Each message between business elements on a sequence diagram must be supported by a structural relationship. For
instance, a business worker can't request that a business entity perform an operation without having some way to
inform the entity of the request. The nature of the relationship depends on what the element is, so the relationship
could represent a network connection, an interpersonal relationship, a business contract, etc.
See Example: Class Diagram realizing a Business Use Case for an example of a business
use-case realization structure.
Identify the Relationships in a Sequence Diagram
Create one UML class diagram for your business use-case realization. This diagram illustrates the structure required to
support all relationships needed to realize the scenarios in the business use-case realization. Add all the business
elements from all the sequence diagrams into the class diagram. There will likely be many business elements that appear
in multiple sequence diagrams. These only need to be added to the class diagram once.
For each message or request that's made from one business element to another, add a one-way association in the
class diagram from the requesting element to the element that performs the requested operation. If you find two
elements that make requests of each other, use a single bi-directional association. If a relationship from one entity
to another already exists, leave it alone (any number of operations can be requested using a single relationship)
Add Multiplicity and Roles
Examine the relationships and determine their multiplicity. Start with 1-to-1 relationships and ask if one element
needs to access more than one instance of another element. For example, sequence diagrams can show that a service
supports requests from various business elements of the same type. If it can handle those requests in parallel, there
will be a many-to-one relationship between the elements.
Check Diagram for Readability and Consistency
Review the diagram to assure it's readable and properly describes the relationships between business elements. Make any
changes necessary that will improve the accuracy and usability of the information.
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