DBMS architecture &; system structure

1. DBMS Architecture &
System structure of DBMS
• Asst.Prof. Rupali Lohar
• Dept. of Computer Science & Engineering
• B. R. Harne College Of Engineering & Technology, Karav, Post Vangani (W Tal Ambernath, Mumbai,
Maharashtra 421503

2. Database Users
• Naive users-who interact with the system by invoking one of the
application programs
• Application programmers-computer professionals who write application
programs. Application programmers .
• Sophisticated users -interact with the system without writing programs.
Instead, they form their requests in a database query language.
• Specialized users- who write specialized database applications that do not
fit into the traditional data-processing framework.
• database administrator (DBA)- A person who has such central control over
the system .

3. Levels of abstraction in a DBMS
• Physical Level-“How” the data are actually stored.
• Logical Level-what relationships exist among those data
• View Level-highest level of data Abstracts

5. DBMS Architecture

6. 1-Tier Architecture
• User Interface
• The 1-Tier
architecture is used
for development of
the local application,
where programmers
can directly
communicate with
the database for the
quick response.

7. 2-Tier Architecture
• client-server architecture
• client can directly
communicate with the
database
• For this interaction, API's
like: ODBC(open database
connectivity)

9. 3-Tier Architecture
• used web application.
• Client/External Level/View Level
• Web Server/Conceptual Level/Logical level
• Database Server/Internal Level/Physical Level

10. External level
 Highest or Top level of data abstraction ( No knowledge of DBMS S/W and H/W
or physical storage).
 This level is concerned with the user.
 Each external schema describes the part of the database that a particular user is
interested in and hides the rest of the database from user.
 There can be n number of external views for database where n is the number
of users.
 For example, a accounts department may only be interested in the student fee
details. It would not be expected to have any interest in the personal
information about students.
 All database users work on external level of Dbms .

11. Conceptual Level
• This level is in between the user level and physical storage view.
• There is only one conceptual view for single database.
• It hides the details of physical storage structures and concentrates on
describing entities, data types, relationships, user operations, and
constraints.

12. Internal Level
• It is the lowest level of data abstraction. (it has the knowledge about s/w and h/w)
• At this level, it keeps the information about the actual representation of the entire database i.e.
the actual storage of the data on the disk in the form of records or blocks.
• It is close to the physical storage method.
• The internal view is the view that tells us what data is stored in the database and how. At least
the following aspects are considered at this level: Storage allocation, Access paths etc.
• The internal view does not deal with the physical devices directly. Instead it views a physical
device as a collection of physical pages and allocates space in terms of logical pages.

13. Level of DBMS Architecture :

14. Example: University Database
Course_info(cid:string,cname:string)
 Students(sid: string
name: string,
login: string,
age: integer)
 Courses(cid: string,
cname:string,
credits:integer)
 Enrolled(Eid:string,
cid:string,
grade:string)
 Relations stored as unordered files.
 Index on first column of Students.
 Conceptual schema:
 Physical schema:
student_info(cid:string, name:string)
 External Schema (View 1 ):
 External Schema (View 2):

15. External view 2 (COBOL)
01 EMPC.
02 EMPNO PIC X(6).
02 DEPTNO PIC X(4).
Internal STORED_EMP BYTES=20
PREFIX
EMP#
DEPT#
PAY
BYTE=6 , OFFSET=0
BYTE=6, OFFSET=6, INDEX=EMPX
BYTES=4, OFFSET=12
BYTES= 4, ALIGN= FULLWORD,OFFSET=16
External view 1 (C++)
DCL 1 EMPP,
2 EMP# CHAR(6)
2 SAL FIXEDBIN(31)
Example: employee database
Conceptual
EMPLOYEE
EMPLOYEE_NUMBER CHARACTER(6)
DEPARTMENT_NUMBER CHARACTER(6)
SALARY DECIMAL(5)

16. Three Levels of Architecture
B_noE_no F_name L_name Age Salary
Empl_No F_name L_name DOB Salary Branch_No
Conceptual level
Internal level
struct EMPLOYEE {
int Empl_No;
int Branch_No;
char F_name [15];
char L_name [15];
struct date Date_of_Birth;
float Salary;
struct EMPLOYEE *next; //pointer to next employee record
}; index Empl_No; index Branch_No; //define indexes for
employees
Syntax Example:
External view 1 External view 2
Empl_No L_name

17. Data independence
• Data independence is the capacity to change the schema at one level
without having to change the schema at the next higher level
• Two types of data independence are
• Logical data independence
• Physical data independence

18. Logical data independence
• Whenever, there is a change or modification at the
conceptual level without affecting the user level or external
level, it is known as logical data independence.
E.g. The name field in conceptual view is stored as first name,
middle name and last name whereas in external view, it remains
to be as a single name field.

19. Physical data independence
• Whenever, the changes are made at the internal level without
affecting the above layers, it is known as physical data
independence.
• E.g. The location of the database, if changed from C drive to D
drive will not affect the conceptual view or external view as the
commands are independent of the location of the database.

21. Database users and user interfaces
• Naive Users
• Application Programmers
• Sophisticated Users
• Specialized Users
• DBA

22. Responsibilities of DBA
• Installation, configuration and upgrading of Database server software and related products.
• Evaluate Database features and Database related products.
• Establish and maintain sound backup and recovery policies and procedures.
• Take care of the Database design and implementation.
• Implement and maintain database security (create and maintain users and roles, assign
privileges).
• Database tuning and performance monitoring.
• Application tuning and performance monitoring.
• Setup and maintain documentation and standards.
• Plan growth and changes (capacity planning).
• Work as part of a team and provide 24x7 support when required.
• Do general technical troubleshooting and give cons.
• Database recovery.

23. Storage manager
• The storage manager is important because databases typically require
a large amount of storage space.
• Storage Manager Components:
• Authorization and integrity manager which tests for the satisfaction of
integrity constraints and checks the authority of users to access data.
• Transaction manager which ensures that the database itself remains
in a consistent state despite system failures, and that concurrent
transaction executions proceed without conflicting.

24. • File manager: which manages the allocation of space on disk storage
and the data structures used to represent information stored on disk.
• Buffer manager which is responsible for fetching data from disk
storage into main memory. Storage manager implements several data
structures as part of the physical system implementation. Data files
are used to store the database itself. Data dictionary is used to stores
metadata about the structure of the database, in particular the
schema of the database.

25. Query processor
• The query processor also very important because it helps the
database system simplify and facilitate access to data. So quick
processing of updates and queries is important.

26. Query Processor Components:
• DDL interpreter: It interprets DDL statements and records the
definitions in the data dictionary.
• DML compiler: It translates DML statements in a query language into
an evaluation plan consisting of low-level instructions that the query
evaluation engine understands.
• Query evaluation engine: It executes low-level instructions generated
by the DML compiler.

27. DBMS Functions-
• Data Dictionary Management
• Data Storage Management
• Data transformation and Presentation
• Security Management
• Multiple Access Control
• Backup and Recovery Management
• Data Integrity Management
• Database Access Languages
• Databases Communication Interfaces

28. Database Administrator(DBA)
• One of the main reasons for using DBMSs is to have central control of
both the data and the programs that access those data. A person who
has such central control over the system is called a database
administrator (DBA).

29. Responsibilities of DBA
• Software installation and Maintenance
• Data Extraction, Transformation, and Loading
• Database Backup and Recovery
• Performance Monitoring
• Security
• authentication