Class diagram - Wikipedia
CS Home Data Modeling ERD Entities Relationships Attributes Example sexygf.info It is a graphical representation of data requirements for a database. class (parent) is related to multiple entity instances in another entity class (child). In UML modeling, a relationship is a connection between two or more UML model elements that adds semantic information to a model. There are also many-to-many and one-to-one relationships; as you can see pattern for the many-to-many relationship, and shows the UML class diagram.
Generalization relationships appear in class, component, and use-case diagrams. Interface realization An interface realization relationship is a specialized type of implementation relationship between a classifier and a provided interface. The interface realization relationship specifies that the realizing classifier must conform to the contract that the provided interface specifies.
Include An include relationship between use cases specifies that an including or base use case requires the behavior from another use case the included use case. In an include relationship, a use case must use the included use case.
Manifestation A manifestation relationship shows which model elements, such as components or classes, are manifested in an artifact. The artifact manifests, or includes, a specific implementation for, the features of one or several physical software components. Note attachment A note attachment relationship connects a note or text box to a connector or shape. A note attachment indicates that the note or text box contains information that is relevant to the attached connector or shape.
Object flow An object flow is a type of activity edge that models the flow of objects and data from one activity node to another.
Realization A realization relationship exists between two model elements when one of them must realize, or implement, the behavior that the other specifies.
The model element that specifies the behavior is the supplier, and the model element that implements the behavior is the client.
From the above description, we can extract the following sentences which focus on the constraints that will need to be modeled. Each Order must contain one and at most many Products. The rest tells us that an order can contain many products.
Each Product may be contained in many Orders. Of course, we need to allow a product to be in many orders. There are significant differences in this modeling problem compared to what we have seen before; these are listed below. The maximum multiplicity i. We will see how to model this in UML and then how to map this to the relational model.
There are two attributes described, the sale price and the quantity of the product being ordered, that cannot possibly be attributes of either the Products or Orders classes. These attributes are a result of the association between the Order and the Product, they describe each individual instance of the association.
Below, we learn how to model such attributes in UML and then how to implement these in the relational model. Class diagram The many-to-many relationship will be modeled with an association that specifies a many cardinality in the multiplicity constraints of both ends of the association. UML gives us a way to model relationship attributes by showing them in an association class that is connected to the association by a dotted line.
Design pattern: many-to-many (order entry)
This is shown in the figure below with the OrderLine association class and the two attributes quantity and unitSalePrice as described above. If no information needs to be modeled about specific associations between objects such as the quantity and unitSalePricethen the UML class diagram omits the association class. Association classes can be attached to associations of different cardinalities, not just many-to-many associations as is the case with OrderLine.
Sales database UML class diagram. Other views of this diagram: We need to know the subtotal for each order line that is, the quantity times the unit sale price and the total dollar value of each order the sum of the subtotals for each line in that order.
In fact, they could be stored. The reader should consider the advantages and disadvantages of whether or not to store derived attributes in the database. So for every many-to-many association, we will need an additional table, a junction table, in the database that will store all the relationship instances.
Association[ edit ] Class diagram example of association between two classes An association represents a family of links. A binary association with two ends is normally represented as a line. An association can link any number of classes. An association with three links is called a ternary association. An association can be named, and the ends of an association can be adorned with role names, ownership indicators, multiplicity, visibility, and other properties.
There are four different types of association: Bi-directional and uni-directional associations are the most common ones. For instance, a flight class is associated with a plane class bi-directionally. Association represents the static relationship shared among the objects of two classes.
Aggregation[ edit ] Class diagram showing Aggregation between two classes. Here, a Professor 'has a' class to teach.
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Aggregation is a variant of the "has a" association relationship; aggregation is more specific than association.
It is an association that represents a part-whole or part-of relationship. As shown in the image, a Professor 'has a' class to teach.
from class diagram to database relational diagram - Stack Overflow
As a type of association, an aggregation can be named and have the same adornments that an association can. However, an aggregation may not involve more than two classes; it must be a binary association. Furthermore, there is hardly a difference between aggregations and associations during implementation, and the diagram may skip aggregation relations altogether. The contents of the container still exist when the container is destroyed. In UMLit is graphically represented as a hollow diamond shape on the containing class with a single line that connects it to the contained class.
The aggregate is semantically an extended object that is treated as a unit in many operations, although physically it is made of several lesser objects. Here the student can exist without library, the relation between student and library is aggregation.