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Constructing Sequence Diagrams {#constructing-sequence-diagrams .title}
The following checklist shows the necessary steps for the construction of sequence diagrams. Subsequently, we will further explain the individual steps.
Checklist 3.5 Constructing Sequence Diagrams in the External View
- Designate actors and business system---Who is taking part?
- Designate initiators---Who starts interactions?
- Describe the message exchange between actors and business system---Which messages are being exchanged?
- Identify the course of interactions---What is the order?
- Insert additional information---What else is important?
- Verify the view---Is everything correct?
Designate Actors and Business System---Who is Taking Part?
Sequence diagrams illustrate the interactions between actors and the business system. Fundamentally we have a pool of interaction partners from the use case diagrams. Depending on the flow that is being depicted in the sequence diagram, the appropriate actors and business systems can be selected from this pool.
In our case study (see Figure 3.24), we find the interaction partners passenger and passenger services for the above sequence diagram (Figure 3.23):
Designate Initiators---Who Starts Interactions?
For every sequence of interactions the actor who starts the interaction has to be identified. This actor is called the initiator. Since in the external view of the business model each business use case is initiated by an actor, we can here also select the actor from the pool of actors in the use case diagrams.
In our sequence diagram passenger check-in, the passenger starts the interaction by utilizing the service check-in from passenger services.
Describe the Message Exchange between Actors and the Business System---Which Messages are being Exchanged?
After the initiator has been defined, the subsequent progression of interactions has to be identified. For each communication step it has to be determined what information is exchanged. In this way the message will be defined. Messages are requests to do something directed toward a particular partner. The business objects that are exchanged with these messages also have to be defined.
Identify the Course of Interactions---What is the Order?
All messages are exchanged in a chronological order that has to be identified. Messages are inserted along the y-axis in increasing chronological order, from top to bottom (see Figure 3.25):
Insert Additional Information---What Else is Important?
Important activities of involved actors and business systems and important conditions can be inserted into the diagram as comments. Comments are inserted at the level of the appropriate message. Restrict this to important comments that have significance so that the diagram is not overcrowded with text (see Figure 3.26):
Verify the View---Is Everything Correct?
Completed sequence diagrams can be verified with the following checklist:
Checklist 3.6 Verifying Sequence Diagrams in the External View
- Are all required sequence diagrams completed and available? There should be a sequence diagram for each business use case.
- Are the sequence diagrams correct? Each sequence diagram contains only one object that represents the business system, and at most as many other objects as there are actors assigned to the business use case.
- Is each actor that is listed in the use case diagram mentioned in at least one sequence diagram?
- Is each actor who initiates a business use case mentioned as a starting point in one of the sequence diagrams?
- Have all the important comments been inserted into the diagram? Are there maybe too many comments inserted into the diagram thereby reducing its clarity?
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- Change Bidirectional Association to Unidirectional
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- Rename Method
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- Replace Error Code with Exception
- Replace Exception with Test
- Dealing with Generalisation
- UML
- Introduction
- Basic Principles and Background
- Modeling Business Systems
- Business Processes and Business Systems
- One Model---Two Views
- External View
- The Elements of a View
- Use Case Diagrams
- Constructing Use Case Diagrams
- Activity Diagrams
- Constructing Activity Diagrams
- Sequence Diagrams
- Constructing Sequence Diagrams
- High-Level Sequence Diagrams
- Sequence Diagrams for Scenarios of Business Use Cases
- Internal View
- Package Diagram
- Constructing Package Diagrams
- Class Diagram
- Constructing Class Diagrams
- Activity Diagram
- Modeling IT Systems
- External View
- The User View or “I don’t care how it works, as long as it works.”
- The Elements of a View
- Use Case Diagram
- Query Events and Mutation Events
- Use Case Sequence Diagram
- Constructing the External View
- Structural View
- Objects and Classes
- Generalization, Specialization, and Inheritance
- Static and Dynamic Business Rules
- Elements of the View
- Class Diagram
- Constructing Class Diagrams
- The Behavioral View
- The Life of an Object
- The Elements of the View
- Statechart Diagram
- Constructing Statechart Diagrams
- Interaction View
- Seeing What Happens Inside the IT System
- Elements of the View
- Communication Diagram
- Sequence Diagram
- Constructing Communication Diagrams
- Constructing Sequence Diagrams
- Modeling for System
Integration
- Terminology of System Integration
- Messages in UML
- One Model---Two Views
- Process View
- The Business System Model as Foundation
- Elements of the View
- Activity Diagrams
- Sequence Diagram
- Constructing Diagrams in the Process View
- The Static View
- Elements of the View
- Class Diagram
- Constructing Class Diagrams
- Transforming Data from the IT System to the Message “passenger list”
- Transformation of UML Messages into Various Standard Formats
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Constructing Sequence Diagrams {#constructing-sequence-diagrams-1 .title}
The following checklist shows the necessary steps for the construction of sequence diagrams. Subsequently, we will further explain the individual steps.
Checklist 3.5 Constructing Sequence Diagrams in the External View
- Designate actors and business system---Who is taking part?
- Designate initiators---Who starts interactions?
- Describe the message exchange between actors and business system---Which messages are being exchanged?
- Identify the course of interactions---What is the order?
- Insert additional information---What else is important?
- Verify the view---Is everything correct?
Designate Actors and Business System---Who is Taking Part?
Sequence diagrams illustrate the interactions between actors and the business system. Fundamentally we have a pool of interaction partners from the use case diagrams. Depending on the flow that is being depicted in the sequence diagram, the appropriate actors and business systems can be selected from this pool.
In our case study (see Figure 3.24), we find the interaction partners passenger and passenger services for the above sequence diagram (Figure 3.23):
Designate Initiators---Who Starts Interactions?
For every sequence of interactions the actor who starts the interaction has to be identified. This actor is called the initiator. Since in the external view of the business model each business use case is initiated by an actor, we can here also select the actor from the pool of actors in the use case diagrams.
In our sequence diagram passenger check-in, the passenger starts the interaction by utilizing the service check-in from passenger services.
Describe the Message Exchange between Actors and the Business System---Which Messages are being Exchanged?
After the initiator has been defined, the subsequent progression of interactions has to be identified. For each communication step it has to be determined what information is exchanged. In this way the message will be defined. Messages are requests to do something directed toward a particular partner. The business objects that are exchanged with these messages also have to be defined.
Identify the Course of Interactions---What is the Order?
All messages are exchanged in a chronological order that has to be identified. Messages are inserted along the y-axis in increasing chronological order, from top to bottom (see Figure 3.25):
Insert Additional Information---What Else is Important?
Important activities of involved actors and business systems and important conditions can be inserted into the diagram as comments. Comments are inserted at the level of the appropriate message. Restrict this to important comments that have significance so that the diagram is not overcrowded with text (see Figure 3.26):
Verify the View---Is Everything Correct?
Completed sequence diagrams can be verified with the following checklist:
Checklist 3.6 Verifying Sequence Diagrams in the External View
- Are all required sequence diagrams completed and available? There should be a sequence diagram for each business use case.
- Are the sequence diagrams correct? Each sequence diagram contains only one object that represents the business system, and at most as many other objects as there are actors assigned to the business use case.
- Is each actor that is listed in the use case diagram mentioned in at least one sequence diagram?
- Is each actor who initiates a business use case mentioned as a starting point in one of the sequence diagrams?
- Have all the important comments been inserted into the diagram? Are there maybe too many comments inserted into the diagram thereby reducing its clarity?
Read next
High-Level Sequence Diagrams []{.fa .fa-arrow-right}{.btn .btn-primary rel=“next”}
Return
[]{.fa .fa-arrow-left} Sequence Diagrams{.btn .btn-default rel=“prev”}
Computer Science Distilled{.btn .btn-landing-ref .btn-hg .btn-block .btn-secondary style=“font-size: 16px; position: relative”}
Do you remember anything at all from your computer science class? Quicksort, Graph traversal, Big’O and other stuff? Revise your memories with our new book on Computer Science.
Psst! Did I mention that we’re offering sexy discounts right now?
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srcset=“/images/content-public/logos/logo-2x.png?id=fee3b4b0a14ba60dc0fe368695d78be9 2x”}{.menu-brand}
- Premium Stuff
- Design Patterns
- AntiPatterns
- Refactoring
- Code Smells
- Refactoring techniques
- Composing Methods
- Moving Features between Objects
- Organizing Data
- Self Encapsulate Field
- Replace Data Value with Object
- Change Value to Reference
- Change Reference to Value
- Replace Array with Object
- Duplicate Observed Data
- Change Unidirectional Association to Bidirectional
- Change Bidirectional Association to Unidirectional
- Replace Magic Number with Symbolic Constant
- Encapsulate Field
- Encapsulate Collection
- Replace Type Code with Class
- Replace Type Code with Subclasses
- Strategy
- Replace Subclass with Fields
- Simplifying Conditional Expressions
- Simplifying Method
Calls
- Rename Method
- Add Parameter
- Remove Parameter
- Separate Query from Modifier
- Parameterize Method
- Replace Parameter with Explicit Methods
- Preserve Whole Object
- Replace Parameter with Method Call
- Introduce Parameter Object
- Remove Setting Method
- Hide Method
- Replace Constructor with Factory Method
- Replace Error Code with Exception
- Replace Exception with Test
- Dealing with Generalisation
- UML
- Introduction
- Basic Principles and Background
- Modeling Business Systems
- Business Processes and Business Systems
- One Model---Two Views
- External View
- The Elements of a View
- Use Case Diagrams
- Constructing Use Case Diagrams
- Activity Diagrams
- Constructing Activity Diagrams
- Sequence Diagrams
- Constructing Sequence Diagrams
- High-Level Sequence Diagrams
- Sequence Diagrams for Scenarios of Business Use Cases
- Internal View
- Package Diagram
- Constructing Package Diagrams
- Class Diagram
- Constructing Class Diagrams
- Activity Diagram
- Modeling IT Systems
- External View
- The User View or “I don’t care how it works, as long as it works.”
- The Elements of a View
- Use Case Diagram
- Query Events and Mutation Events
- Use Case Sequence Diagram
- Constructing the External View
- Structural View
- Objects and Classes
- Generalization, Specialization, and Inheritance
- Static and Dynamic Business Rules
- Elements of the View
- Class Diagram
- Constructing Class Diagrams
- The Behavioral View
- The Life of an Object
- The Elements of the View
- Statechart Diagram
- Constructing Statechart Diagrams
- Interaction View
- Seeing What Happens Inside the IT System
- Elements of the View
- Communication Diagram
- Sequence Diagram
- Constructing Communication Diagrams
- Constructing Sequence Diagrams
- Modeling for System
Integration
- Terminology of System Integration
- Messages in UML
- One Model---Two Views
- Process View
- The Business System Model as Foundation
- Elements of the View
- Activity Diagrams
- Sequence Diagram
- Constructing Diagrams in the Process View
- The Static View
- Elements of the View
- Class Diagram
- Constructing Class Diagrams
- Transforming Data from the IT System to the Message “passenger list”
- Transformation of UML Messages into Various Standard Formats
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