Just as Generalization in UML corresponds to Inheritance, what do Include & Extend relationships correspond to in OOP?
I do realize that Generalization represents a 'is-a' relationship. Would Include represent 'has-a' relationship?
There are no include or extend relationships in UML Class Diagrams. If you refer to Use Case Diagrams they have no direct representation on code level, as you do not implement a Use Case as a single artifact in your software.
AFAIK, include used in Use Case diagrams. It shows dependency between specific use case and common use case.
Example:
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Includes means direct dependency, which means that an including use case requires an including use case. Extension means extra functionality that you can add to a use case at a specified point.
An example of include relation is when you include a class in java. You must have the class for your code to execute, but this doesn't mean that you always call the other class.
An example of extends are eclipse extension points, which let you define new functionality for the eclipse platform at specified points, but the platform is unaware of the extensions.
Related
In the below UML diagram, Account has an aggregation of Orders. Based on most online resources, this would typically mean Account class has something similar to a List as an instance.
But in reality, for a real world web app with persistent storage, that is not usually how the Account Class would be. It won't have a list of orders as instance. Instead some other controller class will just query a datastore asking for all Orders belonging to an Account. So in a UML class diagram for such an app, is this still the right way to represent relations? The cardinality and maybe the concept of aggregation looks right from a database entity perspective. Just that the diamond makes no sense from a Class perspective.
Or should it show a DataStore/DataManager with a getOrdersForAccount() method and connect it to Account class and Orders class through a dependency relation (dotted line with arrow) ?
This depends on what you want to represent.
The class model you have already would be sufficient as a logical domain model, expressing the logical relationships between entities in your domain. This might not be how you implement your software in code precisely, but it will guide you (and others) in understanding the entities and their relationships without getting bogged down in that implementation detail. At this level, your diagram may have a few design choices (strong aggregation for example is arguably a design choice, but it may not be, as is the use of enumerations and keys) but not that many and nothing that really detracts from the underlying logic. If anything, you could loose some design choices here and improve the expression of logic.
What you may also want is to provide a representation of how the OO code is implemented physically as well. This would be an additional class diagram that shows more precisely the implementation detail. You will have far more design choices in this diagram -- whether to use a collection or not for orders (e.g. a list or some other collection type class), what your data access patterns are (Adapters, Managers, ORMs etc.). At this level you will most likely loose the strong aggregate notation, as at this level we are talking about classes referencing each other which is most simply denoted using basic associations. You might want to use arrows and/or dot-notation to indicate end ownership and reference directions so that it's more clear what the relationships between classes are.
So, I think your question is a classic question about levels of abstraction in models and analysis vs design. Thanks for asking it!
The aggregation just means: "if you delete the account you need to delete the orders as well".
I also recommend to just leave the aggregation away (for most cases) since it only adds little extra semantics to your model. In this case it seems obvious to delete the order when the account is deleted. The only thing the aggregation added here is (as in most cases) some confusion or some futile discussions about the worth of that diamond.
If you have a domain where the filled diamond is used it should be documented in the modeling rules. When using the shared aggregation the documentation is even mandatory since there is no semantics per se in the specs (see box on p. 110 of UML 2.5).
It depends on how deep you want to go with UML design.
If you target code generation from UML then you probably need to add the class you mentioned.
It would look a lot like Registry Pattern:
UML Diagram
You can add abstraction so you can change implementation of your DataManager (if your DataManager is third-party then just call the API from DataManagerImplementation).
After that, depending on your implementation, once you have the list, if you need to keep it then add the association Account -> Order, if you can live with the list on the stack then you are good to go.
C++ instanciation example:
DataManagerImplementation *db = new DataManagerImplementation();
// Dependency injection
Account *acc = new Account(db);
Then in 'Account' class:
Account::Account(DataManager *db)
{
// Fetch list at creation
// Here 'orders' could be a member
m_db = db;
vector<Order*> *orders = m_db->GetOrders(this);
}
PS: I also recommend to put arrow (direction) on association/aggregation, otherwise it implies that the association is bi-directional and so that account has a pointer to an order list, and every order also has a pointer to an account, and I am not sure this is needed.
To edit PlantUML: http://www.plantuml.com/plantuml/png/SoWkIImgAStDuN99B4dqJSnBJ4yjyimjo4dDJSqhIIp9pCzJqDMjiLFmBqf9BK9ImuKk05Hcfw2afGHHYIbjfL2McboINsG3bj6oKz1oJoq1iuir79EJyqlpIZIve0m5a566IfYMEgJcfG0T2m00
I am designing a class diagram for an assignment. In this design, I use a separate class called Currency, to define currency values and their functionality. there are at least four other classes have to use this Currency class.
How can I show it in the class diagram ? I mean, do I need to draw relationships (connecting lines) from the Currency class to all the others ?
Is there a better way ?
What am I doing wrong here ?
There is nothing wrong and a reusability of a class is valuable. Actually that's a standard situation.
If you use this class in another class as an attribute you have two options to depict that:
draw an association relationship (line) from the class using to the class that is used.
put the attribute in a proper compartment of a class that is using and as a type of an attribute (after a colon) put the name of the used class.
The benefit of the first approach is that you immediately see the dependency between the classes.
If you use a class but not directly as an attribute type you use other relationship types that suit best to the situation you want to describe.
As I imagine one of your concerns is that you'll have a lot of relationships pointing to your class (in your case Currency). Don't worry about that. You don't have to put everything in a single diagram. Put a full specification of your class on one diagram with those relationships where it uses something else and then put only the class box with a name (without any compartment) on diagrams defining those elements that use your class. It will make your model readable. And with a support of some CASE tool you will be able to see all relationship and dependencies of this class anyway. By the way that's how the UML specification is written. Look for example how Namespace is used in the diagrams there (and many others as well).
Of course I'm not suggesting creating one diagram per one element to define it. No. Collect them in logical Packages (hey - that's exactly what Packages are for!) and make a class diagram per Package. If the Package becomes too large - you might need to split it into smaller subpackages.
For Currency your Package would be probably something like Utils. It can also contain other elements like Date, Address etc. Note - these are typical examples, probably every analyst/designer/programmer sooner or later has to cope with those elements. If you build them well, you'll be really able to reuse them in future applications as well.
One last thought. While you build "package based" Class diagram you might also need a diagram that shows just specific parts coming from several Packages to clarify some bit of your system/business/whatsoever. This is also absolutely fine. Again a benefit of CASE tool here is that it keeps consistency in your model.
Is the arrow read like "Arena depends on LeagueStore" ? How is this implemented ? Here is a similar question, but it doesn't include such an arrow.
picture taken from slide 9
The UML relationship "depends on" is deliberately wide in scope. It means that some aspect of the "classifier" (class, interface, package, ...) referenced by the relationship is used by the classifier at the other end of the relationship. This can include calling a method, using a type, including a package and so on.
In this case I think it can clearly be interpreted as "uses", that is, calls one or more of its methods. Today, this relationship has its own UML representation as a stereotype called "uses" on the dependency relationship to make it a little more specific.
The diagram is not a very good example of a bridge. The name comes from the whole idea that there are two hierarchies connected at the top. All this diagram is depicting is the fact that the outer class (Arena) manipulates the LeagueStore through an outer class. That's not even a pattern, that's the Envelope-Letter Idiom from Coplien's Advanced C++.
Bridge would be LeagueStore having a delegate inside (impl, as depicted), but then also having specializations of LeagueStore. For example, if you had a class called Report, it would have ReportImpl inside, that could have subclasses like JasperReport and BirtReport, but then Report could have subclasses like CrosstabReport.
I'm doing an UML diagrams for a project but I have a doubt...
I use an example to explain:
public class Book{...}
public class Library{
private ArrayList<Book> books;
public void insert(Book b){...}
public Book get(Book b){...}
}
In this case between Book and Library there's an aggregation but also a dependency, right?
Aggregation is a relation in which the "parent" class contains the "child" class, instead the dependency is the case in which a class use another class by parameter or return type.
Now, if a class A contains object of another class B mean that the B's object has been passed in some way at the object of class A, the only way is using a method(or a constructor), so the aggregation involves the dependency?
P.S.: sorry for my poor english
With all due respect to your professor, I disagree. You do have aggregation in your diagram, since Library contains Books (both semantically and syntactically).
A UML dependency relation means that "some UML element or a set of elements requires, needs or depends on other model elements for specification or implementation" (from my favorite UML reference site: uml-diagrams.org). When you put an aggregation link between two elements, it is already stated that one depends on the other, therefore adding a dependency relation between them is redundant.
I am no UML expert, but one thing I've really liked in "UML in a Nutshell" was a sentence saying that UML is useful only when it's intuitive for everybody.
Having said that, I'd suggest not over-complicating your diagrams. Not everything can nor has to be presented in a diagram. In your case the Library has some Books, a case of aggregation/composition (depending on other details not mentioned in your description). You dont have to state a dependency between these two classes, because the aggregation implies it. In my understanding a "dependency" is useful when you want to state an indirect relationship, a runtime dependency for instance.
Or the "extends" is a use case inheriting another?
--update
Just a clarification, I've read books and made a lot of diagrams. But I just can't see any difference between extends on UML and on inherance. As Bill said, UML extends indicates optional behavior, but in inherance either you get new behavior you can or not use. So, what's the difference?
I think in UML the difference is in that "extends" is based on extension points, which means there has to be a named point in the use case where the extension will be applied. The semantics are not very precise about this. Inheritance for use cases means changing some behaviour, not exzactly specifying where.
Another important point is about the inheritance and the Liskov substitution principle. You should be able to use one use case, which inherits from another, in any place you can use the another one. This does not hold for the way "extends" is understood. When one use case is extended by another, it means that one might be modified by another, but still it contains the main scenario path, which might be forked and joined by the extending use case. This is, I think, about the difference between structural and behavioural inheritance. Inheritance is about achieving the same goal and satisfying the same interests - same responsibility and behaviour constraints, where extension is about modification of the structure of the path of scenario, which might be triggered by additional interests - like error checking.
Inheritance actually is not a very good mechanism to be used for use cases, combined with actor inheritance, which makes more sense, it can lead to unwanted paradoxes. Following the advice of Alistair Cockburn (Writing effective Use Cases), inheritance should be used only for expressing variations in technical details or data formats for a particular use case.
This is very similar to inheritance. See a detailed description of this concept here.
Enjoy!
In the tool I use in my company we have modeling restrictions.
Inheritance:
From Actor to Actor, from UseCase to Usecase, from System to System. You can't have other inheritances in your diagram because I got a forbidden sign.
Extend can only be done between two Usecases and not between other elements.
I don't really see the difference between inheritance and extends between two usecases.
I will keep on reading the next posts because after reading all answers I still don't understand:-)
Extends is used to add additional, optional, behavior to the use case that is being extended, but does not change any of the behavior in the base use case.
An inheriting use case would replace one or more of the behaviors of the inherited use case. In other words changing the behavior of the base use case, rather than simply adding new functionality. Note that use case inheritance is not quite the same as class inheritance.
See this article.