I'm beginning with UML and i'm trying to create a class diagram for a simple online shopping application. I would like to know if i should create an association beetween the following classes:
Card: A payment card
CardVerificator.
The responsability of the CardVerificator class is to check with the payment system if a card is valid or not. This class has one method with the following signature: verifyCard(Card):void (The method raises an exception when the given card is not valid).
(Sorry for my bad english)
Thank you.
You don't need an association here, only a dependency between those classes.
Association comes in the action, when you need a permanent, long-term link between the corresponding objects. In code is this situation often reflected through data members. Here we speak about a short-term limited contact that should even not be persisted (a simple method parameter instead of a data member).
CardVerificator should of course "know" the "Card" concept in order to be able to verify it, but this is nicely explained with a simple generic dependency:
Related
I have this basic class diagram:
and was wondering whether this object diagram is allowed:
The class diagram is given and I was wondering whether it is possible to create an object diagram where two customers (maybe wife and husband) are sharing the same bank account with this structure. But because a composition is used, the bank account would get deleted if one of the owners gets deleted right? So this class diagram is not really suitable for shared accounts, right?
This scenario for the objects in the second diagram is indeed not valid. The reason is that composition implies an exclusive ownership.
For an account to be shared by several customers you’d have to change the class diagram, for example:
use aggregation instead of composition (white diamond). Although its semantics are not well defined in the UML specification, it allows in any case for shared ownership.
use a simple association (without diamond). You could express the fact that an account has several customers with an explicit multiplicity.
use a composite client: the client could either be a single person, or a group of several clients. This construct is more complex.
Hi, I have recently started to learn system analysis and design and am having some trouble understanding domain model class diagram (DMCD) association class.
As per image, when drawing the DMCD, I'd like to understand if an association class is allowed to contain attributes of the classes it derives from. The Invoice needs to contain the attributes apptNo and svcName.
Association class inquiry image:
Do I include the attributes as shown in the image?
Or do I assume that the Invoice would already have these attributes because it is derived from Appointment and Service and that it is not necessary to include them as they can be referred back to the keys apptNo and svcID?
I am confused about the concept. How should I present the association class?
Can someone please provide some guidance?
Thank you.
As already pointed out by Geert Bellekens in his comment above, you don't repeat any of the attributes of the classes involved in an association class in the association class. You only include attributes that specifically characterize the links classified by the association class.
In your example, you should only include attributes that are specific for Invoice links, such as invNo, invDate and totalPrice.
This rule holds independently of the kind of class diagram (domain/design/implementation model).
However, your model is only good for invoices refering to one appointment and one service. It does not account for invoices concerning one appointment, no matter how many services it includes. In a model for this business logic, Invoice would no longer be an association class, but an ordinary class associated with Appointment. This would allow it to access each service included in an appointment and turn it into an invoice line.
To make it short:
is (sort of; please read the comments below) an alternative notation for
which means that Class3 already has associations to both Class1 and Class2. So there's no point in adding attributes of the latter in the association class. If you're on a DB level you eventually introduce redundancy for performance reason at the cost of violating the principle of single source of truth. But that's another story.
It depends.
A domain model class diagram models the concepts found in the domain, i.e. the part of the real world relevant for your project. In the classes, you only include attributes that are indicated by domain experts or by other sources describing the domain.
I will assume that a domain expert knows what an appointment number and a service name are. If these were just technical data, they should not be attributes of Appointment and Service in the first place. To determine whether these attributes should also be included in Invoice, you need to ask domain experts what they think. Does an invoice always include an appointment number and a service name? Only if the domain expert says "Yes", I would model them as attributes of Invoice.
(To double check, you could ask "Is it also valid to say that the appointment number is not part of the invoice, but that the invoice is somehow associated with an appointment having a particular appointment number?")
Maybe the domain expert says an invoice does not contain the appointment number or the service name, because the corresponding Appointment and Service are always associated to the Invoice as attachments or hyperlinks or otherwise. In that case, the fact that Invoice is an association class on the association between Appointment and Service is enough. You don't have to include attributes of these classes in Invoice. These will probably be added later, when the domain model class diagram is turned into a system model class diagram or database model class diagram.
I know this is an opinionated question. However it comes up often at work.
When creating methods it's often a struggle to know which class should be responsible.
e.g.
bool result = ProductService.CategoryHasSoldOutOfProducts(int categoryId)
vs
bool result = CategoryService.CategoryHasSoldOutOfProducts(int categoryId)
In my opinion, the CategoryService should be responsible, as the method is taking a categoryId and is specific to the Category.
Others at my work say the ProductService should be responsible as the method is dealing with if Products have sold out.
Just trying to develop a better understanding of service architecture and good process. I'm interested in other peoples explanations for why they would choose one over the other.
Thanks
Disclaimer - this is a purely IMHO answer. I am answering this in the spirit of having a design brainstorm.
Based on the OP, it seems the relationship between Category and Product is an optional one to many : Category (0..1) <--------> (*) Product.
Implementation wise, this means that the Category entity probably has a Container of Products, and the Product entity has a reference to a Category which may be NULL.
In this case, I agree with the decision to place CategoryHasSoldOutOfProducts under the responsibility of the Category entity. The method name clearly implies that the Category entity should be responsible for informing its API user on the status of its products.
There is another option, however: An association class/entity. The motivation behind this entity is to describe the relationship between two other entities.
In this case, you can have a functional association entity which we will call ProductContainment for the sake of this example.
ProductContainment will have no internal state, and will hold functions which are provided with Category and/or Product entities as parameters.
It is then the responsibility of the association entity to provide the implementation of functions which relate to how Category and Product relate to one another.
If you end up using ProductContainment - then CategoryHasSoldOutOfProducts should be one of its functions.
Since you're asking for opinions, here is mine:
(Disclaimer: That's probably something you cannot easily implement in the business world)
As you are using the term "class", I assume you want to have something object-oriented. The problem is, a service is nothing a valid object could be created from. Instead, it's just a namespace for functions.
Additionally it's very general. It's like calling a class "Manager". You can put possibly everything inside of it and this class has the potential to grow to have hundreds of functions.
My advice: Create small entities. Small enough to be created without the use of any setters, just by calling the constructor. If you notice your object needs more functionalities, create a decorator that is a little bit smarter and can do the work for you.
I would need a few more details about your environment to be more precise, but I guess in your case, you would have something like a Category class that contains products and knows when it's sold out. Just imagine you have a team of persons and everyone knows something. Ask the right guys to do the stuff and stay away from managers or services.
The diagram below is based on these facts:
A citizen may make a claim / reclamation on pollutions
An administrator will send the reclamation by type to the appropriate agency / organization, and it will respond with a diagnostic report
This report will be sent by the administrator, to another organization, for the estimation of the solution (costs, etc.).
My problem is to how can I show that Admin will send the claim to an agency? Do I have to make an association between Organization and Reclamation?
If your requirements include that the communication between the Admin and the Organization is to be documented, then you need to take care of this in your class diagram. And, in fact, you already have an item for this: the NotifyOrganization association class. Notice, however, that it's not a good idea to use the questionable UML concept of an association class, which does not have a clear semantics and is confusing. This seems to be confirmed by your flawed modeling of the multiplicities of the NotifyOrganization association, which must not be one-to-one (or 1 to 0..1), but rather many-to-many (* to *).
So, better replace the NotifyOrganization association class with an ordinary class (possibly with an improved name such as Notification) and attach it to Admin and Organization with two many-to-one associations such that each notification is linked to exactly one admin and one Organization.
Notice that a notification represents a (communication/message) event, so Notification represents an event type. It*s quite common in business information models to have both object types and event types, both as classes in a UML class diagram.
...how can I show that Admin will send the claim to an agency?
UML Class Diagram is not show-everything document. In order to document that admin will send claim to agency you can document it effectively using UML Sequence Diagram or some other behavior diagram
...do I have to make an association between Organization and Reclamation?
No, if the agency does not need to care about who exactly delivered the claim or what's the person's role (e.g. "admin"), then you don' have to add it to the class model (and show some association) at all
...diagram...based on these facts...
In order to describe the overall process in a one-page style picture, you (and your business partners) can find very useful the Business Process Model and Notation (BPMN) graphical language in addition to UML
Why and how are dependency relationships used?
I've come across a PiggyBank example where the Analysis Model consists of a class diagram with dependency relationships.
They use two relationships "use" and "instantiate" to describe the relationships between the classes.
I don't agree with the relationship that the boundary class TransferMoneyForm has a "use" to the TranferMoneControl. I believe it should be the other way around.
Can someone exaplain to me how these two relationships should be used. Thank you in advance.
The diagram shown there is not a correct and full UML class diagram. In such all the associations and generalizations should be defined, and what is abstract, what is public or not. To show what descends from what, what is hidden, what will be never instantiated and what fields of one class has types of other classes. Here we see only information about the
functions.
And it is logical. If you'll look at the previous chapter, there is written: "A control class represents a self-contained process..." So, they are talking on processes, not classes, instances and fields.
It is NOT a class diagram. And nowhere is said that it is. It is named "Transfer Money Participants diagram". They do use the elements of the class diagram, but not to the fullest and so create something more common. It is some approximate undefined diagram on some classes, something between class, communication or component diagrams. Maybe, it is the old style of IBM? Experts (What's the best UML diagramming tool?, 1st answer) say, "IBM Rational Software Architect did not implement UML 2.0". )
As for the question, who uses whom... According to Sparx VP UML, a "usage dependency" is a "relationship in which one element requires another element ... for its full functionality". According to wiki, "The client element somehow "uses" the supplier". Here the form hasn't sense without the controlling class, and vice versa. So, I'd say, the use goes in both sides. But more honest would be to create a normal communication or component diagram. The class diagram has NOT an element to say about sending and accepting the messages. And the "use" is definitely not for it. And when they have decided not to use logic, they can put there virtually anything.
If you are making a class diagram and one your class uses function(s) of another one, that is the case to draw a use dependency connection.