MDSD Step 1: Define the system context
Defining the system context is the first step in the MDSD process.2 First of all, we define the context of any system to be an enterprise. If we consider the system to be level 1 in system decomposition levels, then the enterprise is level 0. As noted
before, this also applies more
is level
By examining the enterprise, its goals, and its components, we will understand the system in its context. The goals of an enterprise will be realized by its collaborations with external entities and supported by the collaboration of internal components. These internal components (or entities, to use a slightly less overloaded term) will collaborate through a set of enterprise operations to support the enterprise’s collaboration with its enclosing context. Any enterprise operation that our system under consideration participates in will in fact be a candidate, if not an actual, system use case. To determine what the enterprise operations are, we must analyze the enterprise’s use cases and actors. In other words, we must understand the collaboration of the enterprise with its actors to discover its operations. These operations lead to system use cases. Additionally, the other internal entities of the enterprise are usually our system’s actors.
Actors and boundaries
In the following sections we discuss discovering actors and use cases as part of understanding the context of the system under consideration.
MDSD Step 2: Finding actors
After choosing an entity in your MDSD model, the next step is to find actors for this entity.3 Actors represent the roles played by entities (either a person or another system) in relation to the entity under consideration. By definition, they are outside the entity and interact with it.
For example, if we are building a guidance system within a commercial aircraft, and the aircraft is our entity, then it is likely the passengers would be its actors, while the captain and crew can be represented as part of the aircraft, and thus are not actors. To be a little more exact, we are not representing the passenger as an actor, we are actually representing the passenger role. Actors represent the roles played by people and outside systems in relation to our entity. Other actors for the commercial aircraft might include the control tower, regional air traffic control center, and the ground crew.
2See also Task: Define the system context in the Rational Unified Process (RUP) v7
3Ibid, Task: Find Actors and Use Cases
