Free Sequence Diagram Tool

Visual Paradigm Community - the Best #1 FREE Sequence Diagram Tool in the market

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Visual Paradigm Community Edition was launched since 2004 to provide a free UML software for sole non-commercial purpose, supporting users who was making their first steps in UML modeling, and who need a free and cross-platform UML modelling software for personal use, such as applying UML on student projects.

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What is Sequence Diagram?

Sequence Diagram is a model describing how groups of objects collaborate in some behavior over time which captures the behavior of a single use case. It often shows objects and the messages that are passed between these objects for the particular use case which can be used to model:

  • A model describing how groups of objects collaborate in some behavior over time.
  • The diagram captures the behavior of a single use case.
  • It shows objects and the messages that are passed between these objects for the particular use case.

Sequence Diagrams are interaction diagrams that detail how operations are carried out. Interaction diagrams model important runtime interactions between the parts that make up the system

Sequence Diagram in UML Diagram hierarchy

Sequence Diagram For Modeling General Interaction

  • Model high-level interaction between active objects in a system
  • Model the interaction between object instances within a collaboration that realizes a use case
  • Model the interaction between objects within a collaboration that realizes an operation
  • Either model generic interactions (showing all possible paths through the interaction) or specific instances of a interaction (showing just one path through the interaction
  • Capture the interaction that takes place in a collaboration that either realizes a use case or an operation (instance diagrams or generic diagrams)
  • Capture high-level interactions between user of the system and the system, between the system and other systems, or between subsystems (sometimes known as system sequence diagrams)

Sequence Diagram Example: Hotel System

Sequence Diagram is an interaction diagram that details how operations are carried out -- what messages are sent and when. Sequence diagrams are organized according to time. The time progresses as you go down the page. The objects involved in the operation are listed from left to right according to when they take part in the message sequence.

Below is a sequence diagram for making a hotel reservation. The object initiating the sequence of messages is a Reservation window.

Sequence Diagram Example

Note That: Class and object diagrams are static model views. Interaction diagrams are dynamic. They describe how objects collaborate.

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But even with all these benefits above, Visual Paradigm Community is free for all sorts of non-commercial use, since 2004, and for now & forever!

Modeling Use Case Scenarios with Sequence Diagrams

A scenario is one path or flow through a use case that describes a sequence of events that occurs during one particular execution of a system. Sequence diagrams often be used to assist for elaborating use cases by emphasizing message exchange. The various scenarios of a use case can be depicted by a sequence diagram. The representation is restricted to the message exchange within each business use case. Generally, the level of detail for these sequence diagrams is higher than for sequence diagrams spanning use cases.

Use Case vs Scenarios

A use case is a collection of interactions between external actors and a system. In UML, a use case is "the specification of a sequence of actions, including variants, that a system (or entity) can perform, interacting with actors of the system." Typically each use case includes a primary scenario ( or main course of events) and zero or more secondary scenarios that are alternative courses of events to the primary scenario

Representing Use Case Scenarios

User requirements are captured as use cases that are refined into scenarios. A use case is a collection of interactions between external actors and a system. In UML, a use case is:

"the specification of a sequence of actions, including variants, that a system (or entity) can perform, interacting with actors of the system."

A scenario is one path or flow through a use case that describes a sequence of events that occurs during one particular execution of a system which is often represented by a sequence diagram.

Sequence Diagram for Use Case

Sequence Diagram - Model before Code

Sequence diagrams can be somewhat close to the code level, so why not just code up that algorithm rather than drawing it as a sequence diagram?

  • A good sequence diagram is still a bit above the level of the real code
  • Sequence diagrams are language neutral
  • Non-coders can do sequence diagrams
  • Easier to do sequence diagrams as a team
  • Can be used for testing and/or UX Wireframing

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