Wikipedia defines system integration as 'the bringing together of component subsystems into one system and ensuring that the subsystems function together as a system." It is also about "value-adding to the system, capabilities that are possible because of interactions between subsystems." In the application development world, "subsystems" may include a mixture of hardware (web servers, database servers, networks and firewalls) and software (SQL Server, .NET, html, php, classic ASP, etc).
A classic example of an integrated system is a dynamically driven website.
This is a combination of subsystems such as a web server, Internet Information Services (IIS), .NET framework with C# common runtime language, ISAPI Rewrite, and a SQL Server database. In order for these subsystems to work together as a functioning website, it requires the efforts of system engineers, website designers, website programmers and digital marketing professionals. Without one of those subsystems in place or only one of them is not integrated properly, the compilation of subsystems is a jumbled mess of components that do not work in synergy with each other. The synergistic website http://www.smtusa.com effectively combines all of these subsystems into a powerful, dynamic, optimized and beautiful website.
An example of a third party integration is an email system for one of our clients that runs independent of their website.
In fact, a website is not even needed for this integrated system. The software combines several sources of data retrieved from a third party vendor and performs database matches against the data.
For example, specific data contains a list of buyers and the criteria those buyers are looking for in a particular service. The other data contains lists of services and the associated service attributes. When matches occur, emails are sent to the buyer as well as the service provider to inform them of those matching buyers and services. It is a well oiled machine: an integrated system.