Class diagram - Wikipedia
Oct 9, In a class diagram, obviously you can't have classes just floating around; you need to see the relationship between them. Many have trouble. They show relationships between classes, objects, attributes, and operations. SmartDraw's class diagram libraries have all the appropriate class notations you . Classes can also have multiplicities. You don't often see this used, except in one case: singletons. When it comes to A having or containing or referencing B.
Each cell contains exactly one expression and one value, and these values and expressions are not shared with other cells. The diagram above suggests that, given a spreadsheet, we can locate all of the cells that it contains, but that we cannot determine from a cell in what spreadsheet it is contained.
Given a cell, we can obtain the related expression and value, but given a value or expression we cannot find the cell of which those are attributes. In perspectives and relationships where the role names are attribute names, we would not have a role name for an un-navigable direction of an association. Hence, we have no role name naming the cell related to a value or expression.
Navigability and Perspectives Navigability is probably not useful in most conceptual diagrams.
For example, in a specification perspective, this defaults to In an implementation perspective, this would imply pointers in each object going to the related objects. This diagram suggests that cells are part of a spreadsheet and that an expression and a value are each part of a cell. Aggregation is almost never named and roles are only used if the attribute name would be unexpected.
There is a lot of variation in deciding when to use use aggregation. For example, experts might disagree on whether a Library can be represented as an aggregate of its Librarians and of its Patrons. Should This Be Aggregation? That would be OK in an implementation perspective i. I would not accept that in a domain or analysis model. This also captures the bi-directional navigability with a bit more elegance as well. Composition Example This diagram suggests that destroying a cell would also destroy its value and formula.
That makes sense if the cell does not share those components with other objects. However, destroying a spreadsheet does not necessarily destroy its cells. We can infer that because, if the cells have been cut or copied to the clipboard, the spreadsheet could be destroyed and yet the cells would remain available for pasting into some other spreadsheet.
This diagram indicates that a spreadsheet provides access to cells retrieved by cell name.
It suggests an eventual implementation by something along the lines of a map or table. A dependency is indicated by a dashed line ending at a navigability arrow head.
Relationships in class diagrams
Dependencies have little use outside of an implementation perspective. Dependency Example This diagram shows a system that has been decomposed into three major subsystems. The Model is the core data — the stuff that this program is really all about. The diagram on top shows Composition between two classes: A Car has exactly one Carburetor, and a Carburetor has at most one Car Carburetors may exist as separate parts, detached from a specific car.
Relationships in UML class diagrams
The diagram on bottom shows Aggregation between two classes: A Pond has zero or more Ducks, and a Duck has at most one Pond at a time.
The UML representation of a composition relationship shows composition as a filled diamond shape on the containing class end of the lines that connect contained class es to the containing class.
Differences between Composition and Aggregation[ edit ] Composition relationship 1. When attempting to represent real-world whole-part relationships, e.
When the container is destroyed, the contents are also destroyed, e. When representing a software or database relationship, e. When the container is destroyed, the contents are usually not destroyed, e. Thus the aggregation relationship is often "catalog" containment to distinguish it from composition's "physical" containment.
In practice, means that any instance of the subtype is also an instance of the superclass. An exemplary tree of generalizations of this form is found in biological classification: The relationship is most easily understood by the phrase 'an A is a B' a human is a mammal, a mammal is an animal. The UML graphical representation of a Generalization is a hollow triangle shape on the superclass end of the line or tree of lines that connects it to one or more subtypes.
The generalization relationship is also known as the inheritance or "is a" relationship.
c++ - How to show a Singleton relationship in a class diagram - Stack Overflow
The superclass base class in the generalization relationship is also known as the "parent", superclass, base class, or base type. The subtype in the specialization relationship is also known as the "child", subclass, derived class, derived type, inheriting class, or inheriting type. Note that this relationship bears no resemblance to the biological parent—child relationship: A is a type of B For example, "an oak is a type of tree", "an automobile is a type of vehicle" Generalization can only be shown on class diagrams and on use case diagrams.
The UML graphical representation of a Realization is a hollow triangle shape on the interface end of the dashed line or tree of lines that connects it to one or more implementers. A plain arrow head is used on the interface end of the dashed line that connects it to its users. In component diagrams, the ball-and-socket graphic convention is used implementors expose a ball or lollipop, whereas users show a socket.
Realizations can only be shown on class or component diagrams. A realization is a relationship between classes, interfaces, components and packages that connects a client element with a supplier element.
One class depends on another if the independent class is a parameter variable or local variable of a method of the dependent class. This is different from an association, where an attribute of the dependent class is an instance of the independent class. Sometimes the relationship between two classes is very weak. They are not implemented with member variables at all.How to draw Class Diagram in StarUML
Rather they might be implemented as member function arguments. Multiplicity[ edit ] This association relationship indicates that at least one of the two related classes make reference to the other.
This relationship is usually described as "A has a B" a mother cat has kittens, kittens have a mother cat.