I don't understand how this is done.
The answer depends on the specific reader employed. Some companies, particularly those offering active RFID-based real-time location systems (RTLS), have complete systems enabling software and a reader to communicate via either an Ethernet or Wi-Fi connection. Proprietary passive systems may have proprietary interfaces between computer systems and their readers, or they might require a custom application programming interface.
Passive ultrahigh-frequency (UHF) readers based on the Electronic Product Code (EPC) use something called Low-Level Reader Protocol (LLRP), which is a standard interface between a reader and middleware or enterprise applications. LLRP essentially establishes the communications protocol between software and a reader, so that any passive UHF reader utilizing LLRP can communicate with any software that uses that protocol.
—Mark Roberti, Founder and Editor, RFID Journal