B2B Integration : A Practical Guide to Collaborative E-commerce

Integration Patterns 11
system programs. Therefore, if a program has to read some data from a
file or write some data to a file, all it does is invoke a method on the 1/
O API provided by the operating system and let the operating system
perform the task of seeking, reading and writing from the hard disk bit
by bit.
Most of the packaged applications such as ERP, CRM and SCM
provide APIs to interact with the underlying application and business
objects. These APIs are independent of the platform and programming
language. This feature gives companies flexibility in terms of integrating
their already developed internal applications, irrespective of their
language and platform, with the packaged software.
Usually all the APIs are synchronous in nature, i.e., the function call
does not return until the specified action is complete. However, if the
application invoking a function call through an API does not want the
client process to wait indefinitely, it can spawn a new thread process to
handle other tasks.
Components of APIs
There are several components of an application programming interface,
as follows:
Interfaces — Interfaces contain the signatures or definitions of the API
functions. They are distributed and used by all the client programs to
invoke API functions. A typical function signature contained in an API
will have the following information:
• Name of the function or method;
• Input parameters;
• Return type (output); and
• Any exceptions thrown by the function.
Methods or Functions — The methods or functions contain the actual
code that performs the tasks defined by the API and are defined and
contained in the underlying programs. If there is any change in the
implementation of a function, its function code has to change.
Input and Output Parameters — Each API function can take multiple
input parameters and may return an output. The input parameters and