Examine the relevant Use Case(s) and Supporting Requirements to understand the scope of the design task and the expectations on the Design. Work with the Stakeholder and Analyst to clarify ambiguous or missing information.

If the requirements are not represented in some sort of scenario form (for example a non-functional requirement might not have a scenario associated with it), a scenario will have to be identified that appropriately exercises the requirements under consideration.

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.

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.

Identify the required relationships between the elements based on the walkthrough of the scenario examining how the elements initiate each other's behavior. An element that requests behavior from another element is represented as a relationship between those elements. 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. Use the Architect to explain the details and motivations of the architecture. 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.

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.  Revisit the identification of the elements and the collaborations that realize the scenarios if necessary as this refinement takes into consideration details at a lower level of abstraction. Discuss testability issues, such as design elements that are difficult to test or critical performance areas, with the Tester and Architect.

In particular make decisions in regard to the considerations below:

• Specific details of relationships between the elements such as multiplicity and navigability
• Operation detail such as parameters and return values
• Existence and detail of data attributes necessary
• 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.

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. Add additional operations, attributes, and relationships to support the expectations of an element. Discuss testability issues, such as design elements that are difficult to test or critical performance areas, with the Tester and Architect.

The state of the element managed over the course of its lifetime can be designed to ensure proper behavior in various usages.

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.

Here are some ways to communicate the design:

• Formal models specified in UML .
• Informal diagrams that render static structure and capture dynamic behavior.
• Annotated code that communicates information about the static structure supplemented with textual descriptions of dynamic behavior across code modules .
• Physical data models to describe the database schema.

Here are some examples of individuals who will need to understand the design:

• Developers who will implement a solution based on the design.
• 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.
• Other designers who can examine the design for applicability to other parts of the system.
• Developers or other designers who will be working on other parts of the system that will depend on the elements designed in this task.
• Other reviewers who will review the design for quality and adherence to standards.

If the system has persistent data, the design will need to address the database (or file) schema.  For a relational database schema, identify the following:

• The structure of tables and views
• Relationships between tables
• Triggers which enforce referential integrity
• Constraints on columns
• Default values for columns
• Stored procedures and functions

Evaluate the object design for coupling, cohesion, and other quality design measurements.

Evaluate the database/file design for performance, referential integrity, and normalization.

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. Use the Tester and Architect to provide perspectives on design quality and adherence to the architecture. However, when identifying potential reviewers keep in mind that if someone can add value by reviewing the design, then perhaps they could have added even more value by actively participating in the design effort itself.

If design flaws are identified, improve the design.