Systems Integration is the practice of building turn- key software and hardware solutions without getting involved in the software development process. Systems integration focuses on productizing a software and hardware solution so that it can be delivered to a 3rd party that has a relatively weak understanding of technology. A System Integrator (SI) is someone who delivers systems integration solutions for a client using Commercial Off-The Shelf (COTS) software. They are responsible for executing the project, configuring the software, and installing the solution.
System integration (SI) is an IT or engineering process or phase concerned with joining different subsystems or components as one large system. It ensures that each integrated subsystem functions as required.
SI is also used to add value to a system through new functionalities provided by connecting functions of different systems.
Horizontal Integration: Involves the creation of a unique subsystem that is meant to be the single interface between all other subsystems, ensuring that there is only one interface between any subsystem and any may be replaced with another without affecting the others by using totally different data and interfaces. This is also known as an Enterprise Service Bus (ESB).