Package,Application Component,Software Component
Package, application component and software component are all used to organize SAP repository objects. In order to identify different purpose of repository objects, we assign the repository object to the package.
The package will then assign to a surrounding package and it will also assign to a application component, software component. Below screen shot shows the relationship below them.
Application component classifes the package from the functionality point of view. Like BC (basis component), AP (application component) and SD (sales and distribution). While software component is involved because of the distribution of the SAP software. For example, there are SAP_BASIS,SAP_ABA,SAP_APPL and etc. There is a special software component named HOME which content is delivered by the customer.
Change request is used to organize the change of repository objects and transport them to other systems.