SDKs are of two different types Mac OS X and iOS, the Mac OSX SDKs has frame works and headers which would allow responding Mac OS X version number. iOS SDK functions same but it also has additional features like bundled compliers and iPhone simulator. The important factor in building system related to SDKs and OS is base SDK and Mac OS X or iOS Deployment Target. The base SDK refer to MAC OS X or iOS deployment target. It also refers to the base used to structure the application and it should be most current.
The integration refers to the minimum OS desired for application, as there is one point for release back note which is iOS SDK 4.0 and the iPhone simulator can be tested on universal apps in iPad Simulator(iOS 3.2) or iPhone Simulator(iOS 4.1) from universal make.
Xcode is complete developers testing tool to create application for Mac, iPhone and iPad. An Xcode IDE performance analysis tool helps iPhone and iPad simulators with OS framework packages with form of Mac OS x SDKs and iOS SDKS.
Xcode compatibility: Xcode 3.2 involves an Intel based Mac running Mac OS X snow leopard version 10.6.4 or later. XCode is an IDE. iOS SDK (Software DevelopmentKit) is a set of development tools (mostly in the form of libraries) that you use to create applications with. The new Xcode 4 has added new features with several unique UI elements that make things easy to work on many different tasks also into multiple projects with hampering the work area