dot.NET.Framework.Essentials.1002003,.3Ed [Electronic resources] نسخه متنی

6.1 Web Services in Practice

You may have heard the phrase "software as a
service" and wondered about its meaning. The term
service, in day-to-day
usage, refers to what you get from a service provider. For example,
you bring your dirty clothing to a cleaner to use its cleaning
service. Software, on the other hand, is
commonly thought of as an application, either an off-the-shelf
product, or a custom application developed by a software firm. You
typically buy the software (or in our case, build the software). It
usually resides on some sort of media such as floppy diskette or CD
and is sold in a shrink-wrapped package through retail outlets, or,
in the case of a web application, the software application is not
distributed, but is accessed through a browser.

How can software be viewed as a service? The example we are about to
describe might seem far-fetched; however, it is possible with current
technology. Imagine the following. As you grow more comfortable with
the Internet, you might choose to replace your computer at home with
something like an Internet Device, a large-screen PDA designed for
use with the Internet. Let's call the device an
iDev. Let's suppose that with this device, you can
be on the Internet immediately through your cell phone, WiFi, or some
other means. When you want to do word processing, your iDev is
configured to print to a Microsoft Word service somewhere in Redmond,
so you can type away without the need to install word-processing
software. When you are done, the document can be saved at an iStore
server where you can later retrieve it. Notice that for you to do
this, the iStore server must host a software service that allows you
to store documents. Microsoft might charge you a service fee based on
the amount of time your word processor is running and the features
you use (such as the grammar and spell checkers). The iStore service
charges might vary based on the size of your document and how long it
is stored. Of course, none of these charges would come in the mail,
but rather through an escrow service where the money would be
withdrawn from your bank account or credit card.

As long as your document is in a standard format, such as XML,
you're free to switch word processors at any time.
Of course, the document that you store at the iStore server is
already in a standard data format. Since iStore utilizes the
iMaxSecure software service from a company called iNNSA (Internet Not
National Security Agency), the security of your files is assured. And
because you use the document storage service at iStore, you also
benefit from having your document authenticated and decrypted upon
viewing, as well as encrypted at storing time.

While this particular vision of software as a service has yet to be
realized, a variety of for-fee and free services have begun to
appear. In early 2001, Microsoft announced plans for an integrated
collection of consumer-oriented services (known first by their
codename,
"Hailstorm," and later as ".NET
My Services") but was forced to abandon the
initiative for a variety of reasons, some technical and others legal,
political, or market-related. Today, Microsoft offers a variety of
user-centric services for identification and authentication, email,
instant messaging, automated alerts, calendar, address book, and
personal information storage. These are available through its MSN
online services, and through Passport (http://www.passport.net), Alerts (http://alerts.microsoft.com), MSN Wallet
(http://wallet.msn.com), and
Hotmail.

Of greater interest to developers, however, is the availability of
these services for use as building blocks in third-party web
applications. Hosted by Microsoft and known as Microsoft .NET
Services, Passport, Alerts, and MSN Wallet can each be licensed and
incorporated into any application that adheres to XML web services
standards, regardless of platform. A more recently announced web
service is Microsoft MapPoint .NET, which is a set of services that
allows you to incorporate maps, driving directions, distance
calculations, proximity searches, and other location intelligence
into your applications.

In addition to Microsoft, other companies are beginning to offer
information and functionality as services over the Web. A recent
poster child is Saleforce.com, which offers customer relations
management (CRM) software over the Web, either as a standalone
product or as a set of services that can be incorporated into
third-party applications. The Liberty Alliance is at work defining an
authentication service that can be offered as an alternative to
Microsoft Passport. And both Google and Amazon now make portions of
their business information available through public web service
interfaces.

The potential for consumer-oriented and business-to-business web
services like Microsoft .NET Services is great, although there are
serious and well-founded concerns about security and privacy. In the
mean time, web services can be great in interoperability areas where
there are needs to expose legacy functionalities or to enable
interaction between multiple heterogeneous systems. In one form or
another, though, web services are here to stay, so
let's dive in and see what's
underneath.