Types Of Messages In Sequence Diagram

The drawback of a Sequence Diagram. In the case of too many lifelines, the sequence diagram can get more complex. The incorrect result may be produced, if the order of the flow of messages changes. Since each sequence needs distinct notations for its representation, it may make the diagram more complex. The type of sequence is decided by the.

  1. Sequence Diagram Tool
  2. Describe The Different Types Of Messages In Sequence Diagrams
  3. Types Of Messages In Sequence Diagram Design
  4. What Is Message In Sequence Diagram

Last time we ended with my dilemma either to try and meet a killer deadline or to get sacked. Fibbs, the company’s salesman, managed to sell a software upgrade to an important client. Good job, except that we hadn’t even planned to do such an upgrade. What’s even better, a month’s work was promised to be done, dusted and delivered in just over a week. How about that for a nail-biting cliffhanger? Or is it just me? Probably just me.

Sequence Diagram Tool

An unsettlingly direct message in my case. I can see Fossey, my manager, approaching and I can guess the purpose of his visit.

See also UML Sequence Diagram - For more information about UML Sequence Diagram. You can show or hide sequence numbers of messages. To show or hide sequence numbers of message. There are 3 types of Interaction diagrams; Sequence diagrams, communication diagrams, and timing diagrams. These diagrams are used to illustrate interactions between parts within a system. Among the three, sequence diagrams are preferred by both developers and readers alike for their simplicity. A (basic) message sequence chart or MSC is a diagram that shows communications between system components (also called instances). Each vertical line in an MSC represents a system components, and horizontal arrows represent messages from one component to another. The actor is outside the scope of the sequence diagram and is therefore a found message. A lost message can occur when a message is sent to an element outside the scope of the UML diagram. An asynchronous message is the only message type for which you can individually move the sending and receiving points.

Sure enough, fixing his eyes on the coffee cup circle on my desk, he asks: “Where are we on the Export to Excel feature, can you give me an estimate of how long it might take us to get that done?” What he means is how long it would take me to get it done and what he is actually telling me is: “You heard Fibbs promise that it would be shipped next Friday. Now tell me it’s going to happen, so I can report it to my boss.”

Messages in UML sequence diagrams are the means of communication between participants in the diagram. They are shown as arrows coming out of a participant’s lifeline and going into another participant’s lifeline. Usually to cause disturbance.

A message typically leads to… “stirrings“, shall we say? A stirring could cause a participant to:

  • come up with some sort of a result, often through calculation
  • engage in some other sort of behaviour
  • create another participant
  • even cease to be

“Coming up with some sort of a result” somehow seems appropriate at the moment. I assume a serious expression and proceed to click through the project’s schedule on FogBugz to make it look like I’m actually working on it…

“I’d say a week, if we don’t do the formula export…”
What I want to say is: “You know that would take a month in the best of circumstances. I’m telling you what you want to hear only because I have no choice. Could we cut down on functionality? Please?”

Fossey moves his eyes away from the coffee stain, looks at the ceiling, then back at the coffee stain… “Fine, I’ll go tell Fibbs.” To be understood as: “You know this won’t be possible. But it would make me look better, if pressure came from the salespeople.”

Direct harassment (a tap on the shoulder, for example) is only one way of passing a message to a participant. Just like among people, communication between UML objects can take various forms and this is reflected in the way the messages are drawn on a sequence diagram. In a computer program a message would often represent a function call, so I’m using “message” and “call” interchangeably in this post.

What we saw above was an example of a

  • Synchronous message – the sender is “blocked” or waiting until the receiver does its work and returns. A synchronous message is the simplest one and most often maps to a direct function call.

That would be Fossey glued to my desk’s coffee stain until he got the estimate he wanted…

  • Asynchronous message is used when the sender can remain running (active) while the receiver is reacting to the call. In programming that could be useful for showing multiple threads of behaviour.

I know what that is! That’s when a tester sends me a bug report, for example… It normally gets me to leave whatever I’m doing and get on with the *** bug, while the tester happily goes on doing whatever a tester does. Filling in *** bug reports.

The same symbol is used when the type of message is unknown or unimportant, so it is also referred to as a generic message.

  • A return from a call points from the receiver of a previous message back to the sender. It means that a task has been completed and can also mean that a result has been returned, though the result is not necessary – think about function calls, which may or may not return something.
  • A found message is one, whose sender is unknown, but which causes some change in the system.
  • A lost message is normally sent to an unknown recipient.
  • Timed callnot part of the UML 2.0 standard, but handy for showing that a call will be abandoned, if it is not completed in a certain time.

Function calls often have arguments passed in them:

This syntax is used when showing a call with arguments on a UML sequence diagram:

Putting it all together

Death and taxes are nowhere near as inevitable as pressure from the salespeople. The next morning I come to work to find voice mail from Fibbs, the salesman, reminding me about the deadline next Friday: “… and yeah, if you could you add a way for the columns to change colors, that would be greeeat.”

Trying not to hyperventilate, I rush to my manager Fossey’s office. Either we should negotiate a new deadline or someone will have to explain to the salespeople that color changing Excel columns are about as useful as an MP3 toothbrush. Fossey doesn’t seem to be around, so I wait. I’m not leaving until something is done, for goodness’ sake!

Ten minutes later, after having adored the portraits of Fossey’s wife and bulldog on his desk, though still not certain which one’s which, I drag myself back to my desk. To find Fossey waiting for me and staring at my picture of Lara. I equalize before he scores: “Fibb’sjustrequestedmorefeatures. Nowaythiscanbedonefornextweek!” He asks me to repeat and, this time more coherently, I explain the gravity of the situation. He looks at the floor. Strokes his chin. Then strokes his chin some more, while still looking at the floor. Then mutters something about overtime and that rates for that aren’t bad and wonders off.

I pick up the phone and order pizza. See you next Friday…

  • UML – Unified Modelling Language
  • UML Sequence Diagram – a diagram, which describes a scenario in the behaviour of groups of collaborating objects
  • actor – something or someone, interacting with a system, but not part of it
  • lifeline – a line, representing the life span of a participant in the scenario
  • message – a line of communication between participants in the scenario (see “Messages in UML 2.0 Sequence Diagrams” for details on the types of messages and their use)
  • Class Diagram – a digram, which shows classes (object types), participating in a system, their properties and the relationships between them
  • Class Properties represent the features of a class, which can be attributes or associations

As much as I would like to take credit for the knowledge in this article, all the UML stuff comes from:

  • – The UML Standard
  • – “UML Distilled Third Edition” by Martin Fowler
  • – “UML 2 for Dummies” by Michael Jesse Chonoles, James A. Schardt
  • UML Tutorial
  • UML 2.0 Overview
  • UML Useful Resources
  • Utilities
  • Selected Reading

From the term Interaction, it is clear that the diagram is used to describe some type of interactions among the different elements in the model. This interaction is a part of dynamic behavior of the system.

This interactive behavior is represented in UML by two diagrams known as Sequence diagram and Collaboration diagram. The basic purpose of both the diagrams are similar.

Sequence diagram emphasizes on time sequence of messages and collaboration diagram emphasizes on the structural organization of the objects that send and receive messages.

Purpose of Interaction Diagrams

The purpose of interaction diagrams is to visualize the interactive behavior of the system. Visualizing the interaction is a difficult task. Hence, the solution is to use different types of models to capture the different aspects of the interaction.

Sequence and collaboration diagrams are used to capture the dynamic nature but from a different angle.

The purpose of interaction diagram is −

  • To capture the dynamic behaviour of a system.

  • To describe the message flow in the system.

  • To describe the structural organization of the objects.

  • To describe the interaction among objects.

How to Draw an Interaction Diagram?

As we have already discussed, the purpose of interaction diagrams is to capture the dynamic aspect of a system. So to capture the dynamic aspect, we need to understand what a dynamic aspect is and how it is visualized. Dynamic aspect can be defined as thesnapshot of the running system at a particular moment

We have two types of interaction diagrams in UML. One is the sequence diagram and theother is the collaboration diagram. The sequence diagram captures the time sequence ofthe message flow from one object to another and the collaboration diagram describes theorganization of objects in a system taking part in the message flow.

Following things are to be identified clearly before drawing the interaction diagram

  • Objects taking part in the interaction.

  • Message flows among the objects.

  • The sequence in which the messages are flowing.

  • Object organization.

Following are two interaction diagrams modeling the order management system. The first diagram is a sequence diagram and the second is a collaboration diagram

Types of messages in sequence diagram software

The Sequence Diagram

The sequence diagram has four objects (Customer, Order, SpecialOrder and NormalOrder).

The following diagram shows the message sequence for SpecialOrder object and the same can be used in case of NormalOrder object. It is important to understand the time sequence of message flows. The message flow is nothing but a method call of an object.

Describe The Different Types Of Messages In Sequence Diagrams

The first call is sendOrder () which is a method of Order object. The next call is confirm () which is a method of SpecialOrder object and the last call is Dispatch () which is a method of SpecialOrder object. The following diagram mainly describes the method callsfrom one object to another, and this is also the actual scenario when the system is running.

The Collaboration Diagram

The second interaction diagram is the collaboration diagram. It shows the object organization as seen in the following diagram. In the collaboration diagram, the method call sequence is indicated by some numbering technique. The number indicates how themethods are called one after another. We have taken the same order management system to describe the collaboration diagram.

Types Of Messages In Sequence Diagram Design

Method calls are similar to that of a sequence diagram. However, difference being the sequence diagram does not describe the object organization, whereas the collaboration diagram shows the object organization.

To choose between these two diagrams, emphasis is placed on the type of requirement. If the time sequence is important, then the sequence diagram is used. If organization is required, then collaboration diagram is used.

Where to Use Interaction Diagrams?

What Is Message In Sequence Diagram

We have already discussed that interaction diagrams are used to describe the dynamic nature of a system. Now, we will look into the practical scenarios where these diagrams are used. To understand the practical application, we need to understand the basic natureof sequence and collaboration diagram.

The main purpose of both the diagrams are similar as they are used to capture the dynamic behavior of a system. However, the specific purpose is more important to clarify and understand.

Sequence diagrams are used to capture the order of messages flowing from one object to another. Collaboration diagrams are used to describe the structural organization of the objects taking part in the interaction. A single diagram is not sufficient to describe the dynamic aspect of an entire system, so a set of diagrams are used to capture it as a whole.

Interaction diagrams are used when we want to understand the message flow and the structural organization. Message flow means the sequence of control flow from one object to another. Structural organization means the visual organization of the elements in a system.

Interaction diagrams can be used −

  • To model the flow of control by time sequence.

  • To model the flow of control by structural organizations.

  • For forward engineering.

  • For reverse engineering.