I'm making a class diagram for my project documentation, and have come across this case. There are quite a few connections already in the diagram, and I would like to add on as little as possible. So I thought, if an (abstract) parent class has connections with some other class, it's children usually also keep up the same connection. Is it also the case with UML diagrams, or do I have to connect every chilren to the other class too?
Example image, of what I'm thinking would be possible:
Associations of a parent class with other classes are implicitly inherited by the subclasses. The inherited associations should not be drawn explicitly in the diagram.
It does not matter whether the parent class is abstract or not.
In your example diagram, Player and Enemy have associations with DrawingClass.
Be careful if you add multiplicities to the association ends. For example, if the association in your example is a 1:1 association, then each DrawingClass instance is connected either to a Player or to an Enemy (or, if Entity is not abstract, to a direct instance of Entity), not to both.
The abstract (not interface) class Entity having let say the attribute drawingClass to DrawingClass the inheriting classes Player and Enemy also inherit the attribute drawingClass, so you do not have to repeat that attribute in them
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Just a simple question: I'm working on a class diagram for a dynamic web site for my internship. I have an association between two classes (client and article), the relation is many to many.
Normally I have to add an association class between them, but I don't want to because the client can only read the article's writing on the web page, and he cannot post. Is it correct if I don't draw the association class on the diagram?
There is no need to add association class only due to many to many relationship. The association class is needed when you have an association that at the same time is also a class, i.e. has some properties on its own.
You can use simple association with any multiplicity on any of the ends including having * on both ends.
I've started using the website draw.io, I want to create a class diagram but I couldn't find how to create an association class, any help would be useful. Thanks.
draw.io is a drawing tool, not a UML tool.
As such you can simply draw two class shapes, connect them with an association shape, then draw a third class as you association class and then use an association shape to connect you association class to the association.
Then go into the properties of the last association shape and change the line style to dashed.
Now it looks like a valid UML Association class, but I think you should really opt for a real UML tool instead of a drawing tool when you want to do anything with UML. Using this tool is similar to writing Java with MS Word.
The accepted answer is far to be perfect. In Draw.io (now called Diagrams.net), you can connect two shapes (here classes) with a connector but you cannot connect two connectors together.
Consequently, with the given solution, it will look like an association class but the dashes will not be really adjusted :
And really worste, if you need to re-arrange your diagram, the association link will not move and you will have to re-adjust it manually :
So, as it is sadly not possible to have a 100% satisfying solution for an association class, another solution is to turn the association class as a regular class. Here in the example, the OrderLine class is associated with both Order and Product classes. It is worth to note the migration of the multiplicities. Refactoring a class association as such an association will ALWAYS lead to have a 1 multiplicity for the non-association classes (here Order and Product), and the original multiplicities will be moved to the association class (here OrderLine).
On Wikipedia, I'm reading that an association relationship is an instance level relationship so we are talking about the relationship between the objects of two classes.
When we actually draw a class diagram, why do we use association on the class elements or blocks rather than objects? And there are also class level relationships for which we again use class elements. Since we don't have any way to show if we are talking about objects or classes I find this confusing. For example: I've heard people saying "Associate these two classes" Doesn't that sound wrong?
Links are to Associations as Objects are to Classes.
A Class is an abstraction that describes many specific objects. Similarly, an Association is an abstraction that describes many links between objects.
So your statement
an association relationship is an instance level relationship
isn't strictly correct because it mixes the abstraction (Association Relationship) with the instances it represents.
hth.
In fact, when you associate two or more classes it is done thanks to two or more UML Properties.
These latter are the "ends" of your associations and are "instance" i.e. they are typed by classe.
So an association is created between two classes on a class diagram but between each classes and the association you have a UML property.
Hoping it sounds clear ...
When you are making a class diagram you are defining types. Suppose you have a class User and a class Account, you use an association between User and Account to say: User instances can have link(s) with Account instances at runtime.
So, you use classes and associations at type level (class diagram) to define what can be possible at runtime (instance level).
The object is actually the Class that has been created virtualy. So a class is the "static" version of an Object. So, when we speak of UML, we speak about classes and not object.
But correct me if I'm wrong!
In a UML class diagram I want to show the relationship between two classes where the second class is the type of a class variable in the first.
I've looked here but am still unsure which relationship I should be using.
I think it may be the Dependency relationship but I am unsure.
Which should I be using?
It sounds like a composition(has a) but would need to hear more about your diagram.
Can I improve my design on these 2 diagrams below? If so, how?
I am confused by the use of association classes in my diagrams. Should I use them?
Figure 1
Figure 2
For association classes, they make sense only if they represent associations with some behaviour and state. Look at Article'sSubject. It has nothing more than source, target and identity. You don't need a class for such a association, just use plain association, which has all those properties. There are more such unnecessary association classes in your diagrams. Another important thing when using association classes is that every instance of that association class should have unique source and target pair. For example Comment is not identifiable just by Article and User - one user may have man ycomments on one article and that is not allowed.
An association class is used to capture certain characteristics of an association between two classes. These characteristics do not belong to the classes being associated but instead belong to the relationship between the classes.