XA specifies how a transaction manager will roll up the transactions against the different data-stores into an "atomic" transaction and execute this with the two-phase commit (2PC) protocol for the transaction.
Transmission Control Protocol | File Transfer Protocol | Session Initiation Protocol | User Datagram Protocol | BitTorrent (protocol) | Kyoto Protocol | Internet Protocol | Post Office Protocol | Program and System Information Protocol | Simple Network Management Protocol | Internet Message Access Protocol | Network File System (protocol) | Hypertext Transfer Protocol | Lightweight Directory Access Protocol | Secure Real-time Transport Protocol | Real-time Transport Protocol | Simple Mail Transfer Protocol | phase | Montreal Protocol | Communications protocol | Wireless Application Protocol | SSH File Transfer Protocol | Remote Desktop Protocol | Point-to-Point Protocol | phase (waves) | Phase-change material | Phase | Internet protocol | Dynamic Host Configuration Protocol | 2010–11 UEFA Europa League qualifying phase and play-off round |
3PC was originally described by Dale Skeen and Michael Stonebraker in their paper, “A Formal Model of Crash Recovery in a Distributed System”.