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Chapter 1 Internet Era: E-Commerce 17
online commerce. Lets start with the client/server model and make our way up
to the more advanced cloud computing paradigm because that is how scalable
e-commerce sites have started and ended up. This section is more technical in
nature so fasten your technical seatbelts as the fun is about to start.
Client/Server
In the first chapter, we covered the basics of computing and noted its primary
model: standalone computing in a single system. The standalone computing
paradigm is usually monolithic. That is, a combination of all the steps neces-
sary to complete a task is put in a program and once you run the program it
handles the tasks in one piece. The next step in the computing paradigm is to
identify generic tasks and devise components that are responsible for handling
only those specific tasks. One model of achieving this goal is to divide the tasks
into client and server tasks respectively. A client/server computing paradigm
usually has the following constructs:
Service:
Client/server is primarily a relationship between processes run-
ning on separate machines. The server process is a provider of services.
The client is a consumer of services. In essence, client/server provides a
clean separation of function based on the idea of service.
Shared resources:
A server can service many clients at the same time and
regulate their access to shared resources.
Asymmetrical protocols:
There is a many-to-one relationship between
clients and server. Clients always initiate the dialog by requesting a service.
Servers are passively waiting on requests from the clients.
Transparency of location:
The server is a process that can reside on the
same machine as the client or on a different machine across a network.
Client/server software usually masks the location of the server from the
clients by redirecting the service calls when needed. A program can be a
client, a server, or both.
Mix and match:
The ideal client/server software is independent of hard-
ware or operating system software platforms. You should be able to mix
and match client and server platforms.
Message-based exchanges:
Clients and servers are loosely coupled systems
that interact through a message-passing mechanism. The message is the
delivery mechanism for the service requests and replies.
Encapsulation of services:
The server is a “specialist.” A message tells a
server what service is requested; it is then up to the server to determine
how to get the job done. Servers can be upgraded without affecting the
clients as long as the message interface is not changed.
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