In simpler words, a sequence diagram shows how different parts of a system work in a ‘sequence’ to get something done. They illustrate how the different parts of a system interact with each other to carry out a function, and the order in which the interactions occur when a particular use case is executed. Sequence diagrams, commonly used by developers, model the interactions between objects in a single use case. Sequence Diagram Templates and Examples.In this sequence diagram tutorial you will learn about Among the three, sequence diagrams are preferred by both developers and readers alike for their simplicity. These diagrams are used to illustrate interactions between parts within a system. There are 3 types of Interaction diagrams Sequence diagrams, communication diagrams, and timing diagrams. The User View or "I don't care how it works, as long as it works.This sequence diagram tutorial is to help you understand sequence diagrams better to explain everything you need to know, from how to draw a sequence diagram to the common mistakes you should avoid when drawing one. Sequence Diagrams for Scenarios of Business Use Cases Replace Nested Conditional with Guard Clauses Replace Magic Number with Symbolic ConstantĬonsolidate Duplicate Conditional Fragments Unlike activity diagrams, sequence diagrams enable us to see that the business object passenger list is sent as the argument of a message.Īlternative Classes with Different InterfacesĬhange Unidirectional Association to BidirectionalĬhange Bidirectional Association to Unidirectional The individual actions can also be inserted into the sequence diagram as comments however, this carries the risk of decreasing the readability of the sequence diagram. This information is contained in the activity diagram (see Figure 5.11). In the sequence diagram, we cannot see what actions are actually performed so that messages can be exchanged. Once the luggage has been unloaded, baggage transportation sends an appropriate confirmation to passenger services, by sending a list of passengers whose luggage has been unloaded (7).įinally, passenger services confirm (8) that the luggage has been unloaded. On the basis of the passenger list (5), which is received (6) by baggage transportation (3), the affected pieces of luggage are unloaded. Passenger services accepts (4) the request, generates the passenger list, and sends the passenger list back to baggage transportation (6). Reading Sequence Diagrams Figure 5.10 Sequence diagramįigure 5.10 shows that as soon as the prerequisite (2) is fulfilled, baggage transportation requests a passenger list from passenger services (1). However, the sequence diagram adds the chronological aspect. In the system integration model, the message flow of the sequence diagram corresponds to the object flow of the activity diagram: The message flow goes from the sender of the message to the receiver. Information is transferred as arguments:Īrguments can be business objects (see Messages in UML). In sequence diagrams, messages are understood as operations of events. In the system integration model, these objects represent the interacting IT systems: Message Objects exchange messages with each other. In sequence diagrams as shown in Figure 5.9 we work with the following elements: Object The system integration model illustrates the message exchange between IT systems: Figure 5.8 Sequence diagram “No Boarding” Figure 5.9 Elements of the sequence diagram The focus of sequence diagrams lies in the illustration of the chronological sequence of message exchange between objects as shown in Figure 5.8.
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