Unit-2

DBMS languages

Database languages are used to read, update and store data in a database. There are several such languages that can be used for this purpose; one of them is SQL (Structured Query Language).

·         DDL (Data Definition Language): used (by the DBA and/or database designers) to specify the conceptual schema.

·         SDL (Storage Definition Language): used for specifying the internal schema

·         VDL (View Definition Language): used for specifying the external schemas (i.e., user views)

·         DML (Data Manipulation Language): used for performing operations such as retrieval and update upon the populated database

The above description represents some kind of ideal. In real-life, at least so far, the standard DBMS language is SQL (Standard Query Language), which has constructs to support the functions needed by DDL, VDL, and DML languages.

Types of DBMS languages:

Data Definition Language (DDL)

DDL is used for specifying the database schema. It is used for creating tables, schema, indexes, constraints etc. in database. Lets see the operations that we can perform on database using DDL:

·         To create the database instance – CREATE

·         To alter the structure of database – ALTER

·         To drop database instances – DROP

·         To delete tables in a database instance – TRUNCATE

·         To rename database instances – RENAME

·         To drop objects from database such as tables – DROP

·         To Comment – Comment

All of these commands either defines or update the database schema that’s why they come under Data Definition language.

Data Manipulation Language (DML)

DML is used for accessing and manipulating data in a database. The following operations on database comes under DML:

·         To read records from table(s) – SELECT

·         To insert record(s) into the table(s) – INSERT

·         Update the data in table(s) – UPDATE

·         Delete all the records from the table – DELETE

Data Control language (DCL)

DCL is used for granting and revoking user access on a database –

·         To grant access to user – GRANT

·         To revoke access from user – REVOKE                                             (officially cancel)

In practical data definition language, data manipulation language and data control languages are not separate language, rather they are the parts of a single database language such as SQL.

Transaction Control Language(TCL)

The changes in the database that we made using DML commands are either performed or rollbacked using TCL.

·         To persist the changes made by DML commands in database – COMMIT

·         To rollback the changes made to the database – ROLLBACK

  

2.4       Database Users

Reference: https://www.tutorialcup.com/dbms/database-users-administrators.htm

Database users are the one who really use and take the benefits of database. There will be different types of users depending on their need and way of accessing the database.

Application Programmers - They are the developers who interact with the database by means of DML queries. These DML queries are written in the application programs like C, C++, JAVA etc. These queries are converted into object code to communicate with the database. For example, writing a C program to generate the report of employees who are working in particular department will involve a query to fetch the data from database. It will include a embedded SQL query in the C Program.

Sophisticated Users - They are database developers, who write SQL queries to select/insert/delete/update data. They do not use any application or programs to request the database. They directly interact with the database by means of query language like SQL. These users will be scientists, engineers, analysts who thoroughly study SQL and DBMS to apply the concepts in their requirement. In short, we can say this category includes designers and developers of DBMS and SQL.

Specialized Users - These are also sophisticated users, but they write special database application programs. They are the developers who develop the complex programs to the requirement.

Stand-alone Users - These users will have stand –alone database for their personal use. These kinds of database will have readymade database packages which will have menus and graphical interfaces.

Native Users - these are the users who use the existing application to interact with the database. For example, online library system, ticket booking systems, ATMs etc which has existing application and users use them to interact with the database to fulfill their requests.

Database Administrators

The life cycle of database starts from designing, implementing to administration of it. A database for any kind of requirement needs to be designed perfectly so that it should work without any issues. Once all the design is complete, it needs to be installed. Once this step is complete, users start using the database. The database grows as the data grows in the database. When the database becomes huge, its performance comes down. Also accessing the data from the database becomes challenge. There will be unused memory in database, making the memory inevitably(as is certain to happen) huge. These administration and maintenance of database is taken care by database Administrator – DBA.

A DBA has many responsibilities. A good performing database is in the hands of DBA.

· Installing and upgrading the DBMS Servers: - DBA is responsible for installing a new DBMS server for the new projects. He is also responsible for upgrading these servers as there are new versions comes in the market or requirement. If there is any failure in up-gradation of the existing servers, he should be able revert the new changes back to the older version, thus maintaining the DBMS working. He is also responsible for updating the service packs/ hot fixes/ patches to the DBMS servers.

· Design and implementation: - Designing the database and implementing is also DBA’s responsibility. He should be able to decide proper memory management, file organizations, error handling, log maintenance etc for the database.

· Performance tuning: - Since database is huge and it will have lots of tables, data, constraints and indices, there will be variations in the performance from time to time. Also, because of some designing issues or data growth, the database will not work as expected. It is responsibility of the DBA to tune the database performance. He is responsible to make sure all the queries and programs works in fraction of seconds.

· Migrate database servers: - Sometimes, users using oracle would like to shift to SQL server or Netezza. It is the responsibility of DBA to make sure that migration happens without any failure, and there is no data loss.

· Backup and Recovery: - Proper backup and recovery programs needs to be developed by DBA and has to be maintained him. This is one of the main responsibilities of DBA. Data/objects should be backed up regularly so that if there is any crash, it should be recovered without much effort and data loss.

· Security: - DBA is responsible for creating various database users and roles, and giving them different levels of access rights.

· Documentation: - DBA should be properly documenting all his activities so that if he quits or any new DBA comes in, he should be able to understand the database without any effort. He should basically maintain all his installation, backup, recovery, security methods. He should keep various reports about database performance.

In order to perform his entire task, he should have very good command over DBMS.