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Chapter 7: Client/Server Computing. Business Data Communications, 5e. 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 - PowerPoint PPT Presentation
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Chapter 7:Client/Server Computing
Business Data Communications, 5e
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
Client-Server Environment
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
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
Classes of Client-Server Applications
• Host-based processing
• Server-based processing
• Client-based processing
• Cooperative processing
• “Fat client” vs “fat server”
3-Tier Client/Server Architecture
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).
Middleware Architecture
Logical View of Middleware
Basic Message Passing Primitives
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
Remote Procedure Call Mechanism
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
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
Intranets
• Implementation of internet-based client/server technology within an organization, rather than for global connectivity
• Immensely successful in corporate computing contexts
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
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
Web/Database Connectivity
• Advantages– Ease of administration
– Deployment
– Development speed
– Flexible information presentation
• Disadvantages– Limited functionality
– Stateless operation makes tracking difficult
Intranet Disadvantages
• Long development cycles• Difficulty in partitioning applications, and
modifying based on user feedback• Effort in distributing upgrades to clients• Difficult in scaling servers to respond to
increased load• Continuous requirement for more powerful
desktop machines
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
The Extranet Web
• 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
Advantages of Extranets
• Reduced costs
• More marketable products
• Increased productivity
• Enhanced profits
• Reduced inventories
• Faster time to market
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 company’s intranet data• Internet access to an external server that
originates database queries to internal servers• Virtual private network
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