Someone could help me please?
I want to make a class diagram in UML, and I have CATEGORY class which can have SUBCATEGORIES and so on. How can I manage it in class diagram, thus in mysql database?
Thanks in advance
A hierarchy (or tree) of categories is modeled with a recursive one-to-many association, which associates the Category class with itself, as shown in the following diagram:
Such an Information Design Model can be transformed into an OOP Class Model and into an SQL Table Model, like so:
Notice how the superCategory column is designated as a foreign key referencing the categories table in the table model: by a UML dependency arrow stereotyped as «fk».
I hope you can figure out yourself how to code the SQL Table Model in an SQL Create Table statement.
p.s.: For more about how to model databases with UML CLass Diagrams seee https://stackoverflow.com/a/21394401/2795909
can any one tell how to get hibernate Many-To-Many mapping with different dto files means suppose there are student and teacher relationship in that i want -
1) Student Dto class
2) Teacher Dto class
3) Student_Teacher Dto class and in this class all mapping are there
is this possible and how to do it ??
You need to annotate collection attribute with #ManyToMany annotation on each of the entities. In your case you will want to annotate Student and Teacher entity. Student_Teacher table will be created automatically if you are using schema export or you can use #JoinTable to specify join table details. This join table will have all the mappings.
For more details I have tried to explain #ManyToMany mapping here in simple way.
I have a class A and it has data members of class B and class C which are composition relationships. As I am going to draw a composition relationship line from B to A and C to A, does this mean I cannot also include the data members within the class A "box" because the relationship is inferred from the composition relationship lines?
I ask because the data member variable names seem a good way to help understand the context and this cannot be represented if you omit the data members from the class A "box"??
I am not sure if there is a cast-iron rule in UML or whether I am free to choose. This is not for auto-generation of code- just human reading.
At least, in UML you can show a name of each property like a figure below.
According to UML specification, both representations of data members, visually depicted association/composition between two classes or in-class data member display) are equivalent. Here is an example (a little bit modified your case, to make it clearer):
Note that association end also show the scope and collection type (besides the name of course). col_B is defined ase private {ordered} collection (like array).
So, getting back to the formal side of UML spec... a, x, aa, col_b and m_c are all co called A's structural features (or properties). They can all be visually depicted using relationsips between the classes or inside the class itself. You can even show "int" data type as a class and link it using a composition!
Which way you will use is up to you, kind of matter of personal taste.
I always apply a simple rule - basic data types (int, boolean, date, string, etc) and their arrays are showed in the class itself, while the class and enumeration based properties are depicted by a relationship (example on the top).
As simple data types are clear and well known and does not have their own properties, I find it clear enough to show them in-class (diagram is simpler and smaller).
The complex data types (classes and enumerations) however typically have their own properties (data members, associations), even inheritances, and I want to make the class structure stand out on my diagarm.
You can use your own logic though.
In a class diagram you cannot model the same composition both showing the association and the attribute, because in the UML semantic that would mean your class has two composition :-)
If in your diagram you already have classes B and C, I suggest you opt for the association ("relationship lines") solution.
To better understand the context, you can put the roles on the association: this is equivalent to the name of your attributes.
Was asked the following question,
Class C inherits from class B, class B inherits from class A
Would you call this
(1) Multiple inheritance
(2) Polymorphism
(3) Aggregation
(4) Enumeration
Now I was unsure of this, so I said enumeration. Correct answer is polymorphism. I can sort of see why, but I am having trouble explaining this from OOP principles.
Also, when it comes to OOP, what would 3 and 4 indicate?
Thanks.
Aggregation means, that an Object of class A contains (and makes use of) an object of class B.
Enumeration denotes just a data type which can be given a finite (usually small) set of named values (to group "things" together).
Multiple Inheritance would mean for a class to have more than one ancestor simultaneously (like Class a extends Class b, Class c, Class d).
I understand the difference between aggregation and composition but I am struggling a bit with association. My current understanding is that an association exists between classes when ‘they use each other’, for example, one object is passed to the other during a method call. See also:
http://www.codeproject.com/Articles/330447/Understanding-Association-Aggregation-and-Composit
Both objects exist independently and, in contrast to aggregation, no object is a container class of the other. Does this mean that both objects MUST have a copy of the other(s) (e.g. 1:m relationship) or how else is the association ‘stored’. Any feedback would be very much appreciated.
From the UML Superstructure 2.4.1:
An association declares that there can be links between instances of the associated types. A link is a tuple with one value for each end of the association, where each value is an instance of the type of the end. (UML Superstructure, Page 37)
Nothing more, nothing less. and very vague. Because of this, it is also very hard to understand. What I defined (In a course I teach) is a hierarchy of links from dependency to composition where:
Dependency from A to B means that A uses B but indirectly (say by receiving instances of it and forwarding them to other objects).
Association from A to B means that A uses B directly, (for example by calling methods)
Aggregation from A to B means that B is part of A (semantically) but B can be shared and if A is deleted, B is not deleted. Note that this says nothing about how the "is part" is implemented.
Composition from A to B is like Aggregation, where B cannot be shared and if A is deleted, all of its aggregates (Bs) are deleted also.
Aggregation is an Association relationship where the Association can be considered the containing class 'Owning' the contained class, and the lifetime of that relationship is not defined.
Association is an 'Has-A' relationship.
Example:-
public class Person
{
private final Name name;
private Address currentAddress;
//...
}
In this case, the Person Has-A name and Has-A Address, so there is an Association between Person and Name, and Person and Address.
An association describes a relationship between instances of one or more classes. In the words of the UML Reference Manual, "Associations are the glue that holds together a system."
Aggregation is a form of association in which there is a "whole-part" relationship. You may say that if a class Airplane has a class Engine then this forms a "whole-part" relationship.
Aggregation
Let's set the terms. The Aggregation is a metaterm in the UML standard, and means BOTH composition and shared aggregation, simply named shared. Too often it is named incorrectly "aggregation". It is BAD, for composition is an aggregation, too. As I understand, you meant you understand "shared aggregation and composition".
From UML standard:
Precise semantics of shared aggregation varies by application area and
modeler.
I haven't found a word about that aggregation supposed multiplicity, for example.
Association.
A definition from UML 3.4.1 standard:
An association describes a set of tuples whose values refer to typed
instances. An instance of an association is called a link. A link is a
tuple with one value for each end of the association, where each value
is an instance of the type of the end.
Aggregated relationship is a subclass of Association.
Association is based on relationship. IT is the glue for models.
But your feelings didn't lie - as the shared aggregation is not strictly defined, there is also NO any strictly defined boundary between Association and Aggregated association. Authors of tools and modellers have to set it themselves.
Association
It represents a relationship between two or more objects where all objects have their own lifecycle and there is no owner. The name of an association specifies the nature of relationship between objects. This is represented by a solid line.
Let’s take an example of relationship between Teacher and Student. Multiple students can associate with a single teacher and a single student can associate with multiple teachers. But there is no ownership between the objects and both have their own lifecycle. Both can be created and deleted independently.
Aggregation
It is a specialized form of Association where all object have their own lifecycle but there is ownership. This represents “whole-part or a-part-of” relationship. This is represented by a hollow diamond followed by a line.
Let’s take an example of relationship between Department and Teacher. A Teacher may belongs to multiple departments. Hence Teacher is a part of multiple departments. But if we delete a Department, Teacher Object will not destroy.
It depends on the context.
Association: A man drives a car, focus on the caller and callee relationship.
Aggregation: A man has a car, focus on the owner and member relationship.
Composition: A man has a mouth, focus on the owner & member but the owner consists of members, it means that they shared the same life cycle.
Feels like I'm speaking Chinglish.
Association
Association is a relationship where all objects have their own life-cycle and there is no owner. Let’s take the example of Teacher and Student. Multiple students can associate with a single teacher and a single student can associate with multiple teachers but there is no ownership between the objects and both have their own life-cycle. Both can create and delete independently.
Aggregation
the objects in Aggregation have their own life-cycle but there is ownership. Child object can not belong to another parent object. Let’s take an example of Department and teacher. A single teacher can not belongs to multiple departments, but if we delete the department teacher object will not destroy. We can think about the “has-a” relationship.
Composition
It is a strong type of Aggregation. Child object does not have their life-cycle and if parent object deletes all child object will also be deleted. Let’s take again an example of the relationship between House and rooms. House can contain multiple rooms there is no independent life of room and any room can not belongs to two different houses if we delete the house room will automatically delete.
An association between object types classifies relationships between objects of those types. For instance, the association Committee-has-ClubMember-as-chair, which is visualized as a connection line in the class diagram shown below, may classify the relationships FinanceCommittee-has-PeterMiller-as-chair, RecruitmentCommittee-has-SusanSmith-as-chair and AdvisoryCommittee-has-SarahAnderson-as-chair, where the objects PeterMiller, SusanSmith and SarahAnderson are of type ClubMember, and the objects FinanceCommittee, RecruitmentCommittee and AdvisoryCommittee are of type Committee.
See also my alternative CodeProject article.