Understand requirement details
Examine the relevant requirements to understand the scope of the design task and the expectations on the design.
If the requirements are determined to be incomplete or incorrect, work with the analyst to get the
requirements improved and possibly submit a change request against the requirements.
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Identify design elements
Identify the elements that collaborate together to provide the required behavior. This can start with the key
abstractions identified in the architecture, domain analysis, and classical analysis of the requirements (noun
filtering) to derive the elements that would be required to fulfill them.
Identify elements in all perspectives being considered when performing this task. This could include identifying
user interface elements, control elements, data elements, and elements relating to interfacing to other
systems or devices.
Existing elements of the design should be examined to see if they should participate in the collaboration. It is
a mistake to create all new elements in each execution of this task.
This list of candidates must be expanded to include special-purpose participants that handle particular roles in
providing the required behavior such as transaction processing or adherence to some security specification. The
Entity-Control-Boundary Pattern provides a good start for identifying elements.
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Determine how elements collaborate to realize the scenario
Walk through the scenario distributing responsibilities to the participating elements. These
responsibilities can be simple statements of behavior assigned to elements; they need not be detailed operation
specifications with parameters, etc. This step is about ensuring that a quality model is being created that is
robust enough to support the requirements.
Identify the required relationships between the elements based on the walkthrough of the scenario examining
how the elements initiate each other's behavior. As with the responsibilities, these relationships can just
be defined at this step.
Look to the architecture and previous design work to create a consistent collaboration. Look to reuse existing
behavior and relations or to apply similar structure to simplify the design of the overall system.
Additional elements might be identified as behavior is found that cannot appropriately be assigned to any of the
existing elements.
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Refine design decisions
Refine the design to an appropriate level of detail to drive implementation and to ensure that it fits into the
architecture. In this step the design can take into consideration the actual implementation language and other
technical decisions. As refinement takes into consideration details at a lower level of abstraction, this might
necessitate revisiting the identification of the elements and the collaborations that realize the scenario.
In particular make decisions in regard to
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specific details of relationships between the elements
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operation detail
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existence and detail of data attributes necessary
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usage of inheritance and interfaces to improve the design
Incorporate design mechanisms from the architecture. Apply consistent structure of the elements and organization
of the behavior as in other areas of the design and use patterns identified in the architecture.
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Design internals (for large or complex elements)
Design large or complex elements or some complex internal behavior in more detail.
This might just involve devising an algorithm that could be performed to produce the desired behavior. This could
involve another whole pass through this task where the scenario under consideration is one behavior element of an
element that requires significant design consideration. Add additional operations, attributes, and
relationships to support the expectations of an element.
The state of the element managed over the course of its lifetime can be designed to ensure proper behavior in
various usages.
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Communicate the design
Communicate the design to those who need to understand it. Though this is described here toward the end of
the task, communication should be going on throughout the steps; working collaboratively is always better than
reviewing the work after it is complete.
Some ways to communicate the design are:
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formal models specified in UML
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informal diagrams that static structure and capture dynamic behavior
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annotated code that communicates information about the static structure supplemented with textual descriptions of
dynamic behavior across code modules
Examples of individuals that will need to understand the design are:
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developers who will implement a solution based on the design
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an architect who can review the design to ensure that it conforms to the architecture or who might examine the
design for opportunities to improve the architecture
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other designers who can examine the design for applicability to other parts of the system
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developers or other designers who will be working on other parts of the system that will depend on the
elements designed in this task
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other reviewers who will review the design for quality and adherence to standards
When considering reviewers, keep in mind that if someone can add value by reviewing the design, then they could have
added even more value by actively participating in the design effort itself.
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Evaluate the design
Evaluate the design for coupling, cohesion, and other quality design measurements.
Consider the design from various angles to ensure that it is a high-quality, communicable design. Work with other
technical team members; an independent party can provide a fresh perspective.
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