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Data Base Management System A database is an organized collection of data. The data is typically organized to model relevant aspects of reality (for example, the availability of rooms in hotels), in a way that supports processes requiring this information (for example, finding a hotel with vacancies). A DBMS makes it possible for end users to create, read, update and delete data in a database. The DBMS essentially serves as an interface between the database and end users or application programs, ensuring that data is consistently organized and remains easily accessible. The DBMS manages three important things: the data, the database engine that allows data to be accessed, locked and modified -- and the database schema, which defines the database’s logical structure. These three foundational elements help provide concurrency, security, data integrity and uniform administration procedures. Typical database administration tasks supported by the DBMS include change management, performance monitoring/tuning and backup and recovery. Many database management systems are also responsible for automated rollbacks, restarts and recovery as well as the logging and auditing of activity. The DBMS is perhaps most useful for providing a centralized view of data that can be accessed by multiple users, from multiple locations, in a controlled manner. A DBMS can limit what data the end user sees, as well as how that end user can view the data, providing many views of a single database schema. End users and software programs are free from having to understand where the data is physically located or on what type of storage media it resides because the DBMS handles all requests. The DBMS can offer both logical and physical data independence. That means it can protect users and applications from needing to know where data is stored or having to be concerned about changes to the physical structure of data (storage and hardware). As long as programs use the application programming interface (API) for the database that is provided by the DBMS, developers won't have to modify programs just because changes have been made to the database. The DBMS serves as the intermediary between the user and the database. The database structure itself is stored as a collection of files, and the only way to access the data in those files is through the DBMS. The DBMS presents the end user (or application program) with a single, integrated view of the data in the database. The DBMS receives all application requests and translates them into the complex operations required to fulfill those requests. The DBMS hides much of the database’s internal complexity from the application programs and users. The application program might be written by a programmer using a programming language such as C#, Java, or Visual Basic.NET, or it might be created through a DBMS utility program. Having a DBMS between the end user’s applications and the database offers some important advantages. Mainly the DBMS enables the data in the database to be shared among multiple applications or users. Also, the DBMS integrates the many different users’ views of the data into a single all-encompassing data repository. A DBMS provides advantages such as: • Improved data security. The more users access the data, the greater the risks of data security breaches. Corporations invest considerable amounts of time, effort, and money to ensure that corporate data are used properly. A DBMS provides a framework for better enforcement of data privacy and security policies. • Better data integration. Wider access to well-managed data promotes an integrated view of the organization’s operations and a clearer view of the database. It becomes much easier to see how actions in one part of the company affect other parts. • Better data access. The DBMS makes it possible to produce quick answers to ad hoc queries. From a database perspective, a query is a specific request issued to the DBMS for data manipulation—for example, to read or update the data. Simply put, a query is a question, and an ad hoc query is a spur-of-the-moment question. The DBMS sends back an answer (called the query result set) to the application. For example, when dealing with large amounts of sales data, end users might want quick answers to questions (ad hoc queries). • Improved data sharing. The DBMS helps create an environment in which end users have better access to more and better-managed data. Such access makes it possible for end users to respond quickly to changes in their environment. • Minimized data inconsistency. Data inconsistency exists when different versions of the same data appear in different places. For example, data inconsistency exists when a company’s sales department stores a sales representative’s name as James and the company’s personnel department stores that same person’s name as Ronny, or when the company’s regional sales office shows the price of a product as $85.06 and its national sales office shows the same product’s price as $90.50. The probability of data inconsistency is greatly reduced in a properly designed database. The Database System Environment The term database system refers to an organization of components that define and regulate the collection, management, storage, and use of data within a database environment. From a general management point of view, the database system is composed of the five major parts : hardware, software, procedures, people, and data. • Hardware refers to all of the system’s physical devices, including computers (PCs, workstations, servers, and supercomputers), storage devices, printers, network devices (hubs, switches, routers, fiber optics), and other devices (automated teller machines, ID readers, and so on). • Software: Although the most readily identified software is the DBMS itself, three types of software are needed to make the database system function fully: DBMS software, operating system software, and application programs and utilities.