RDBMS CONCEPTS

•         What are the different phases of transaction?

Different phases are

Ø  Analysis phase

Ø  Redo Phase

Ø  Undo phase

•           What do you mean by flat file database?

It is a database in which there are no programs or user access languages. It has no cross-file capabilities but is user-friendly and provides user-interface management.

•            What is "transparent DBMS"?

It is one, which keeps its Physical Structure hidden from user.

•             Brief theory of Network, Hierarchical schemas and their properties

Network schema uses a graph data structure to organize records example for such a database management system is CTCG while a hierarchical schema uses a tree data structure example for such a system is IMS.

•            What is a query?

            A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.

•             What do you mean by Correlated subquery?

            Subqueries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery.

A correlated subquery can be easily identified if it contains any references to the parent subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery.

 E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)

•           What are the primitive operations common to all record management systems?

Addition, deletion and modification.

•             Name the buffer in which all the commands that are typed in are stored

            ‘Edit’ Buffer

•          What are the unary operations in Relational Algebra?

            PROJECTION and SELECTION.

            Are the resulting relations of PRODUCT and JOIN operation the same?

            No.

            PRODUCT: Concatenation of every row in one relation with every row in another.

            JOIN: Concatenation of rows from one relation and related rows from another.

•         What is RDBMS KERNEL?

            Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database

            You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures

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•             Name the sub-systems of a RDBMS

            I/O, Security, Language Processing, Process Control, Storage Management, Logging and Recovery, Distribution Control, Transaction Control, Memory Management, Lock Management

•             Which part of the RDBMS takes care of the data dictionary? How

            Data dictionary is a set of tables and database objects that is stored in a special area of the database and maintained exclusively by the kernel.

•             What is the job of the information stored in data-dictionary?

            The information in the data dictionary validates the existence of the objects, provides access to them, and maps the actual physical storage location.

• Not only RDBMS takes care of locating data it also

            determines an optimal access path to store or retrieve the data

•       How do you communicate with an RDBMS?

            You communicate with an RDBMS using Structured Query Language (SQL)

•           Define SQL and state the differences between SQL and other conventional programming Languages

SQL is a nonprocedural language that is designed specifically for data access operations on normalized relational database structures. The primary difference between SQL and other conventional programming languages is that SQL statements specify what data operations should be performed rather than how to perform them.

•            Name the three major set of files on disk that compose a database in Oracle

There are three major sets of files on disk that compose a database. All the files are binary.  These are

Ø  Database files

Ø  Control files

Ø  Redo logs

The most important of these are the database files where the actual data resides. The control files and the redo logs support the functioning of the architecture itself.

All three sets of files must be present, open, and available to Oracle for any data on the database to be useable. Without these files, you cannot access the database, and the database administrator might have to recover some or all of the database using a backup, if there is one.

•          What is an Oracle Instance?

The Oracle system processes, also known as Oracle background processes, provide functions for the user processes—functions that would otherwise be done by the user processes themselves

Oracle database-wide system memory is known as the SGA, the system global area or shared global area. The data and control structures in the SGA are shareable, and all the Oracle background processes and user processes can use them.

The combination of the SGA and the Oracle background processes is known as an Oracle instance

          What are the four Oracle system processes that must always be up and running for the database to be useable

            The four Oracle system processes that must always be up and running for the database to be useable include DBWR (Database Writer), LGWR (Log Writer), SMON (System Monitor), and PMON (Process Monitor).