structure of DBMS

7/28/2019 structure of DBMS

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Components of DBMS

Module - 1


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Major components of a DBMS

1. Transaction management:2. Concurrency Control:

3. Recovery Management:

4. Security Management:

5. Language Interface:

6. Storage Management:


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Transaction management

A transaction is a sequence of database operations that

represents a logical unit of work and that accesses adatabase and transforms it from one state to another.

For e.g. consider a database that holds information aboutairline reservations

Several travel agents look up information about available seats onvarious flights and make new seat reservation

When several users access a database concurrently, DBMS must ordertheir requests carefully to avoid conflicts.

DBMS must protect users from the effects of system failures byensuring that all data is restored to a consistent state


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Concurrency Control

This is the database management activity of coordinating the

actions of database manipulation processes that operateconcurrently that access shared data and potentially interfere

with one another

To schedule concurrent accesses to data so that each usercan safely ignore the fact that others are accessing the dataconcurrently

DBMS allows users to think of their programs as if they were executingin isolation

Locking protocol a set of rules to be followed by each transaction

Lock mechanism used to control access to database objects

Shared LOCK - Data item can only be read

Exclusive LOCK - Data item can be both read as well as written.


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Recovery Management

This in a database ensures the aborted or failedtransactions (system crash) create no adverseeffects on the database or the other transactions

DBMS must ensure that the changes made by such incomplete

transactions are removed from the databaseDBMS maintains a log of all writes to the database. Each write action must

be recorded in the log before the corresponding change is reflected inthe database itself. Property is called Write-Ahead Log or WAL

Security Management:Refers to the protection ofdata against un-authorized access


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Language Interface:The DBMS provides supportlanguages for definition and manipulation of data in thedatabase.

Storage Management:The DBMS provides amechanism for management of permanent storage of thedata.


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Structure of a DBMS


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Nave Users Application Sophisticated Database(tellers, agents etc.) programmers users Administrator

Applicationinterfaces

ApplicationPrograms Query

Databasescheme

Application programsobject code

DML compiler DDLinterpreter

Query Evaluation engine

Transaction manager Buffer manager

File manager

Embedded DMLpre compiler

indices Statistical data

Data filesData dictionary

users

Disk storage

Query

processor

Storagemanager

Authorization & Integrity manager


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Overall system structure

DBMS is divided into modules that deals with each of theresponsibilities of the overall system.

Functional components of a DBMS are

Query processor componentsStorage manager components


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Query Processor

components

DML compiler

Embedded DML precompiler

DDL interpreter

Query evaluation engine

Storage manager

components

Authorization and integritymanager

Transaction manager

File manager

Buffer manager


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DDL interpreter

Interprets DDL statements andrecords them in a set of tables

containing metadata

Query evaluation engine

Executes low-level instructionsgenerated by the DML compiler


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Authorization & integrity manager

Tests for the satisfaction of integrityconstraints and checks the

authority of users to access data.

Transaction manager

Ensures that the database remainsin a consistent state despite systemfailures.


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File manager

Manages the allocation of space ondisk storage and the data

structures used to representinformation stored on disks.

Buffer manager

Responsible for fetching data fromdisk storage into main memory anddeciding what data to cache in

memory.


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Several data structures required forphysical system implementation

Data files- which store the database itself

Data dictionary- stores metadata about the structure

of the database

Indices- provides fast access to data items that hold

particular values.

Statistical data- stores statistical information about

the data in the database.


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Database languages

DDL (Data definition language)

DML (Data manipulation language)

SDL (Storage Definition Language)VDL (View Definition Language)


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Data definition language

Database schema is specified by a set of definitionswhich are expressed by a special language calledDDL.

Result of compilation of DDL statements is a set oftables which are stored in a special file called datadictionary.


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create table branch

(branch-name char(15) not null,branch-citychar(30),assets integer)

DROPTABLE employees;

ALTERTABLE sink ADD bubbles INTEGER;

ALTERTABLE sink DROPCOLUMN bubbles;


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Data Dictionary

It is a file that contains metadata.

i.e. data about data

includes the names and descriptions of various tables and fields in eachdatabase, plus additional details, like the type and length of each data

element


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Data manipulation language

DML is a language that enable users to access or manipulate data indatabase.

selectA1,A2, ...,An

fromr1, r2, ..., rmwhere P

Insert into table tablename values (d1,d2..);

Delete from table tablename where condition ;

Update command


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Data manipulation means

Retrieval of information stored in the database.

Insertion of information into the database

Deletion of information from the database

Modification of information in database.


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Two types of DML

Procedural DML

require a user to specify what data are needed and how to get those data.

Non Procedural DML

require a user to specify what data are needed without specifying how to

get those data.


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SDL (Storage Definition Language): is used to specify theinternal schema.

VDL (View Definition Language): is used to specify userviews and their mappings to the conceptual schema.

Most DBMSs use DDL to specify both conceptual andexternal schema


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Query: A statement requesting the retrieval ofinformation

Query languageThe portion of a DML that involves informationretrieval

Data sublanguage: DML & DDL when embeddedwithin a host language (e.g C or COBOL)


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Database Users & Administrators

People who work with a database can becategorized as database users and databaseadministrators


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Types of database users

Nave users

unsophisticated users interacting with system byinvoking one of the application programs that ve

been written previously.e.g bank teller transfers $50 from account A to B byinvoking a program called transfer


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Application programmers

computer professionals who write application

programs like transfer.

Sophisticated users

interact without writing programs. They form theirrequests in query language.

Specialized users

sophisticated users who write specializeddatabase applications.

E.g CAD systems and Expert systems


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Database Administrator

A person who has a central control over the systemis called a DBA


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Functions of DBA

Schema Definition

DBA creates the original database schema by executing datadefinition statements in DDL


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Schema and physical organization modification

DBA makes changes to the schema and physicalorganization to reflect the changing needs of the organization

To ensure adequate performance as requirements change

Also known as database tuning


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Granting of authorization for data access

DBA is responsible for ensuring that unauthorized dataaccess is not permitted

DBA grants different types of authorization by which DBAregulates which parts of the database various users canaccess.


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Routine maintenance

Periodically backing up the database

Maintains logs of system activity

To facilitate recovery from a crash

Ensuring that enough free disk space is available for normaloperations

Monitoring jobs running on the database and ensuring itsperformance


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END

structure of DBMS

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