database management system (DBMS) - IBM Mainframe

Before we attempt to define what a database, management system (DBMS) is, we must have a clear understanding of what the DBMS is managing—the database. A database consists of four elements as shown in the following figure:

  • Data
  • Relationships
  • Constraints
  • Schema

Data are binary computer representations of stored logical entities. They are distinct pieces of information, usually formatted in a special way. Software is divided into two general categories—data and programs. A program is a collection of instructions for manipulating data. Data can exist in a variety of forms—as numbers or text on pieces of paper, as bjts and bytes stored in electronic memory, or as facts stored in a person's mind.

Strictly speaking, data is the plural of datum—a single piece of information. In practice, however, people use data as both the singular and plural form of the word. The term data is often used to distinguish binary (machine-readable) information from textual (human-readable) information. For example, some applications make a distinction between data files (files that contain binary data) and text files (files that contain ASCII data).

In database management systems, data files are the files that store the database information, whereas other files, such as index files and data dictionaries, store administrative information known as metadata. Relationships represent a correspondence between the various data elements. Constraints are predicates that define correct database states. Schema describes the organization of data and relationships within the database.

Components of a Database

Components of a Database

Organization of a Database

Organization of a Database

The schema defines various views of the database for the use of the various system components of the database management system and for the applications' security. A schema separates the physical aspects of data storage from the logical aspects of data representation.

The internal schema defines how and where data are organized in physical data storage. The conceptual schema defines the stored data structures in terms of the database model used. The external schema defines a view or views of the database for particular users. A database management system provides services for accessing the database while maintaining the required correctness and consistency of the stored data.

A collection of data designed to be used by different people is called a database. It is a collection of interrelated data stored together with controlled redundancy to serve one or more applications in an optimal fashion. The data are stored in such a fashion that they are independent of the programs of people using the data. A common and controlled approach is used in adding new data and modifying and retrieving existing data within the database.

A database is organized in such a way that a computer program can quickly select desired pieces of data. You can think of a database as an electronic filing system. Traditional databases are organized by fields, records, and files. A field is a single piece of information; a record is one complete set of fields; and a file is a collection of records. For example, a telephone book is analogous to a file. It contains a list of records, each of which consists of three fields: name, address, and telephone number. To access information from a database, you need a database management system (DBMS).

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