
142 CHAPTER SEVEN
Separation of interface from implementation
The ALE specification provides an interface between clients and RFID middleware,
while leaving the implementation details to the vendors. This approach allows vendors
choices in terms of technology platforms, deployment options, add-on features, and so
on. For example, the software providing an ALE service could be deployed as a standal-
one module at the edge or inside of an application container, or it could reside on an
RFID reader. Each deployment option has its own benefits and drawbacks. The imple-
mentation details are left to you.
The Application Level Events specification provides a WS-*-compliant web services bind-
ings interface for accessing application-level events services. Implementations have the
flexibility to expose the ALE interface using either a wire protocol (such as SOAP/HTTP)
or a language API.
Before diving into the ALE service interface, let’s first familiarize ourselves with some
important concepts and terms.
Key Concepts and Terminology
To understand how the ALE specification works, we need to describe some key concepts
and terms. We will begin by describing event originators. We will then look at read cycles
and event cycles. Once we understand the concepts behind event originators and event
cycles, we will look at the primary interaction models supported between applications and
RFID middleware that implements ...