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Quality Attributes Scenario Components

When we are talking about the quality attributes of an application we risk to talk all night without approaching the end of the topic. The main scope of this article is to see what are the main components of a scenario that can define a quality attribute.
There are a lot of quality attributes that can be involved. There are 6 attributes that are very common and extremely important in a solution:
  1. Availability
  2. Modifiability
  3. Performance
  4. Security
  5. Testability
We saw the most important quality attributes and it would be very easy for us to find another 10. All this attributes are executed based on a predefined scenario. The components of the scenario can be isolated and used to identify, describe and understand each attribute.
Each quality attribute has a SOURCE OF STIMULUS. There is an entity that generates the stimulus. In a simple scenario we can have a person, but the stimulus can be another system, a handler or even a specific time. This stimulus is the source that triggers the specific action, event or any kind of behavior. For example we can imagine as a stimulus the person who starts the computer.
Beside source of stimulus we have the STIMULUS. This represents the condition that needs to be taking into account when the stimulus arrives into the system. For example the “desire” to start the computer. It is very important to understand that the source of stimulus and stimulus itself are two different thing and don’t need to be combined. Different sources of stimulus can produce the same stimulus but the measurements can be different. For example is not the same thing to have as source of stimulus the person that is near the computer and can push the start button or when we have a person that is 1000 km away and need to fly to the specific location to start the system.
The 3th part of an attribute is the ENVIRONMENT. The action is executed in a specific scenario, were specific resources are available or certain components are active. Because of this the environment is very important for each scenario. For example the hardware configuration of the system where the operation system is installed. It is not the same thing to run a Windows 8 or on a i7 or on a Pentium 4.
Next thing of quality attribute scenario are ARTIFACTS. These can represent only a part of a system or the whole system. This represents the component/system that is measured. There are cases when we want to measure all the system or we need to measure only a part of a system (for example the module that initializes the kernel of operation system). Any action that is executed will generate a response.
 The 5th item is RESPONSE. The response is not all the time visible to the source of stimulus. For example starting operating system of a server that doesn’t has a monitor represent a state change of the running system.
From the moment when the stimulus is generated to the moment when the response is send we need to measure different parameters. These form the last item of our scenario which has been named RESPONSE SCENARIO.  Each response needs to be measurable in one way or another. In our example, the most important thing can be how long the operation system needs to start, but in other cases we can have different parameters (e.g. the monitor).

These are the components that form the scenarios that are used for quality attributes. When we are trying to define the quality attributes of a system we should think about this 6 components.


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