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Enterprise Systems 25

Much of the work you do on the Internet uses a three-tier architecture.
Your browser is the presentation layer. Through your browser, you connect
to many systems (websites) that provide a variety of capabilities (e-mail, pur-
chasing goods, information sharing). These websites contain the applications
that execute the request you send through the browser (via HTTP), and they
retrieve and store data in a connected database.
The shift to the three-tier client-server architecture dramatically reduced
the costs of acquiring, implementing, and using an ES while signifi cantly
increasing the scalability of the systems. Scalability refers to the ability of the
hardware and software to support a greater number of users easily over time,
typically at a decreasing cost per user. These two benefi ts transformed ES from
a capability that only a few large companies could afford into a technology that
tens of thousands of companies now utilize.

Service-Oriented Architecture
In the early 2000s, companies began to Web-enable their three-tier applications
so that users could access the systems through a Web browser. During these
years companies also benefi ted from new technologies that could help link,
or integrate, many different client-server systems together in new and valu-
able ways. These new technologies are collectively labeled service-oriented
architecture, or SOA. The fundamental concept behind SOA relates to the
technical capabilities that allow systems to connect with one another through
standardized interfaces called Web services. By using Web services, companies
could now integrate multiple client-server applications and create enterprise
mash-ups, or composite applications. Composite applications and mash-ups
rely on Web services to send and receive data between and among ES in a
standardized way, which eliminates a great deal of cost and complexity from
integration projects. In addition, they execute newer and more specifi c pro-
cesses than are typically found in the standard ES.
Companies such as SAP have invested billions of dollars to service-enable
their applications so that these systems can be exposed—that is, their function-
ality can be made visible to users—and can be connected to a great number of
composite applications. By using SOA to integrate and expose the business
processes and data inside an ES, companies can now create new composite
applications quickly and inexpensively. In essence, SOA enables companies
to build composite applications on top of their existing three-tier client-server
applications without changing the underlying applications. This capability
gives companies an entirely new level of fl exibility at an extremely low cost.

ENTERPRISE RESOURCE PLANNING (ERP) SYSTEMS
Enterprise resource planning (ERP) systems are the world’s largest and
most complex ES. ERP systems focus primarily on intra-company processes—
that is, the operations that are performed within an organization—and they
integrate functional and cross-functional business processes. Typical ERP
systems support Operations (Production), Human Resources, Finance &
Accounting, Sales & Distribution, and Procurement. As we discussed in
Chapter 1, SAP was the fi rst company to create a fully integrated and global
ERP system, SAP R/3, which could manage end-to-end processes for com-
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panies that operated in many different countries, with multiple languages and

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