At this point, the Purchasing
system could determine the spending limits of the purchaser and to what
department the accounting should be tied. In practice, these online interfaces are difficult
to build because they require the systems to agree, and remain in agreement,
about how to communicate. Each system has proprietary application programming
interfaces (APIs) that allow other systems to communicate with them. These specific,
and often conflicting, APIs limit the reuse of the functionality within each
system.
Object technologies offer one solution: systems communicate by invoking methods
on objects instead of by calling specific APIs. For example, if youwant to check the
department of a user, you make a standard object call to the employee object managed
by the HR system.
Oracle8i and later versions support a number of object technologies, including Java
for use as an object-oriented programming language. Oracle??™s object-oriented
support is described in more detail in Chapter 14. More recently, the focus on
developing applications and code for reuse now includes the concept of a Service-
Oriented Architecture (SOA) and web services, described in Chapter 15.
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