B2B Integration : A Practical Guide to Collaborative E-commerce

78 B2B Integration — A Practical Guide to Collaborative E-commerce
the output may be a user-defined type or a system-defined type. Userdefined
types are used for storing groups of related information by
containing combinations of multiple individual data members. This
grouping and encapsulation of data helps in passing a single input
parameter instead of a large number of parameters and/or returning a
logical object that contains all the data as desired from the output of a
method call.
Named Constants — In several cases, APIs use fixed numeric or string
codes, also known as constants, to represent some kind of constant
information or value. Naming these constants provides a more convenient
way to refer to their values in code.
Callback Functions — Callback functions are an optional feature of an
API. Callback functions are regular functions defined in the programs
implementing APIs with the exception that they are never made available
through an interface. They are used internally by one or more of the
API functions to perform the task.
Classes of APIs
Based on their functionality and uses, APIs can be classified into five
different classes. Although there is considerable similarity in these
classes, they broadly cover all the different approaches in which packaged
applications (i.e., ERP, CRM, SCM), databases, legacy systems or
custom developed applications can expose their methods in the form of
interfaces.
Method APIs — Method APIs provide an interface for a series of
methods or functions exposed by an application, which the external
applications can invoke. Each method is defined by a name, a set of
input parameters (which must be provided by the calling application in
order to use the method), output type and exceptions.
Several leading packaged software vendors provide linkable libraries.
For instance, external applications can access SAP Business Objects
through standardized, platform-independent interfaces — Business
Application Programming Interfaces (BAPIs).