I was wondering how we present a class that has both a "has-a" and "is-a" relationship with another class in a UML diagram.
I am wondering if this is correct:
A realize relation is used to either an <<interface>> or to an abstract class. So you would design it like this:
N.B.: The triangle from the realization must not overlap the class but touch it. Also there's likely a typo: seal instead of sell.
Simply use two relationships - one showing a generalization and a second showing association/shared aggregation/composite aggregation.
Below is an example with composite aggregation.
In case of association the method you suggested is an alternate notation having exactly the same semantics. You only need to use solid line not dashed for generalization as in my example. Dashed line depicts realization and points to an interface or any other specification that is implemented by class on the other end of realization arrow.
Related
I have class Controller in my java project, which has method like this:
As you can see, in the first line I am getting Singleton instance of ActualModes class and call method getActualModes().
So the first question is, which relatinship I should use in class diagram.
After that I am creating new instane of ModeContext class and then call method executeStrategy. In this case, which relatiship is better ?
It should be like this:
Access to the singleton (note the stereotype which is just convenient and no obligation or general standard) is anonymous and so you just have a dependency. The ModeContext in contrast uses a private (I don't know the scoping rules of the language you used, so I made it pivate) property called context. Note the dot which is saying exactly that.
Disclaimer: UML does not specify a mapping between Java and UML, so every answer to your question is open for debate.
I think both relationships are dependencies, drawn as dashed arrows from Controller to ActualModes and from Controller to ModeContext. The definition of 'dependency' according to the UML 2.5 specification (§7.8.4.1) is:
A Dependency is a Relationship that signifies that a single model Element or a set of model Elements requires other
model Elements for their specification or implementation.
An example of a type of relationship which is in my opinion less suited, is the association, although its definition (§11.5) is quite broad:
An Association classifies a set of tuples representing links between typed instances. (...) An Association specifies a semantic relationship that can occur between typed instances.
One could argue that there are links between Controller and the other two classes, in the form of variables, but these variables are local method variables, which exist only temporarily during the execution of the method. Associations represent more durable links, e.g. class members - as far as I understand UML and as far as I have seen associations used in practice.
When creating relationships in an Object Class Diagram for an Object Relational Database, should the diamonds on the ends of the relationship links be filled in or not.
Here is an image of my Class diagram:
http://canning.co.nz/Weltec/Class_Diagram.png
It's a choice between Composition and Aggregation, which Wikipedia explains quite well.
In practice though, I think a valid answer is to just not worry about the difference, unless it's a school assignment. I've found that trying to make very detailed UML diagrams isn't terribly useful in practice.
Composition relationship has a coloured diamond shape structure ending at a class if it belongs to a 'is a' relationship (i.e- the entity cannot exist without the parent class) whereas the aggregation has an empty diamond shape ending at a class if it belongs to a 'has a' relationship (i.e- the entity can exist without the existence of the parent class.
A full diamond denotes Composition, or a 'owns' relationship. You use it when the referenced entity can't exist without the class representing it. An example would be order to order item. The order item just doesn't make sense without the order.
An empty diamond denotes Aggregation, or a 'has' relationship. A quick glance at your diagram makes me think this is the correct diagram element to use in your case.
But I agree with #mpartel: If there aren't any specific requirements to distinguish between the two just ignore the diamonds.
hi every body i'm trying to understand UML but there are some questions about it
In UML what is the significance of tagging a class with the stereotype <<abstract>>?
and how to express this constraint as an invariant,
A stereotype "abstract" does not exist - an abstract class should be depicted using italic font. Abstract means that a class cannot be instantiated. It needs a subclass to do so. So as a pseudo-code constraint this would mean
for all instances i of MyAbstractClass holds: i.actualClass != MyAbstractClass
or in ocl for MyAbstractClass holds
self.allInstances()->forAll(i: MyAbstractClass | i.classifier <> self)
As the word 'abstract' was not displayed in your first question version, I expanded on stereotypes in general:
First of all: When learning UML, stereotypes should not be the first things you look into. They are rather complex.
Stereotypes or keywords (both denoted with <<MyStereotype>>) do not have a general meaning. It is defined by the specific stereotype. Commonly you cannot express a stereotype as an invariant instead.
But some other aspects of UML can be shown the same way: A class from the UML Metalevel is marked with <<metaclass>> even though it does not have a stereotype or even is of different actual type. The Stereotypes themselves are shown with a <<stereotype>> marker (even if they are instances of a special class).
An example for a custom stereotype could be "Service". You could mark classes with it which represent a Service. There could be a constraint which tells you that a "Service" must implement a special Interface. In this case you could express this constraint as a (boring) invariant. But probably it is even just a marker. In the latter case you can use a keyword as replacement.
I realize this thread is a couple of years old, but I came to it when it was referenced by someone else, as supporting the assertion that the «abstract» stereotype isn't supported by the UML spec. That assertion isn't quite accurate, and I'd like to explain why. I'll start by clarifying what abstract classes are.
Abstract classes are definitions of classes that don't include complete implementation. Therefore, abstract classes can't be directly instantiated; they have to be specialized (inherited). Abstract classes are notated by italicizing the class name and the methods that are abstract, and additionally by optionally adding an {abstract} property to the class name and/or to the operations (methods, we usually say, but methods are actually the "method" by which the operation is implemented) that are abstract.
Interfaces are actually a specific type of abstract class: a class with zero implementation. Their notation is different from other types of abstract classes (don't italicize, use the «interface» keyword, and notate all the specialization arrows with dotted lines). So, as Christian says here, there is standard notation for abstract classes--at least, there is in class diagrams.
Now, while it is true, as Christian also says, that the «abstract» stereotype doesn't exist, it is also true that you can create it if you want to, and that doing so is supported by the UML spec. It's unlikely that you'll have a reason to (at least in class diagrams), but you still can.
A stereotype is an "extensibility mechanism" for UML (there are three: stereotypes, tagged values, and constraints). It allows you to more specifically define some sort of element. Stereotypes are applied to classes (metaclasses actually, metaclasses are classes whose instances are also classes). A number of stereotypes are pre-defined "Standard Stereotypes" (in UML 1.4 they were called "Standard Elements"). Examples of these are «metaclass» (again, a class whose instances are also classes) and «file» (a physical file in the context of the system developed).
Stereotypes are a type of keyword. The spec (Superstructure 2.0, Annex B, p. 663) has this to say about keywords:
UML keywords are reserved words that are an integral part of the UML
notation and normally appear as text annotations attached to a UML
graphic element or as part of a text line in a UML diagram. These
words...cannot be used to name user-defined model elements where such naming would result in ambiguous interpretation of
the model. For example, the keyword “trace” is a system-defined
stereotype of Abstraction (see Annex C, “Standard Stereotypes”) and,
therefore, cannot be used to define any user-defined stereotype.
In UML, keywords are used for four different purposes:
To distinguish a particular UML concept (metaclass) from others sharing the same general graphical form...
To distinguish a particular kind of relationship between UML concepts (meta-association) from other relationships sharing the same general graphical form...
To specify the value of some modifier attached to a UML concept (meta-attribute value)...
To indicate a Standard Stereotype (see Annex C, “Standard Stereotypes”)...
Keywords are always enclosed in guillemets («keyword»), which serve as visual cues to more readily distinguish when a keyword is being used...In addition to identifying keywords, guillemets are also used to distinguish the usage of stereotypes defined in user profiles. This means that:
Not all words appearing between guillemets are necessarily keywords (i.e., reserved words), and
words appearing in guillemets do not necessarily represent stereotypes.
In other words, you can create any stereotype that you want, so long as it isn't a keyword. Since "abstract" is not a keyword, it follows that you can create an «abstract» stereotype.
In order to do so, however, you would have to go to some trouble, more trouble in UML 2.0 and above than in UML 1.4. UML 1.4 simply stated that a stereotype was an extension mechanism for the UML spec. One could simply define the stereotype, apply it to whichever part of the UML metamodel one wanted, and document the change. UML 2.0 wanted to formalize the relationship of a stereotype to a UML metaclass (any item on a UML diagram is a metaclass, and part of the UML metamodel). So, they came up with Profiles. This sample diagram shows how profiles work:
Now, that black arrow may look a bit strange, since you don't see it in any context but this one. UML 2.0 introduced the concept of an Extension, which it defines as "used to indicate that the properties of a metaclass are extended through a stereotype." This black arrow indicates an extension.
I'll quote Tom Pender (The UML Bible, Wiley Publishing, 2004) for an explanation of this diagram, since he does a better job than the spec (and I certainly can't improve on it):
It shows that a Component is extended by a Bean stereotype, which is required. The Bean stereotype is an abstract type, with two subtypes - Entity and Session. Each instance of Component, therefore, must be extended by an instance of either the Entity stereotype or the Session stereotype. Remember that a stereotype is a kind of class that can have properties - in this case, a Session stereotype has an attribute named state. This corresponds to a tagged definition whose value specifies the state of the Session. The tagged value is an enumeration, StateKind, which has either a stateless or stateful value.
The Component has a constraint on it, displayed in the note attached to the Component symbol, which states that a Component cannot be generalized or
specialized.
The diagram also shows that an Interface metaclass is extended by the Remote and Home stereotypes. The EJB package has a constraint, displayed in the note that sits in the package, that states a Bean must realize exactly one Home interface.
So, you can indeed use an «abstract» stereotype if you have reason to go to the trouble of creating it. The main reason that anyone might want to is to represent an abstract class in some place other than a class diagram.
Case A
Say you have 2 classes Model and Settings.
Settings contains nothing but public static constants used throughout the application. What type of relationship would you say these 2 classes have?
Case B Say you have a IntersectionManager singleton class that is being used by classes Road and Car to get some data out of it.
What is the name of "class uses class" relationship in UML?
Would you use the same relationships for both case A and case B?
What UML arrow would you use to demonstrate this relationship?
Well, you could use the "uses" relationship (dotted or dashed line, open arrow).
I found a nice and helpful overview at https://web.archive.org/web/20180722012752/http://usna86-techbits.blogspot.com/2012/11/uml-class-diagram-relationships.html
The regular black & solid association line in both cases. Optionally with arrows on either or both ends to illustrate the direction of usage.
For example, consider the following: There is a class "Text Group" which is a generalization of class "Text Object." Text Groups can contain one or more Text Objects or one or more Text Groups. How would I represent this in UML? Any relevant links?
Thanks!
Think you want the Composite Pattern.
hth.
I think that u just composite it like it was any other class.
Generalisation shows the relation in inheritance tree between the parent and child classes. If you want to show containment, use composition or aggreagation relationship. As mentioned above, Composite design pattern is a perfect fit for your problem. You use compostion with an interface, which you implement with both the node and leaf classes in your composition hierarchy.
Classes are not restricted to a single relationship, and can be self referencing. You can draw both a generalisation and a composition relationship.
However I would question your specification of "one or more" multiplicity in a self referencing class since that will require either a circular or infinitely recursive reference. "zero or more" would probably be more appropriate. I would also question the semantics of a single object being a type of group, sounds counter-intuitive perhaps.