ensure security, a DBMS provides security tools such as user codes and passwords. Different checks can be established for each type of access (addition, modification, deletion, etc.) to each piece of information in the database Multiple user interfaces: In order to meet the needs of various users having different technical knowledge, DBMS provides different types of interfaces such as query languages, application program interfaces, and graphical user interfaces (GUI) that include forms-style and menu-driven interfaces. A form-style interface displays a form to each user and user interacts using these forms. In menu-driven interface, the user interaction is through lists of options known as menus. Backup and recovery: The DBMS provides backup and recovery subsystem that is responsible for recovery from hardware and software failures. For example, if the failure occurs in between the transaction, the DBMS recovery subsystem either reverts back the database to the state which existed prior to the start of the transaction or resumes the transaction from the point it was interrupted so that its complete effect can be recorded in the database. Program-data independence: The independence between the programs and the data is known as program data independence or data independence It is an important characteristic of DBMS as it allows changing the structure of the database without making any changes in the application programs that are using the database. Data abstraction: The property of DBMS that allows program-data independence is known as data abstraction. Data abstraction allows the database system to provide an abstract view of the data to its users without giving the physical storage and implementation details. Supports multiple views of the data: A database can be accessed by many users and each of them may have a different perspective or view of the data. A database system provides a facility to define different views of the data for different users. A views a subset of the database that contains virtual data derived from the database files but it does not exist in physical form. That is, no physical file is created for storing the data values of the view; rather, only the definition of the view is stored. DISADVANTAGES OF DATABASE SYSTEM High Cost Because a complete DBMS is very large and sophisticated piece of software, it is expensive to purchase. High Hardware Cost Additional memory and processing power may be require to run the DBMS. This results need to upgrade the hardware. High Programming Cost Because a DBMS is a complex tool with many features, it requires experienced programmers which result in extra payment for their hire and expertise. Backup and Recovery are more Difficult This is because of increased complexity and because databases are often processed by several users concurrently. Determining the exact state of database at the time of failure may be a problem. Data Integrity Since a large number of users could be using a database concurrently technical safe guards are necessary to ensure that the data remain correct during operation. The main threat to data integrity comes from several different users attempting to update same data at the same time. THANKS