Centralized and Client/Server
Architecture and Classification of
DBMS
Prepared By :
Topic To be Covered
Classification of DBMSs,
Data modelling using the Entity-relationship model(ER)
Centralized and Client-Server Architectures
•
Centralized DBMS: combines everything into single
system including- DBMS software, hardware, application
programs and user interface processing software.
Basic Client-Server Architectures
A server is a system containing both hardware and software that can provide
services to the client machines, such as file access, printing or database access.
In general, the client/server architecture was developed to deal with computing
environment in which large number of PCs, workstation, file server, printers,
database server, web servers, and other equipment are connected via a network.
The idea is to define
Specialized Servers
with specific functionality.
For example, it is possible to connect a number of PCs or workstation as client to
the file server that maintain the files of the client machine.
Similarly, Printer Server dedicated to all the print requests forwarded to this
machine.
In this way, resources provided by the specialized servers can be accessed by
many client machines.
The client machines provide the user with the appropriate interface to utilize these
servers.
Specialized Servers with Specialized functions:
• File Servers • Printer Servers • Web Servers • E-mail Servers
Clients:
•
Provide appropriate interfaces and a client-version of
the system to access and utilize the server resources.
•
Clients maybe 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.)
Logical two-tier client/server architecture
DBMS Server
•
Provides database query and transaction services to
the clients
•
Sometimes called query and transaction servers
Diskless node
A diskless node (or diskless workstation) is a workstation or personal computer
without disk drives, which employs network booting to load its operating system
from a server. (A computer may also be said to act as a diskless node, if its disks are
unused and network booting is used.)
Diskless workstation
Alternatively referred to as a diskless node, dummy terminal, or dumb terminal,
a diskless workstation is a networked computer that provides no local hard
drive space or floppy disk drive access. These terminals will have
a monitor, motherboard, network card, keyboard, and mouse. This term can also be
used to describe any computer that has a hard drive, but is booting and using
Two Tier Client-Server Architecture
In client/server architecture User Interface Program and Application programs can run on the client side.
When DBMS access is required, the program establish a connection to the DBMS(which is on the server side); once the connection is created, the client program can communicate with the DBMS.
A standard called Open Database Connectivity (ODBC) provide an application program interface(API), which allows client-side programs to call the DBMS, as long as both client and server machines have the necessary software installed.
Similarly a related standard is used for the Java Programming language (JDBC), has also been defined. This allow Java client program to access the DBMS through a standard interface.
the architecture is called two tier architecture because the software components are distributed over two system.
Two Tier Client-Server Architecture
•
A client program may connect to several DBMSs.
•
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. In such situations the
server may be called the
Data Server
.
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Three tier Architecture
Many web applications use an architecture called the application server which add an intermediate layer between the client and the database server.
Intermediate Layer called Application Server or Web Server:
The intermediate layer or the middle tier is sometimes called the application server and sometimes the Web Server.
Three tier Architecture
Additional Features- Security:
Improve database security by checking clients credentials before forwarding the request.
•
encrypt the data at the server before transmission
Logical three-tier client/server architecture.
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Classification of DBMSs
Several criteria are normally used to classify DBMSs. Data model
Number of users
Number of sites
Cost
Types of access path
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Classification of Data Model
Relational model represents a database as a collection of tables, where each table can be stored as a separate file.
Object model defines a database in terms of objects, their properties, and their operations. Relational DBMSs have been extending their models to incorporate object database
concepts and other capabilities; Object-relational model Hierarchical model represents data as record types
and also represents a limited type of l:N relationship, called a set type.
Network model represents data as hierarchical tree structures.
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Hierarchical DBMS
Represent data as hierarchical tree structures
Each hierarchy represents a number of related records
A hierarchical database model is a data model in which the data is organized into a tree-like structure. The structure allows representing information using parent/child
Network DBMS
Resembles hierarchical model Represent data as record types
Collection of records in 1:N relationships
The schema of Figure 2.1 in network model
notation
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Relational DBMS
Relational DBMS (cont.)
Relational schema
representation of relational database’s entities, attributes within those entities, and relationships between those entities
Relational table
Object Oriented Model
Represent database in terms of object, their properties and their operations. Objects with same structure and behavior belongs to same class.
Classes are organized into hierarchies.
Object relational DBMS
Number of users
Single-user systems support only one user at a time and are mostly used with personal computers.
Multiuser systems, which include the majority of DBMSs, support multiple users concurrently.
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Number of sites
A DBMS is centralized if the data is stored at a single computer site.
A distributed DBMS (DDBMS) can have the actual database and DBMS software distributed over many sites, connected by a computer network.
Homogeneous
Heterogeneous
Federated or Multidatabase Systems
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Types of the access path
One well-known family of DBMSs is based on inverted file structures. Finally, a DBMS can be general purpose or special purpose.
Online transaction processing (OLTP) systems,
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