Application Programming Interface (API) A set of function and call programs that allow clients and servers to inter- communicate Client A networked.

Chapter 9

Client/Server, Intranet, and Cloud Computing

Client/Server Terminology

Client-Server Environment

Client/Server Characteristics

Client/Server Architecture

Client/Server Architecture for Database Applications

Client/Server

Database Usage

Classes of Client/Server Applications

Three Level Architectural Client/Server Framework

Three-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)

The Role of Middleware in Client/Server Architecture

Logical View of Middleware

Middleware Mechanisms

Basic Message Passing Primitives

Message Passing IssuesReliability versus

Unreliability

Reliable facilities guarantee delivery if possible

Such a facility would make use of a reliable transport protocol or similar logic to perform error checking, acknowledgment, retransmission, and reordering of misordered messages

Blocking versus Nonblocking

Non-blocking is more efficient, but difficult to test and debug programs

Blocking (synchronous) retains control until acknowledgment is received

Remote Procedure Call Mechanism

RPC Flow

Client/Server Binding

Object-Oriented Mechanisms

Clients and servers ship messages back and forth between objectsMay rely on an underlying message or RPC structure or be developed directly on top of object-oriented capabilities in the operating systemSuccess depends on standardization of the object mechanismCompeting designs:

Microsoft’s Component Object Model (COM), the basis for Object Linking and Embedding (OLE)Common Object Request Broker Architecture (CORBA) developed by the Object Management Group

Supported by IBM, Apple, Sun

Intranets

Advantages of Intranets

Rapid prototyping

Scales effectively

Little training required

Can be implemented on a 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

Example Corporate Web Page Structure

Web/Database Connectivity

Web/Database Connectivity

AdvantagesEase of administrationDeploymentDevelopment speedFlexible information presentation

DisadvantagesLimited functionalityStateless operation makes tracking difficult

Intranet Webs Versus Traditional Client/Server

Extranets

Makes use of TCP/IP and their applications, especially the WebThe distinguishing feature is that it provides access to corporate resources by outside clients

This outside access can be through the Internet or through other data communications networks

Provides more extensive access to corporate resources, usually in a fashion that enforces a security policyTypical model of operation is client/server

Benefits of Extranets

Reduced costsMinimizes paperwork and human involvement

CoordinationCritical information can be made available so that quick decisions can be made

Customer satisfactionProvides more information about the current status of products and services

Expedited communicationIncreases the efficiency and effectiveness of communication

Methods for Converting Intranets to Extranets

Service Oriented Architecture (SOA) Model

Key Characteristics for Effective Use of Services

Example Use of SOA

Cloud Computing

NIST defines cloud computing as:

“A model for enabling ubiquitous, convenient, on-demand network access to a shared pool of configurable computing resources that can be

rapidly provisioned and released with minimal management effort or service provider

interaction. This cloud model promotes availability and is composed of five essential characteristics, three service models, and four deployment models.”

Cloud Computing Elements

Service Models

Deployment Models

Cloud Computing

Context

Cloud Computing Reference Architecture

NIST establishes a reference architecture described as follows:

“The NIST cloud computing reference architecture focuses on the requirements of ‘what’ cloud services provide, not a ‘how to’ design solution and implementation. The reference architecture is intended to facilitate the understanding of the operational intricacies in cloud computing. It does not represent the system architecture of a specific cloud computing system, instead it is a tool for describing, discussing, and developing a system-specific architecture using a common framework of reference.”

Reference Architecture Objectives

NIST Cloud Computing Reference Architecture

Figure 9.20 NIST Cloud Computing Reference Architecture

Summary The growth of

client/server computing Client/server

applications Database applications Classes of client/server

applications Three-tier client/server

architecture

Cloud computing Cloud computing elements Cloud computing reference

architecture

Chapter 9: Client/Server, Intranet, and Cloud Computing

Middleware Middleware architecture Message passing Remote procedure calls Object-oriented

mechanisms

Intranets Web content Web/Database applications Intranet Webs versus

traditional client/server

Service-oriented architecture

Extranets