Often the system boundary is only precisely defined towards the end of the requirements process. Before that, the desired functions and qualities of the planned system are only incompletely known or not known at all. Therefore there will be a grey zone in which the possible system boundary lies. Besides a shifting of the system boundary within the grey zone, the grey zone itself can also shift during the RE process, e.g. when, through a shifting of the system boundary, further aspects of the environment become important.
Also the context boundary can change over time, e.g. when it turns out, contrary to expectations, that a legal requirement, previously classified as relevant, has absolutely no impact on the planned system, then the system context is reduced in this area.
The context boundary also has a grey zone. It comprises the identified aspects of the environment for which, at a particular time, it is unclear whether these aspects have a relation to the planned system or not.
Use case diagrams or data flow diagrams are often used for the documentation of the system contexts (especially the system and context boundaries). In context modeling, based on data flow diagrams, the sources and sinks in the system environment are modeled, showing respectively the source or destination of data flows between the system in consideration and the environment. The actors (i.e. for example people or other systems) in the system environment and their use relations with the system to be developed are modeled in use case diagrams.