RDBMS in DB2 - IBM Mainframe

DB2 is an abbreviation for 'IBM DATABASE 2'. It is a Relational Database Management System for the MVS operating system. It is a system that allows the MVS users to build, access and maintain relational databases, using the well-known relational language SQL or Structured Query Language. DB2 databases are relational. A relational database is a database that is perceived by its users as a collection of tables and nothing but tables. Relational systems are based on what is called the relational model of data, which was described in many details in the previous chapters.

DB2, like any other relational database management systems, supports SQL. This language, which is used to formulate relational operations, i.e., operations that define and manipulate data in relational form is discussed in great detail in the next few chapters. Another significant feature of most relational systems, including DB2, is that the same relational language (like SQL) is available in two forms. These two interfaces are interactive interface and application programming interface.

Today, DB2 represents a portfolio of information management products, with far-reaching and worldwide application. DB2 is optimized for the rapidly growing clustered server market that focuses on high availability and disaster recovery. Today, more than 60 million DB2 users from 425,000 companies worldwide rely on IBM DB2 Information Management Solutions.

The interactive interface of DB2 is called 'DB2I' or 'DB2 Interactive'. Thus SQL is both an interactive query language and a database programming language. This applies to any SQL statement, which means that, any SQL statement that can be entered at the terminal in the interactive mode can be embedded in the program also. In DB2, the SQL statements can be used all of the following host languages—C, COBOL, FORTRAN. PL/I and System /370 Assembler language.

More than one user can use the DB2 systeniHat1^ time. Usually there will be many users, all operating in the same data at the same time. DB2 will automatically apply the necessary controls to ensure the interests of the users and the system are safeguarded.

For instance, DB2 will guarantee that one user's updates cannot cause another user's operations to produce an incorrect result. The users can be application programs, which use embedded SQLs or interactive DB2 users.

Like there are two kinds of users, there are two kinds of DB2 tables, base-tables and views. A base-table (described in detail in the next chapter) is real table that physically exists, i.e., there are physically stored records and physical indexes in one ore MVS files (VSAM detests).

A view on the other hand is a virtual table, a table that does not physically exist, but looks to the user as if it did. A view can be thought of as different ways of looking at the base tables. The DB2 from a user's point of view is represented in the following figure.

DB2 as Seen by an Individual

DB2 as Seen by an Individual

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