Umbrello UML Modeller Handbook

Use Case Diagrams describe the relationships and dependencies between a group of Use Cases and the Actors participating in the process.

It is important to notice that Use Case Diagrams are not suited to represent the design, and cannot describe the internals of a system. Use Case Diagrams are meant to facilitate the communication with the future users of the system, and with the customer, and are specially helpful to determine the required features the system is to have. Use Case Diagrams tell, what the system should do but do not — and cannot — specify how this is to be achieved.

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Umbrello UML Modeller showing a Use Case Diagram

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Class Diagrams show the different classes that make up a system and how they relate to each other. Class Diagrams are said to be “static” diagrams because they show the classes, along with their methods and attributes as well as the static relationships between them: which classes “know” about which classes or which classes “are part” of another class, but do not show the method calls between them.

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Umbrello UML Modeller showing a Class Diagram

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Class

A Class defines the attributes and the methods of a set of objects. All objects of this class (instances of this class) share the same behaviour, and have the same set of attributes (each object has its own set). The term “Type” is sometimes used instead of Class, but it is important to mention that these two are not the same, and Type is a more general term.

In UML, Classes are represented by rectangles, with the name of the class, and can also show the attributes and operations of the class in two other “compartments” inside the rectangle.

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Visual representation of a Class in UML

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Attributes

In UML, Attributes are shown with at least their name, and can also show their type, initial value and other properties. Attributes can also be displayed with their visibility:

• + Stands for public attributes

• # Stands for protected attributes

• - Stands for private attributes

Operations

Operations (methods) are also displayed with at least their name, and can also show their parameters and return types. Operations can, just as Attributes, display their visibility:

• + Stands for public operations

• # Stands for protected operations

• - Stands for private operations

Templates

Classes can have templates, a value which is used for an unspecified class or type. The template type is specified when a class is initiated (i.e. an object is created). Templates exist in modern C++ and will be introduced in Java 1.5 where they will be called Generics.

Class Associations

Classes can relate (be associated with) to each other in different ways:

Generalisation

Inheritance is one of the fundamental concepts of Object Orientated programming, in which a class “gains” all of the attributes and operations of the class it inherits from, and can override/modify some of them, as well as add more attributes and operations of its own.

In UML, a Generalisation association between two classes puts them in a hierarchy representing the concept of inheritance of a derived class from a base class. In UML, Generalisations are represented by a line connecting the two classes, with an arrow on the side of the base class.

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Visual representation of a generalisation in UML

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Associations

An association represents a relationship between classes, and gives the common semantics and structure for many types of “connections” between objects.

Associations are the mechanism that allows objects to communicate to each other. It describes the connection between different classes (the connection between the actual objects is called object connection, or link.

Associations can have a role that specifies the purpose of the association and can be uni- or bidirectional (indicates if the two objects participating in the relationship can send messages to the other, of if only one of them knows about the other). Each end of the association also has a multiplicity value, which dictates how many objects on this side of the association can relate to one object on the other side.

In UML, associations are represented as lines connecting the classes participating in the relationship, and can also show the role and the multiplicity of each of the participants. Multiplicity is displayed as a range [min..max] of non-negative values, with a star (*) on the maximum side representing infinite.

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Visual representation of an Association in UML

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Aggregation

Aggregations are a special type of associations in which the two participating classes don't have an equal status, but make a “whole-part” relationship. An Aggregation describes how the class that takes the role of the whole, is composed (has) of other classes, which take the role of the parts. For Aggregations, the class acting as the whole always has a multiplicity of one.

In UML, Aggregations are represented by an association that shows a rhomb on the side of the whole.

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Visual representation of an Aggregation relationship in UML

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Composition

Compositions are associations that represent very strong aggregations. This means, Compositions form whole-part relationships as well, but the relationship is so strong that the parts cannot exist on its own. They exist only inside the whole, and if the whole is destroyed the parts die too.

In UML, Compositions are represented by a solid rhomb on the side of the whole.

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Sequence Diagrams show the message exchange (i.e. method call) between several Objects in a specific time-delimited situation. Objects are instances of classes. Sequence Diagrams put special emphasis in the order and the times in which the messages to the objects are sent.

In Sequence Diagrams objects are represented through vertical dashed lines, with the name of the Object on the top. The time axis is also vertical, increasing downwards, so that messages are sent from one Object to another in the form of arrows with the operation name and optionally the actual parameter values.

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Umbrello UML Modeller showing a Sequence Diagram

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Messages can be either synchronous, the normal type of message call where control is passed to the called object until that method has finished running, or asynchronous where control is passed back directly to the calling object. Synchronous messages have a vertical box on the side of the called object to show the flow of program control.

Collaboration Diagrams show the interactions occurring between the objects participating in a specific situation. This is more or less the same information shown by Sequence Diagrams but there the emphasis is put on how the interactions occur in time while the Collaboration Diagrams put the relationships between the objects and their topology in the foreground.

In Collaboration Diagrams messages sent from one object to another are represented by arrows, showing the message name, parameters, and the sequence of the message. Collaboration Diagrams are specially well suited to showing a specific program flow or situation and are one of the best diagram types to quickly demonstrate or explain one process in the program logic.

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Umbrello UML Modeller showing a Collaboration Diagram

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State Diagrams show the different states of an Object during its life and the stimuli that cause the Object to change its state.

State Diagrams exhibit Objects as state machines or finite automata that can be in one of a finite set of states and that can change its state via one of a finite set of stimuli. For example an Object of type NetServer can be in one of following states during its life:

and the events that can cause the Object to change states are

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Umbrello UML Modeller showing a State Diagram

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Activity Diagrams describe the sequence of activities in a system with the help of Activities. Activity Diagrams are a special form of State Diagrams, that only (or mostly) contains Activities.

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Umbrello UML Modeller showing an Activity Diagram

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Activity Diagrams are similar to procedural Flux Diagrams, with the difference that all Activities are clearly attached to Objects.

Activity Diagrams are always associated to a Class, an Operation or a Use Case.

Activity Diagrams support sequential as well as parallel Activities. Parallel execution is represented via Fork/Wait icons, and for the Activities running in parallel, it is not important the order in which they are carried out (they can be executed at the same time or one after the other)

There are a few elements in UML that have no real semantic value for the model, but help to clarify parts of the diagram. These elements are

Text lines are useful to add short text information to a diagram. It is free-standing text and has no meaning to the Model itself.

Notes are useful to add more detailed information about an object or a specific situation. They have the great advantage that notes can be anchored to UML Elements to show that the note “belongs” to a specific object or situation.

Boxes are free-standing rectangles which can be used to group items together to make diagrams more readable. They have no logical meaning in the model.

Component Diagrams show the software components (either component technologies such as KParts, CORBA components or Java Beans or just sections of the system which are clearly distinguishable) and the artefacts they are made out of such as source code files, programming libraries or relational database tables.

Components can have interfaces (i.e. abstract classes with operations) that allow associations between components.

Deployment diagrams show the runtime component instances and their associations. They include Nodes which are physical resources, typically a single computer. They also show interfaces and objects (class instances).

If at any time you need to create a new model you can do this by selecting the New entry from the File menu, or by clicking on the New icon from the application toolbar. If you are currently working on a model which has been modified Umbrello UML Modeller will ask you if it should save your changes before loading the new model.

You can save your model at any time by selecting the option Save from the File Menu or by clicking on the Save button from the application toolbar. If you need to save your model under a different name you can use the option Save As from the File Menu.

For your convenience Umbrello UML Modeller also offers you the option to automatically save your work each certain time period. You can configure if you want this option as well as the time intervals in the Settings from Umbrello UML Modeller

For loading an already existing model you may select the option Open from the File Menu or click on the Open icon from the application toolbar. The most recently used models are also available under the submenu Open Recent in the File Menu to speed up access to your most frequently used models.

Umbrello UML Modeller can only work on one model at a time, so if you ask the program to load a model for you and your current model has been modified since the last time you save it, Umbrello UML Modeller will ask you whether your changes should be saved to prevent any loss of work. You can start two or more instances of Umbrello UML Modeller at any one time, you can also copy and paste between instances.

To create a new diagram in your model simply select the diagram type you need from the New submenu in the Diagram menu and give a name to it. The diagram will be created and made active, and you will immediately see it in the tree view.

Remember that Umbrello UML Modeller makes extensive use of context menus: you can also right mouse button click on a folder in the Tree View and select the appropriate diagram type from the New submenu in the context menu. Note that you can create Use Case Diagrams only in Use Case View folders, and the other types of diagram can only be created in the Logical View folders.

Should you need to remove a diagram from your model, you can do this by making it active and selecting Delete from the Diagram Menu. You can also achieve this by selecting Delete from the diagrams context menu in the Tree View

Since deleting a diagram is something serious that could cause loss of work if done by accident, Umbrello UML Modeller will ask you to confirm the delete operation before actually removing the Diagram. Once a diagram has been deleted and the file has been saved there is no way to undo this action.

If you want to change the name of an existing diagram you can easily do this by selecting the Rename option from its right mouse button menu in the Tree View.

Another way to rename a diagram is to do this via its properties dialogue, which you obtain by selecting Properties from its Context Menu or by double clicking on it in the Tree View.

One of the first things you will do when editing a new diagram is to insert elements into them (Classes, Actors, Use Cases, etc.) There is basically two ways of doing this:

To insert elements that already exist in your model, just drag them from the Tree View and drop them where you want them to be in your diagram. You can always move elements around in your Diagram using the Select Tool

The second way of adding elements to your diagram is by using the Work Toolbar's edit tools (note that this will also add the elements to your model).

The Work Toolbar was by default located on the far right of the application window, Umbrello UML Modeller 1.2 has moved this to the top of the window. You can dock it into other edge or have it floating around if you prefer. The tools available on this toolbar (the buttons you see on it) change depending on the type of diagram you are currently working on. The button for the currently selected tool is activated in the toolbar. You can switch to the select tool by pressing the Esc key.

When you have selected an edit tool from the Work Toolbar (for example, the tool to insert classes) the mouse pointer changes to a cross, and you can insert the elements in your model by single clicking in your diagram. Note that elements in UML must have a Unique Name. So that if you have a class in one diagram whose name is “ClassA” and then you use the insert Class tool to insert a class into another diagram you cannot name this new class “ClassA” as well. If these two are supposed to be two different elements, you have to give them a unique name. If you are trying to add the same element to your diagram, then the Insert Class is not the right tool for that. You should drag and drop the class from the Tree View instead.

You can delete any element by selecting the option Delete from its context menu.

Again, there is a big difference between removing an object from a diagram, and deleting an object from your model: If you delete an object from within a diagram, you are only removing the object from that particular diagram: the element will still be part of your model and if there are other diagrams using the same element they will not suffer any change. If, on the other hand, you delete the element from the Tree View, you are actually deleting the element from your model. Since the element no longer exist in your model, it will be automatically removed from all the diagrams it appears in.

You can edit most of the UML elements in your model and diagrams by opening its Properties dialogue and selecting the appropriate options. To edit the properties of an object, select Properties from its context menu (right mouse button click). Each element has a dialogue consisting of several pages where you can configure the options corresponding to that element. For some elements, like actors you can only set a couple of options, like the object name and documentation, while for other elements, like classes, you can edit its attributes and operations, select what you want to be shown in the diagram (whole operation signature or just operation names, etc) and even the colours you want to use for the line and fill of the class' representation on the diagram.

For most UML elements you can also open the properties dialogue by double clicking on it if you are using the selection tool (arrow). The exception to this is Associations, in which case a double click creates an anchor point. For associations you need to use the right mouse button context menu to get the properties dialogue.

Note that you can also select the properties option from the context menu of the elements in the Tree View. This allows you to also edit the properties for the diagrams, like setting whether the grid should be shown or not.

Even though editing the properties of all objects was already covered in the previous section, classes deserve a special section because they are a bit more complicated and have more options than most of the other UML elements.

In the properties dialogue for a class you can set everything, from the colour it uses to the operations and attributes it has.

Associations relate two UML objects to each other. Normally associations are defined between two classes, but some types of associations can also exist between use cases and actors.

To create an association select the appropriate tool from the Work Toolbar (generic Association, Generalization, Aggregation, etc.) and single click on the first element participating in the association and then single click on the second item participating. Note that those are two clicks, one on each of the objects participating in the association, it is not a drag from one object to the other.

If you try to use an association in a way against the UML specification Umbrello UML Modeller will refuse to create the association and you will get an error message. This would be the case if, for example, a Generalisation exists from class A to class B and then you try to create another Generalisation from Class B to class A

Right clicking on an association will show a context menu with the actions you can apply on it. If you need to delete an association simply select the Delete option from this context menu. You can also select the Properties option and, depending on the association type edit attributes such as roles and multiplicity.

Notes, Lines Of Text and Boxes are elements that can be present in any type of diagram and have no real semantic value, but are very helpful to add extra comments or explanations that can make your diagram easier to understand.

To add a Note or a Line Of Text, select the corresponding tool from the Work Toolbar and single click on the diagram where you want to put your comment. You can edit the text by opening the element through its context menu or in the case of notes by double clicking on them as well.