1 PROJECT Web-based Database Applications Lecture 3: Client/Server Databases Environment

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PROJECTWeb-based Database Applications

Lecture 3: Client/Server Databases Environment

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CLIENT/SERVER

ARCHITECTURE

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Evolution of DBMSs - Modeling

Flat-file system Often text files for sequential access

Relational Database Management System (RDBMS) Informix, Oracle, Sybase, DB2, etc.

Object-oriented Database Management System (OODBMS) Gemstone, O2, ObjectStore, Matisse, Jasmine,

Versant, etc. Object-relational Database Management System

(ORDBMS) Informix, Oracle, DB2, Illustra, UniSQL, Matisse, etc.

© H. Afsarmansesh, 2003

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Stand-alone to Network-based DBs Centralized DBs

Stand-alone, on a mainframe or workstations e.g. Manufacturing industry, SMEs

Distributed DBs Network-based Supporting geographic dispersion of sites

e.g. Banking, Service provision industry

Federated DBsNetwork-based Supporting heterogeneity & autonomy of sites

e.g. Virtual organizations, Virtual Laboratories

Evolution of DB system - Architecture


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Mainframe-based environment All applications run directly on the main system

Client/Server environment Operates in networked environments Splits the processing of an application between:

A Front-end Client A Back-end Processor (server)

Client process requires some resources that the server provides

Clients and servers can reside on the same computer, or locate on different computers in the network

Client and Server are intelligent and programmable

Evolution of multi-user DB environment


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Designing the DB architecture and environment

Good balance between Centralization & Distribution

Mainframe-based or Client/Server based databases

Client/Server architecturesClient/Server architectures

1- File Server architecture

2- Database Server (two-tier) architecture

3- three-tier architecture

Hoffer © Prentice Hall, 2002

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Client/Server Systems

A networked computing model (with LAN / WAN)

Processes distributed between clients and servers

ClientClient – application running on a workstation or a PC, that requests and uses a service

ServerServer – application running on a computer (PC/mini/mainframe), that provides a service

Client/server architectures differ in their distribution of Application Logic components across clients and servers


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Application Logic in Client/Server Systems

Presentation Logic component Input – keyboard/mouse Output – monitor/printer

Processing Logic component I/O processing Business rules (validity checks) Managing Data

Storage Logic component Data storage Data retrieval

GUI InterfaceGUI Interface

Procedures, functions,Procedures, functions,programsprograms

DBMS actionsDBMS actions


Application Logic consists of 3 components

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1- File server (two-tier) architecture

File server is a device that manages file operations and is shared by each of the client PCs attached to the LAN / WAN

LAN/WAN

FAT FAT CLIENTCLIENT


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Limitations of file server architecture

Network is a bottleneck – high traffic load Tight-coupling among the application and the data Considerable processing burden on the client PC Large memory for the client PC (full DBMS transferred!) For multi-user environments - Expert application

programmers are needed Request to set locks for shared data(base) integrity Understand and consider how their application affects the

concurrency, recovery and security of the shared data(base)

Handling shared data(base) problems becomes the responsibility of the application program


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2- Database server (two-tier) architecture

Database server is a computer responsible for database storage access and processing, constituting a 2-tier client/server architecture

LAN/WAN


Database

Server

Selected

Thinner Thinner CLIENT CLIENT

Fatter DB Fatter DB SERVERSERVER

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Advantages of two-tier database architecture

Data traffic load is reduced

Thinner Client: Processing power only required at the Database server Authorization, integrity, query/update only at Database

server

Fatter Server: Processing power and larger memory in one location Stored proceduresStored procedures can be defined and run at Database

server A piece of code in the DBMS language (e.g. Oracle’s PL/SQL) Creates DBMS dependency Decreased performance


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Two-Tier Database Server Architecture – 2 layers2 layers

Stored procedures:Stored procedures: Reduce the network

traffic Improve security Improve data integrity

Connolly © Addison Wesley, 2002

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3- Three-tier Database architecture

A Client/server configuration that includes: client layer, application layer (also called application server) and database server layer

LAN/WAN


Database

Server

Thin Thin CLIENTCLIENT

Application

Server

Client layer

Application layer

DB server layer

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Three-Tier Database Architecture - 3 layers3 layers

Client Client only performs a little processing with limited or no data storage

Application serverApplication server performs the data processing and applies the business rules

Database serverDatabase server performs the data validation & data access

Database connectivity provides a link between the application logic and the DBMS

A. Benabdelkader ©UvA, 2002/2003

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Advantages of 3-tier compared to 2-tier

3-tier architecture is a popular choice for Internet applications and Net-centric information systems

The architecture provides an increased level of: Scalability

The load between layers can be measured and adjusted

Flexibility /Reusability Loose coupling among the data and application Less reliance on proprietary DBMS languages Easier to change the DBMS

Performance / Reduced risks Lower load on client and division of load between the application

layer and the server layer

Lower long term costs For maintenance and changes in the configuration


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Client/Server Architecture - Types of ClientsTypes of Clients

Fat clientsFat clients Client does most of the work Relatively large and complex Responsible for user interfaces, application

logic and many of the DBMS functions

Thin clientsThin clients Client is simple and light A PC configured for handling user interfaces Limited storage


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Partitioning a Database application There is no one optimal client/server architecture no one optimal client/server architecture

solutionsolution for all database applications A main goal is to reach better performance and better performance and

interoperabilityinteroperability Decisions must be made about the placement of the placement of the

processing logicprocessing logic How to partition the environment into two-, three-, two-, three-,

or n-tier architectureor n-tier architecture

In each case, storage logic is always handled by the DB server, and the presentation logic by the Client

Client/Server Architecture – Application partitioningApplication partitioning


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WEB-DATABASES

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Data on the Web sites

Many Web sites are file-based, where each Web document is stored in a separate file

For large sites, this can lead to significant data management problems

Also many Web sites now contain more dynamic information, e.g. products and pricing data

Maintaining updated data in both a database and separate static HTML files is problematic

Accessing database directly from Web would be a better approach


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Management of data at Web servers

Static Web page is an HTML documents stored in a file

Content of a dynamic Web page is generated each time it is accessed Can respond to user input from browser Can be customized for each user Hypertext formatting of the page is used by the

server to generate it Needs scripts that perform conversions from

different data formats (of the databse) into the HTML ‘on-the-fly’


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Web-Databases (or Web-based databases)

Web-databases are structured information repositories that can dynamically interact with a Web Server Web-databases allow for storing data content, in a

Web-structured format and let user publish information on the web

Web-databases provide a set of high-level functionality tools that support the development, maintenance, and deployment of applications with relative ease and speed

A. Benabdelkader ©UvA, 2002 /2003

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Advantages of Web-Databases

DBMS support data structure, security for access, query languages,

etc. Platform independence Standardization

through standard database connectivity layers Open-architecture that allows interoperability with a

variety of systems and technologies. Cost-effective solution that allows for scalability,

growth, and changes in strategic directions, and helps reduce applications development costs

…


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Disadvantages of Web-Databases

Reliability / Availability Web Security Immaturity of development tools Performance / load balancing Statelessness

Statelessness - no information about transactions is maintained on the server (cookies can be used if necessary)

Maintaining State - server tracks the state, e.g.

location, selections made, user information


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Web-Databases Applications

Catalogs Directories (e.g. Yellow pages) Online-Shopping Online Auctions Training courses Resource libraries Surveys Financial Analysis …


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Approaches to Integrate Web and DBMSs

Client/server architecture development, using:Client/server architecture development, using:

Java, JDBC, SQLJ, Servlets, and JSP Common Gateway Interface (CGI) Extending the Web Server

e.g. database request handling middleware Microsoft Web Solution Platform

ASP and ADO …


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Two-tier vs. three-tier architectures

Presentation Logic & Processing Logic

(Java, JavaScript, ActiveX, plug-ins, etc)

Processing Logic WebServer

(CGI, HTTP server API, HTTP server module,

etc.)

Storage Logic

DBMSTier 2

Presentation Logic Web browser

Presentation Logic & Processing Logic

(Java, JavaScript, ActiveX, plug-ins, etc)

Tier 1

Tier 3

Tier 1

Tier 2

Storage Logic

DBMS

Storage Logic

Files


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Three-Tier Database Architecture

Three layers: Client (GUI interface, I/O

processing) the Browser

Application server (Business rules)

the Web Server

Database server (Data storage)

the DBMS


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Client/Server Database Environment

‘Thin’ client, requires less power/cost hardware at the client side

Application maintenance is centralized Easier to modify or replace one tier without

affecting the others Separating business logic from database functions,

makes it easier to implement load balancing Maps quite naturally to the Web environment …


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Advantages: Scalability Technological flexibility Long-term cost reduction Better match of systems to business needs Reduced risk

Challenges: High short-term costs Tools and training Incompatible standards Interaction with Legacy databases

C/S Database Environment – advantages/disadvantagesadvantages/disadvantages


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C/S Database Environment - MiddlewareMiddleware

Software which allows an application to interoperateinteroperate with other software

No need for programmer/user to understand and code low-level operations for interoperability and internal processing

Accomplished via Application Program InterfaceApplication Program Interface (API) utilities

The “glue”“glue” that holds different layers of the client/server applications together


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Classification of base tools/approaches to build MiddlewareClassification of base tools/approaches to build Middleware

Remote Procedure Calls (RPC) - synchronous / asynchronous Client makes calls to procedures running on remote

computers Similar to Remote Method Invocation (RMI)

Message-Oriented Middleware (MOM) Asynchronous calls between the client via message queues

Publish/Subscribe Push technology server publishes information, to

subscribed clients, when available Object Request Broker (ORB)

Object-oriented management of communications between clients and servers

SQL-oriented Data Access SQL-based Middleware between applications and database

servers Hoffer © Prentice Hall, 2002

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Types of Middleware access to DatabasesTypes of Middleware access to Databases

Application Program Interface (API) for Native Application Program Interface (API) for Native databasedatabase A set of operations to access/manipulate the data Efficient Application developers use APIs, and so do not need

to develop low level DB operations

ODBC & JDBCODBC & JDBC Provide database connectivity standards supported by

most popular databases Fast and have high flexibility Complexity in learning


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MANAGING WEBSITES

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WEB-DATABASE SECURITY

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Challenges in Managing Websites

Web-based systems Security Issues Prevent unauthorized access and malicious data destruction

User’s Privacy Issues Protect users’ privacy rights

Coping with the Rate-of-Change of Internet Technology Deal with rapid advances in technology


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An important inhibitor to the growth of e-commerce: lack of user’s confidence in the security of web-

transactions

Protection of sensitive information and preservation of user’s access rights, through the web-related database access

Risk assessment and regular monitoring & testing for intrusion

Even new software tools/techniques may break the security of the site

SecuritySecurity in Client/Server Database Environment


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Establishing Internet security

Firewall to limit external access to data

Routers to transmitand distribute message packets to correct destination

IDS to monitor and recognize security

breach attempts


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Website Security enablers

FirewallFirewall – hardware/software security component that limits the external access to company’s data

Proxy serverProxy server – firewall component that manages Internet traffic to and from a LAN

RouterRouter – intermediate device that transmits message packets to correct destination over most efficient pathway

Intrusion detection system (IDS)Intrusion detection system (IDS) – system that identifies attempt to hack or break into a system


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Network environments create multi-layer security issues

(Network, OS, Web-server, Database, Communication)(Network, OS, Web-server, Database, Communication)

1- Network-level security1- Network-level security create an account with a user name and passwordWeb server and DB server on separate LAN away from

other business systems

Minimize sharing of hard disks among servers

Regular monitoring of network and firewall logs

Install probe (attack)-monitor software

Variety of Security levels for C/S Environment -1


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2- Operating system-level security2- Operating system-level security


Patch (fix) all known OS vulnerabilities and look for new ones Install anti-virus software for: the system boot-time, file download time, and the email reception time, for virus detection Monitor server logs for unauthorized activity, e.g using IDS Intrusion detective system Disable non-required services to reduce risk of unauthorized access, e.g. sending automatic emails during an Internet access, that is allowed by the OS, should be disabled


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3- Web-server-level security3- Web-server-level securityVariety of Security levels for C/S Environment - 3

Restrict number of users on Web server- Give as few as possible “super users” and administrator rights

Restrict the access (minimize number of open ports) - http and https only, if possible

Remove unneeded programs that load automatically when setting up the server

- Delete demo programs that give hackers the access details

desired - Restrict CGI scripts (have security problems) to one

subdirectory For Unix, only install minimum software for Web server

- Do not boot the default OS that provides a lot of added functionality

Compilers should not be accessible through the path for internal access


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4- Database level security4- Database level security

Variety of Security levels for C/S Environment - 4

To restrict access/manipulations rights of users to the DBs. Login/Password check Creating user roles and privileges assigned to user roles Views Access, authorization, rights preservation Other measures:

- Extra check when executing user-defined procedures

- Asking extra information (Mother’s maiden name) © H. Afsarmansesh, 2003

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5- Data communication level security5- Data communication level security


TCP/IP is not a very secure protocol Encryption/decryption processes

- transforming readable (plain text) data into unreadable (ciphertext)

A standard encryption method is the Secure Socket Layer (SSL), that is used by the “https” (not with the http)Public key / Private keyAuthentication / bio-metric devices (finger-print, eye pictures,

voice recognition)Digital signature the Virtual Private Network (VPN)


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Anonymity vs. Security of Internet communication

Internet communication must be secure

& Internet communication must remain anonymous

Chat rooms E-mail Access to public data (web-pages)

Tracking devices installed on the servers for National security reasons (e.g. FBI’s email monitoring devices installed on email servers, Carnivor and DCS1000)

Advertisement agencies tracking down users access for their data collection purposes


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References to books

DATABASE SYSTEMS - A practical Approach to Design, Implementation, and Management, T. Connolly, C. Begg, Third Edition, Addison Wesley, 2002.

MODERN DATABASE MANAGEMENT, J. A. Hoffer, M. B. Prescott, F. R. McFadden, Sixth Edition, Prentice Hall, 2002.

Core SERVLETS and JAVASERVER PAGES, M. Hall, Java 2 Platform, Enterprise Edition Series, Prentice Hall 2002.

Documents

1 PROJECT Web-based Database Applications Lecture 3: Client/Server Databases Environment