System integration is the bringing together of the component subsystems into one system and ensuring that the subsystems function together as a system. In information technology, system integration is the process of linking together different computing systems and software applications physically or functionally.
Vertical integration is a process of integrating subsystems according to their functionality by creating functional entities. The benefits of this method is that the system integration is performed quickly and involves only the necessary vendors.
Start Integration is a process of integration of the systems where each system is interconnected to each of the remaining subsystems. The cost of this method of integration can vary due to the interfaces which subsystems are exporting.
Horizontal Integration or Enterprise service bus is a method in which a specialized subsystems (BUS) is added to the system and is dedicated to communicate with other subsystems. This system allows cutting the costs of integration and provides extreme flexibility.