Chapter 6: Client/Server and Intranet Computing

1
Chapter 6Client/Server and Intranet Computing

• Business Data Communications, 6e

2
What is Client/Server?

• Client
• Server
• Network
• How is client/server different from other
  distributed computing?
• Heavy reliance on user-friendly applications
• Emphasis on centralizing databases and management
  functions
• Commitment to openness/modularity
• Networking fundamental to operation

3
Client/Server Terminology

• Application Programming Interface (API) A set of
  function and call programs that allow clients and
  servers to intercommunicate.
• Client A networked information requester
  (usually a PC or workstation) that can query a
  database and/or other information from a server.
• Middleware A set of drivers, APIs, or other
  software that improves connectivity between a
  client application and a server.
• Relational Database A database in which
  information access is limited to the selection of
  rows that satisfy all search criteria.
• Server A computer, usually a high-powered
  workstation or a mainframe, that houses
  information for manipulation by networked
  clients.
• Structured Query Language (SQL) A language
  developed by IBM and standardized by ANSI for
  addressing, creating, updating, or querying
  relational databases.

4
Client-Server Environment
5
Why is Client-Server Different?

• Emphasis on user-friendly client applications
• Focus on access to centralized databases
• Commitment to open and modular applications
• Networking is fundamental to the organization

6
Client/Server Applications

• Emphasis on GUI for users
• Database Example
• Database on server, applications for access on
  client, glue (like SQL) enables requests)
• Application logic can be client-only, or split
  between client and server

7
Classes of Client-Server Applications

• Host-based processing
• Server-based processing
• Client-based processing
• Cooperative processing
• Thick client vs Thin server

8
3-Tier Client/Server Architecture
9
Middleware

• Standardized interfaces and protocols between
  clients and back-end databases
• Hides complexity of data sources from the
  end-user
• Compatible with a range of client and server
  options
• All applications operate over a uniform
  applications programming interface (API).

10
Middleware Architecture
11
Logical View of Middleware
12
Basic Message Passing Primitives
13
Message Passing Issues

• Reliability vs Unreliability
• Reliable facilities guarantee delivery, provide
  error-checking, retransmission, etc
• Alternatively, the message can be sent without
  success/failure reduces complexity and overhead,
  passes responsibility for confirmation to
  application
• Blocking vs Nonblocking
• Non-blocking more efficient, but difficult to
  test and debug programs
• Blocking (synchronous) retains control until
  acknowledgment is received

14
Remote Procedure Call Mechanism
15
Client/Server Binding

• Nonpersistent binding
• Does not maintain state information, connections
  re-established as necessary
• Inappropriate for RPCs used frequently by same
  caller
• Persistent binding
• Connection sustained until procedure return
• Useful for applications making repeated calls to
  remote procedures

16
Object-Oriented Mechanisms

• Clients and servers ship messages between
  objects.
• May rely on an underlying message or RPC
  structure or be developed directly on top of
  object-oriented capabilities in the operating
  system
• Success depends on standardization of the object
  mechanism, but competing models exist
• COM, OLE, CORBA

17
Intranets

• Implementation of Internet-based technologies
  within an organization, rather than for global
  connectivity
• Immensely successful in corporate computing
  contexts

18
Advantages of Intranets

• Rapid prototyping
• Scales effectively
• Little training required
• Can be implemented on variety of systems
• Open architecture allows interaction across
  platforms

• Supports a range of distributed servers
• Allows integration of legacy systems on client
  and server side
• Supports a range of media types
• Inexpensive to implement

19
The Intranet Web

• Web Content
• The web can be used to effectively distribute
  content in a way that requires no new training
  for end-users
• Web/Database Connectivity
• Multiple tools exist to serve as middleware
  between web servers and data sources
• Electronic Mail
• Network News

20
Corporate Intranet Example
21
Web/Database Connectivity

• Advantages
• Ease of administration
• Deployment
• Development speed
• Flexible information presentation

• Disadvantages
• Limited functionality
• Stateless operation makes tracking difficult

22
Intranet Webs vs Traditional Client/Server

• Client/Server Disadvantages Include1. Long
  development cycles2. Difficulty in partitioning
  applications, and modifying based on user
  feedback3. Effort in distributing upgrades to
  clients4. Difficult in scaling servers to
  respond to increased load5. Continuous
  requirement for more powerful desktop machines

23
Other Intranet Technologies

• Electronic Mail
• Closed internal mail systems (delivery
  verification, etc)
• Internal mailing lists
• Network news (USENET)
• Can be adopted for internal intranet uses

24
Extranets

• Extends the intranet concept to provide
  information and services to selected outside
  populations, such as customers and suppliers
• Enables the sharing of information between
  companies
• A TCP/IP enabled form of EDI

25
Advantages of Extranets

• Reduced costs
• Coordination
• Customer Satisfaction
• Expedited communication

26
Methods for Converting Intranets to Extranets

• Long-distance dial-up access
• Internet access to intranet with security
• Internet access to an external server that
  duplicates some of a companys intranet data
• Internet access to an external server that
  originates database queries to internal servers
• Virtual private network

27
Service Oriented Architecture

• Client/server architecture utilized widely by
  enterprise systems
• Business functions consist of modular structures

28
SOA Architectural Elements

• Service provider network node that provides a
  service interface for a software asset that
  manages a specific set of tasks.
• Service requestor network node that discovers
  and invokes other software services.
• Service broker specific kind of service provider
  that acts as a registry and allows lookup of
  service provider interfaces and service locations.

29
Key Characterisitics for Effective Services Use

• Coarse-grained
• Interface-based design
• Discoverable
• Single Instance
• Loosely Coupled
• Asynchronous

30
SOA Example