1. Database Systems
LECTURE #:05
FACULTY OF CS & IT
UNIVERSITY PROGRAMM

2. Three-Schema Architecture
(cont’d)
 Mappings among schema levels are needed
to transform requests and data.
 Programs refer to an external schema,
and are mapped by the DBMS to the
internal schema for execution.
 Data extracted from the internal DBMS
level is reformatted to match the user’s
external view (e.g. formatting the results
of an SQL query for display in a Web
page)

3. Mappings
 There are two levels of mapping in the architecture
 Conceptual/internal mapping defines the
correspondence between the conceptual view and
the stored database
 An external/conceptual mapping defines the
correspondence between a particular external view
and the conceptual view

4. 4

5. DBMS Languages
 Data Definition Language (DDL)
 Data Manipulation Language (DML)
 Data Control Language (DCL)
 High-Level or Non-procedural
Languages: These include the relational
language SQL.

6. DBMS Languages (cont’d)
 Data Definition Language (DDL):
 Used by the DBA and database designers to specify the conceptual
schema of a database.
 In many DBMSs, the DDL is also used to define internal and
external schemas (views).
 Data Manipulation Language (DML):
 Used by the DBA for manipulation of records
 Insertion,Updation ,Deletion and retrieval of record.
 SELECT
 INSERT
 UPDATE
 DELETE

7. Data Control Language (DCL)
 A Data Control Language (DCL):
 DCL is a subset of SQL, used to control access to data
in a database.
 Examples of DCL commands include:
 GRANT to allow specified users to perform specified tasks.
 REVOKE to cancel previously granted or denied permissions.
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8. Host Language
 A domain-specific language (DSL)
 DSL is an Application Programming Interface
(either a Programming Language or executable
Specification Language?) whose grammar matches
the Problem Domain.
 The biggest, most common example here is Structured
Query Language. It provides a declarative syntax, and
you call it from an Object Oriented application that uses
a procedural syntax.
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9. Role of Database Administrator
 Defining the conceptual schema
 Defining the internal schema
 Liaising with users
 Defining security and integrity rules
 Defining backup and recovery procedures

10. Basic 2-tier Client-Server
Architectures
 Specialized Servers with Specialized
functions
 Print server
 File server
 DBMS server
 Web server
 Email server
 Clients can access the specialized servers
as needed by the applications

11. Client/Server applications
 Applications can be divided into categories:
 First, user-written applications. (regular
application programs, written language
such as C or Java.
 Second, vendor-provided applications
(often called tools). The overall purpose
of such tools is to assist in the process to
creating and executing other applications.

12. Logical two-tier client server
architecture

13. Two Tier Client-Server
Architecture
 A client program may connect to several
DBMSs, sometimes called the data sources.
 In general, data sources can be files or other
non-DBMS software that manages data.
 Other variations of clients are possible: e.g.,
in some DBMSs, more functionality is
transferred to clients including data
dictionary functions, optimization and
recovery across multiple servers, etc.

14. Clients
 Provide appropriate interfaces through a
client software module to access and utilize
the various server resources.
 Clients may be diskless machines or PCs or
Workstations with disks with only the client
software installed.
 Connected to the servers via some form of a
network.
 (LAN: local area network, wireless
network, etc.)

15. DBMS Server
 Provides database query and transaction services
to the clients
 Relational DBMS servers are often called SQL
servers, query servers, or transaction servers
 Applications running on clients utilize an
Application Program Interface (API) to access
server databases via standard interface such as:
 ODBC: Open Database Connectivity standard
 JDBC: for Java programming access
 Client and server must install appropriate client
module and server module software for ODBC or
JDBC

16. Client/Server Architecture
 One client one Server (1:1)
 Clients and Server running on different
machines
 Components:
 End User
 Clients
 Server
 Database
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17. Client/Server Architecture
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18. Centralized Architecture
 One Server many Clients (1:M)
 End Users
 Client Machines
 Communication Networks
 Server Machine
 Database
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19. Centralized Architecture
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20. Centralized DBMS Architectures
 Centralized DBMS:
 Combines everything into single system
including- DBMS software, hardware,
application programs, and user interface
processing software.
 User can still connect through a remote
terminal – however, all processing is
done at centralized site.

21. Distributed Processing
 Distinct machines can be connected
together into a communications network
 The term "parallel processing" is also
sometimes used with essentially the same
meaning

22. Distributed Architecture
 Many Server many Clients (M:M)
 Used at enterprise level
 Each machine runs both clients and server
 Data is spread across many machines
 Application sometime needs the ability to access data from
more than one machines
 Such access in two different ways:
 A client be able to access any number of server but only one at a
time
 The client might be able to access many servers simultaneously.
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23. Distributed Architecture
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24. Three Tier Client-Server
Architecture
 Common for Web applications
 Intermediate Layer called Application Server or Web
Server:
 Stores the web connectivity software and the business logic
part of the application used to access the corresponding data
from the database server
 Three-tier Architecture Can Enhance Security:
 Database server only accessible via middle tier
 Clients cannot directly access database server