PPT Lecture 1.3 Database System Administrator.pptx

Department of Computer Science and Engineering (CSE)
University Institute of Engineering (UIE)
OBJECTIVES
At the completion of this Chapter , students should be
able to do the following:
• Understand DBMS Architecture
• Appreciate the evolution of ANSI SPARC (3 level
architecture)

Introduction
ANSI
American National Standards Institute
SPARC
Standards Planning And Requirements Committee
• It is an abstract design standard for a Database Management
System (DBMS), first proposed in 1975.

Three-level architecture
• External level
• Conceptual level
• Internal level
• The Three Level Architecture has the aim of enabling users to
access the same data but with a personalized view of it. The
distancing of the internal level from the external level means that
users do not need to know how the data is physically stored in
the database. This level separation also allows the Database
Administrator (DBA) to change the database storage structures
without affecting the users' views.

Three-level architecture
• External Level (User Views): A user's view of the database describes
a part of the database that is relevant to a particular user. It excludes
irrelevant data as well as data which the user is not authorized to
access.
• Conceptual Level: The conceptual level is a way of describing
what data is stored within the whole database and how the data is
inter-related. The conceptual level does not specify how the data is
physically stored.
• Internal Level: The internal level involves how the database is
physically represented on the computer system. It describes how
the data is actually stored in the database and on the computer
hardware.

Objective of the three-level
architecture
• It allows independent customized user views: Each user should be
able to access the same data, but have a different customized view
of the data. These should be independent: changes to one view
should not affect others.
• It hides the physical storage details from users: Users should
not have to deal with physical database storage details.
• The database administrator should be able to change the
database storage structures without affecting the users’ views.
• The internal structure of the database should be unaffected by
changes to the physical aspects of the storage: For example, a
changeover to a new disk.

Database schemas
There are three different types of schema corresponding to the three
levels in the ANSI-SPARC architecture.
Schema is the structure of the database that defines the objects in the
database
• The external schemas describe the different external views
of the data and there may be many external schemas for a
given database.
• The conceptual schema describes all the data items and
relationships between them, together with integrity constraints
(later). There is only one conceptual schema per database.
• The internal schema at the lowest level contains definitions
of the stored records, the methods of representation, the
data fields, and indexes. There is only one internal schema
per database.

Department of Computer Science and Engineering
(CSE)
The
way
users
perceiv
e the
data.
The way the
DBMS and OS
perceive the
data.

Mapping between views
• Three view-levels are described by means of three schemas.
• These schemas are stored in the data dictionary.
• In DBMS, each user refers only to its own external schema.
• Hence, the DBMS must transform a request on. a specified
external schema into a request against conceptual schema,
and then into a request against internal schema to store and
retrieve data to and from the database.
• The process to convert a request (from external level) and the
result between view levels is called mapping.
• The mapping defines the correspondence between three view
levels.
• The mapping description is also stored in data dictionary.
• The DBMS is responsible for mapping between these three
types of schemas.

Mapping between views
There are two types of mapping.
(i) External-Conceptual mapping
• An external-conceptual mapping defines the correspondence between a
particular
external view and the conceptual view.
• The external-conceptual mapping tells the DBMS which objects on the
conceptual level correspond to the objects requested on a particular user's
external view.
• If changes are made to either an external view or conceptual view, then
mapping must be changed accordingly.
(ii) Conceptual-Internal mapping
• The conceptual-internal mapping defines the correspondence between the
conceptual view and the internal view, i.e. database stored on the physical
storage device.
• It describes how conceptual records are stored and retrieved to and
from the storage device.

Example

Data Independence
• The ability to modify a scheme definition in one level without
affecting a scheme definition in a higher level is called data
independence.
There are two kinds:
• Logical data independence
• Physical data independence

Data Independence
Logical data independence
• The ability to modify the conceptual scheme without causing
application programs to be rewritten.
• Immunity of external schemas to changes in the conceptual schema.
• The change would be absorbed by mapping
between external and conceptual levels.
Physical data independence
• The ability to modify the internal scheme or physical storage
structures and devices without affecting conceptual or external
schemas .
• Modifications at this level are usually to improve performance.
Logical data independence is difficult to achieve than
physical data independence.

Database Administrator (DBA)
• A database administrator (DBA) is an IT professional responsible for
the installation, configuration, upgrading, administration, monitoring,
maintenance, and security of databases in an organization.

Responsibilities of DBA
Makes decisions concerning the content of the database.
✔ Identify the entities of interest to the enterprise
and to identify
information to be recorded about those entities
Plans storage structures and access strategies.
✔ How the data is to be represented in the database.
✔ Specify the representation by writing the storage structure definition
(using the internal data definition language).
✔ The associated mapping between the storage structure definition and the
conceptual schema must also be specified.
Provides support to users.
✔ Ensure that the data users require is available,
and to write the necessary external schemas.
✔ The mapping between any given eA1ernal schema and the conceptual'
schema must also be specified.

Responsibilities of DBA
Defines security and integrity checks.
✔ Providing the authorization and authentication checks such
that no
malicious users can access database and it must remain protected.
✔ DBA must also ensure the integrity of the database.
Interprets backup and recovery strategies.
✔ Define and implement an appropriate recovery
strategy to recover he
database from all types of failures.
Monitoring performance and responding to changes in
requirements.
✔ DBA is responsible for so organizing the system as to get the
performance that is "best for the enterprise," and for making the
appropriate adjustments as requirements change.

Outcomes
• Analyze an information storage problem and derive an
information model expressed in the form of an entity
relation diagram and other optional analysis forms,
such as a data dictionary.
• Demonstrate an understanding of the relational data
model.
• Appreciate the roles & responsibilities of DBA.

References
• Database System Concepts by Abraham
Silberschatz
• Database System Concepts by
Sudarshan, Korth Education)
(McGraw-
Hill
• Fundamentals of Database SystemBy Elmasari
&Navathe- Pearson Education
• http://ecomputernotes.com/database-system/rdbms
• https://www.tutorialspoint.com/sql/sql-rdbms-concepts.htm
• https://www.studytonight.com/dbms/rdbms-concept

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