Context diagrams are a great tool for keeping the marketect and the tarchitect in step. A context diagram shows your system in context with other systems or objects with which it interacts . It typically shows your system as a "single box" and other systems/objects as boxes or stylized icons, with interactions between systems shown using any number of notations. Avoid formal notations in context diagrams and instead focus on simple descriptions that capture the important aspects of the relationships between the items contained within the context diagram. Context diagrams are not a formal picture of the architecture but a "higher level" shot that shows the system in the context of its normal use.
Context diagrams are useful for a number of reasons.
The marketect must take primary responsibility for the context diagram, although, of course, other members of the team can and should provide input to it. For example, the tarchitect can identify key standards, salespeople may suggest new entries based on how customers use the product, and so forth.