The short answer is that it occurs via a network connection, either wired or wireless. The longer response depends on the type of reader being used. Remember, there are many different types of radio frequency identification technologies and RFID interrogators, including passive low-frequency (LF), high-frequency (HF) and ultrahigh-frequency (UHF), battery-assisted HF and UHF, active 433 MHz, 900 MHz, 2.45 GHz, ZigBee, ultra-wideband (UWB) and others.
GS1 created a standard application programming interface (API) for readers based on the EPC Gen 2 standard, known as the low-level reader protocol (LLRP). If you are employing any EPC reader, it should interface with your middleware or back-end system via the LLRP.
Other RFID readers have proprietary formats for passing data to middleware or software applications. Some push the data in XML format. Middleware companies have developed some APIs to link their middleware to readers and to SAP, Oracle and other enterprise systems.
—Mark Roberti, Founder and Editor, RFID Journal