I know a dependency relationship is depicted using a striped arrow e.g.:
Client -----<<create>>----> Server
I see that multiplicity is typically needed for other relationships (association, composition, aggregation) however, I'm unsure if it's needed or required for a dependency relationship. Should I put a '1' on each side of the above diagram?
No, there's no point in multiplicity on a dependency. Dependency merely states that a classifier (usually a class) in some way depends on another classifier. There is no way to say you depend on specific amount of those other classifiers since it doesn't touch the instances level.
In the UML specification (Section 7.5.1.) we have:
Types and multiplicity are used in the declaration of Elements that contain values, in order to constrain the kind and number of values that may be contained.
As association (including its stronger versions shared and composite aggregation) is semantically equivalent to a classifier's feature it support multiplicity. But this is not applicable to dependency.
Of the types of relationships in Class diagrams, multiplicity doesn’t apply to generalisations and realisations. You can apply multiplicity to dependencies but it often is not useful to do so, since dependencies are about how changes to one thing impact another.
Related
I'm working on a project where I'm using an SDK that provides things I need via some classes. I've named these ProviderProvider and Provider, that grant access to OneThing that is an IThing.
An example is shown here
.
My question is: What is the correct (or best) way to show that the Model provides the list of OneThings to the View through those classes?
Do you show this explicitly as in my example, by drawing a dependency arrow from Model to OneThing? That doesn't seem right to me and quickly becomes visually cluttered.
Do you not explicitly define that relationship, but is it simply implicitly defined through the other relationships?
Do you define that relationship semi-explicitly through attributes, notes or some other way?
What relations and attributes should I add/remove specifically and why?
You already have the implicit relationship since you use this class as a type of data returned by Model so you do not need to add that relationship explicitly.
It may be useful though, especially for classes that are core in the system, to add a diagram with dependencies only. Then you don't care about relationships between other classes, you only show on one diagram all classes that depend on the core one (it may be even more than one diagram).
One hint - in Case tool (like EA) even if you don't intend to show the relationship on the diagram since it is indicated implicitly it is still good to create the explicit dependency and just remove the arrow. This will support the traceability through tools like traceability matrix or dependency tree.
I can't find answer for my question . Is there a limit to how much dependency reliationship can be between two classes ? Does UML class-diagrams in general can't have more than one reliationship of the same type between two classes but they can have 2 or more reliationship of different types (for example between two classes they both can have composition and generalization reliantionship ?
You can have many associations between two classes, as well as many dependencies. You should stereotype those dependencies to differentiate them.
In general the UML specification does not restrict how many relationships of a specific type can be between the same classes, but due to the logic and meaning of a relationship you can assume some limitations.
Generalization, realization have a meaning where if there exists this relationship between two classes, it directly implies some consequences. Repeating the same relationship for the second time will have no further impact so it doesn't make any sense. It's also hard to specialize further those relationships through stereotypes.
Simple dependency provide some information that again cannot be "repeated" by having next dependency. Yet stereotyped dependency can bring more value and information so you can have more than one of dependency but with different stereotypes. Once you have one dependency of specific stereotype repeating the same one doesn't provide additional value, yet another dependency of different stereotype is a fully understandable and reasonable case. In theory the same dependency could be applied twice in two different directions, but I would then investigate deeply - it is usually showing that there is something wrong with the project.
Associations (including aggregation - both shared and composite) between two classes can have many different meanings. They should be differentiated either by association name, association roles, stereotype or by mixing those methods. So you can have multiple associations of the same "type" between the same two classes and they will have significant meaning. So many associations between the same classes are absolutely OK and it is a typical situation.
Mixing different relationships are also absolutely OK, however sometimes one relationship implies other. In general any (or almost any) relationship imply non-stereotyped dependency (in the same direction) so using it explicitly doesn't give any additional information or effect.
There is no limit to how many dependencies can be between two classes. But you have to consider a couple of important moments. On the website https://vaughnvernon.co of a principal architect Vaughn Vernon I have found interesting comments about usage of UML dependencies:
While dependency may have a broad meaning, it is best not to overuse
the dependency relationship. In an analysis model class diagram such
as a domain model diagram, you may be tempted to convey that all the
classes just depend on each other. Interestingly, however, the
Rational Unified Process (RUP) specifies that the general class
relationship that should be used in the analysis model is association,
and not dependency. Therefore, even when you are modeling higher-level
concepts it is best not to use the dependency relationship loosely. It
is just too nebulous.
Further, unless you use the dependency relationship in a constrained
manner your model consumers (yourself or other developers) will simply
have too broad an interpretation of its meaning. Generally those
filling architect and designer roles in a project are there to give
guidance to less experienced developers. Thus the dependency
relationship should be used to convey a specific kind of guidance from
architects and designers to developers.
So what should a dependency relationship represent? In our UML example
above the dependency means that class A uses class B, but that class A
does not contain an instance of class B as part of its own state. It
also means that if class B’s interface changes it will likely impact
class A and require it to change. I suggest that you constrain your
use of dependency relationships to non-state related concerns. You
would use dependency to indicate that, for example, class A receives
an instance of class B as a parameter to at least one of its methods.
You would also use dependency to indicate that class A creates an
instance of class B local to one of its methods. You
would not, however, use dependency to indicate that class A declares
an instance variable of class B, as that would indicate a
state-related concern. Again, use association to do that.
I am making a structural diagram in UML using classes and objects and wondered if I was doing it correctly.
Would the following (on the right) be the correct way to represent an object diagram of the left-hand side class diagram?
No. You are using a Generalization which is not the case. Either leave that out or use a stereotyped dependency <<instanceOf>>. Note that this is no standard as per UML specs. But those specs leave you the freedom to express is this way.
The class from which the object is instantiated is already shown in the name objectName::className.
From Annex A p. 683 of the UML 2.5 specs, which describes the organization of diagram types:
NOTE. This taxonomy provides a logical organization for the various major kinds of diagrams. However, it does not preclude mixing different kinds of diagram types, as one might do when one combines structural and behavioral elements (e.g., showing a state machine nested inside an internal structure). Consequently, the boundaries between the various kinds of diagram types are not strictly enforced.
I found a definition for association in UML as below.
An "association" in UML is defined as a kind of relationship between
classes,which represents the semantic relationship between two or more classes that
involves connections (links) among their instances .
I am not clear what is semantic relationship. Can anyone explain it with example with comparing it with non semantic relationship?
Associations in plain text
An association is a semantic relationship. The UML clause means that there is a structural relationship between instances of the associated classes independently of any specific implementation. "Semantic" underlines that the relationship is between the instances themselves, and not just "accidentally" for an operation:
Use associations primarily where there are structural relationships among objects. Do not use them to show transient relationships such as parameters or local variables of procedures.- Booch, Rumbaugh & Jacobson in Unified Modeling Language User Guide, 2nd edition
More arguments
What is "semantic"?
The term "semantic" is borrowed from linguistics and refers to the meanings behind the words. Linguists and map words (e.g. "Car", "Driver") to their meaning (e.g. a real car, a real person), and analyze the relation between words with a view of this mapping:
So, applying this to UML (modelling language) if you'd have the classes Car and Driver, you CAN model the semantic relationship as an association between the two classes.
What is not semantic?
Not all relationships are of semantic nature. You can have dependencies, which can express a technical relationship:
a transient relationship during an operation: with a factory pattern for example, a DriverFactory would «create» a Driver instance. Both instances the factory and the driver are related only at the exact moment of the creation operation. But the two instances are completely independent the nanosecond after.The same applies if the implementation of an operation needs to create a local instance of another class. Both classes are not associated, since we could imagine another implementation that works without such an instance.
a structural dependency: Maybe an operation require some other classes as parameter. Since the parameters themselves are transient, there is no association. But nevertheless, teh class needs to know about the other class.
For the records, I'm grateful to this public domain contributor for the nice car and driver and to 18f for advice on inclusive communication.
The subject of Semantics is sense. If one thing has something that is connected by sense to another thing, it is the semantic relationship. That definition is terribly wide. And, applied to UML relationship, incorrect. It is incorrect for two reasons.
First, UML covers not only Class-Instance languages, such as Java or C++, but pure object languages with heredity created by Prototypes as well. And this second variant is not covered by your definition at all.
Second, in UML you can have class A connected to class B through some complex AssociationClass, that is shown by a box with arrows, not arrow only. And it still will be named an association and it IS a semantic relationship, too. But a the semantic relationship goes from A to B through two classes, it is still a semantic relationship, but it is not an association in UML.
If you are trying to be deep in subject, better read the UML documentation: "An Association classifies a set of tuples representing links between typed instances." (UML 2.5, pharagraph 11.5.1). Notice: ANY link between two instances can be shown as an association. Maybe the book you are reading is wholely not so bad, but in the very place that you have cited the author merely tries to use pretty words not understanding their meaning and not even trying to be understandable to readers and to be CORRECT.
A model says something about the things being modeled. This is its semantics. Almost all elements of UML have semantics, defined in the sections titled "semantics". One exception is the comment. Adding a comment to a model doesn't influence its meaning.
Then why does the UML say this explicitely about associations? The reason is, that an association may or may not say something about the structure. If it doesn't, it is purely semantic.
For example it could tell us, that a Car can have at most one Driver. It doesn't necessarily mean that the car has an attribute of type Driver.
If we want to model that the two associated classes own attributes typed by the other end of the association, the notation will show this by small dots on its ends. Many people are not familiar with this notation and interpret associations without a dot in the same way. However, without the dots attributes are owned by the association itself and the structure of the classes is not influenced.
By the way, a class being the type of a parameter of an operation or having a dependency also means a semantic relationship.
Are the relationships «use» and «include» same in use case diagrams?
«use» is NOT a standard element of use case diagram. But UML standard allows using foreign diagrams elements. So, you can formally use «use» element that normally belongs to class diagram elements and is a sort of Dependency. Its meaning is:
A Usage is a Dependency in which one NamedElement requires another
NamedElement (or set of NamedElements) for its full implementation or
operation. The Usage does not specify how the client uses the supplier
other than the fact that the supplier is used by the definition or
implementation of the client.
(Citation taken from UML 2.5 standard)
«include»
"is a DirectedRelationship between two UseCases, indicating that the
behavior of the included UseCase (the addition) is inserted into the
behavior of the including UseCase (the includingCase) It is also a
kind of NamedElement so that it can have a name in the context of its
owning UseCase. The including UseCase may depend on the changes
produced by executing the included UseCase. The included UseCase must
be available for the behavior of the including UseCase to be
completely described.".
(Citation taken from UML 2.5 standard)
So, both these two sorts of connections are very close in meaning, but are not the same technically.
Usage is applied to NamedElements and Including to Behaviours.
Incliding is a bit more powerful element - it can be NamedElement itself.
Their main difference IMHO is that Usage can describe implementation.
Also, Usage can connect an Including to some other NamedElement. Including cannot connect Usages. That difference is radical enough, but not very important, because of rare need of such connection.
Formally, you can use them both in Use case, but the real reason for it can happen rarely. The most realistic case is when you use some classes in Use Case diagram (it is allowed, too), and use «use» between them.
Of courses not, Usage («uses») and Include («include») are different meaning.
Usually, we do not use so much the Usage relationship on use case diagrams which means that an element requires another
In the other hand Include are used a lot and means that the source use case includes (always) the targeted use case.
«use» is obsolete in UML 2.0 (maybe even earlier), you should stick with «include» and «extend».