I am working on an online web store. It's a simple web store and I have to create domain UML diagrams for the class and show multiplicities. I am kind of confused about the multiplicity that I have came up with. I don't know how to distinguish between composition, aggregation and association. Below is the diagram that I have came up with. Can someone tell me if I am on the right track?
http://i.imgur.com/8FwhsaI.jpg
Not too bad. You should not bother to much with aggregation unless you need to deal with memory management or foreign key constraints in database design. Just leave them away.
One important change you should make are the role names for associations. E.g. instead of shippingAddress:Address declared as attribute use a role shippingAddress appearing near association on Address that comes from User (etc. for the other ones).
Since Address is sort of a common-place and used all over, you could leave the class out of this diagram and make a separate diagram where Address is in the middle and all others using it surround it.
I agree with Thomas, but I will show other points so can you adjust your diagram.
Please don't see as something destructive. I just believe these tips can help you.
show multiplicities of every connection
do not use getter and setter *
do not use ID's attributes *
Order makes composition with User (does not make sense have an order with a user related with it and OrderLine makes composition with Order;
Product make aggregation with OrderLine and Review make composition with Product;
Manufacturer makes aggregation with Product. ( depend on your system, it can be a composition, but it more likely to be an aggregation).
Remember (the part) makes something with (the whole)
it does not need to create an attribute in a class if you have a connection with that class, except when you have a list of it,( e.g.1: attribute CreditPayment in Payment and Class CreditPayment );
You could make a List of Product in Order. After this, you could delete the Orderline Class.
*if you will not generate a code from the model.
Related
We're tasked to make a system that will record students daily in and out of the institution premises via student ID, to ensure student safety, and The instructor can also use this system as the student attendance.
Can you help me by checking if this is correct or any improvement is required?
In short
There are some syntactic issues with the associations in your diagram.
Moreover, associations correspond to a structural relationship. Do not create associations, simply because one class uses another at some point in time: for a simple use, a «use» dependency is the most you can do.
More details
Syntactically, this diagram seems correct, except for the label on the association:
Since it's in the middle of the line, we assume it's the association name. But the association name has no visibility.
Since there is a - (private) visibility, we understand that it could be the role of an association end. But It should then be located on the end and not in the middle.
Semantically, from an UML point of view there are some suspicious relationships:
The double composition of Login is probably wrong: composition indicates an exclusive ownership. Your diagram says that a Login occurence is owned either by an Admin or by a Teacher but if it's owned by one, the other cannot be related to it.
Moreover, composition suggest a part-whole relationship and I don't see a login to "be a part of" a teacher or an admin.
The aggregation is not well defined in UML and therfore does not really add value. Some people see it suggesting a part§whole relation with non-exclusive ownership: in this case it would be wrong. Better get rid of it.
The name of the Validates association is confusing as it corresponds to a Login's operation. It might lead to think that the line corresponds to the dynamic invocation of the operation, whereas in reality an association is structural.
But it's difficult to say more in absence of any requirement or analysis context. Based on my domain knowledge:
The 1 to 1 association between Admin and Student must be wrong, since an Admin may enrol 0 users (new admin), or many users
There's a login which is probably used to monitor the in's of the students, but nothing seems to monitor the outs.
Do each student have only one single teacher ?
It's not clear to me if all these associations are a structural relation. For example, we can understand that at a point in time, in a transaction, a teacher validates a login. But should a trace of this validation be kept (i.e. do you expect to be able to later find out all the logins that a teacher has validated? or to find for a given login which teacher did validate it?).
I've never made a class diagram before, that's why I tried to ask. I always learn from my mistake. I have read some references, but I am confused how to test the results I made? because this is not a coding which if have error, the error message will be appear.
this my design database
and this is a class diagram that I made based on design database.
is the method for creating class diagrams similar to erd? I am very confused how to inherit the class and which arrow should I use?
in the path that I made there are three users. and each has a different role
Public Relations = Input data from external user (the applicant comes and gives a written proposal) then the data is stored in the database. The data includes applicant data and proposal data. PR can also see data that has been confirmed by the Division
Division = The division can see data that has been stored by PR and confirm the data. Data that has been confirmed will be filed and made a report.
Manager = can only see reports
Here are a couple of findings:
User->Login: This is no generalization. A user isn't a login. It might have some login information associated. So that shall be an association.
Similar for Proposal->StatusProposal. But here it's a dependency since you will not create an enumeration object. You just use it to type an attribute.
Same for User->Gender/RoleUser. Both are dependencies.
There are also a couple of design issues. But here YMMV too much. Having User implement userLogin() is at least questionable. There should be a security system taking care which validates a user login. So why does Login have a loginStatus()? However, design is not be discussed here.
As to class/ERD: they are similar, but not the same. UML has a broader scope while ERD focuses plainly on databases. So all the *_id attributes in your classes stem from a database design. The class design in that state is very much focused on databases. In a MDA it might be derived from a PIM to a PSM (so from an abstract view to a DB-specific one).
In addition to Thomas Killian's observations, your composition associations appear to be inaccurate. In effect, for example, you are specifying that the lifetime of a Department object is dependent on the lifetime of a User object. You are also specifying a whole-part relationship between Users and Departments, where the user is an aggregation of departments. I would think that it's the other way around. I also suspect that a user's lifetime isn't dependent on a department's lifetime, since a user can typically change departments. Therefore, an aggregation diamond (white) is probably correct, and it should be on the Department end.
Similarly, I have trouble making sense of your other two composition associations.
First, don't think i'm trying to get the job done by someone else, but i'm trying to design a class diagram for a domain model and something I do is probably wrong because I'm stuck, so I just want to get hints about what i'm not doing correctly to continue...
For example, the user needs to search products by categories from a product list. Each category may have subcategories which may have subcategories, etc.
The first diagram I made was this (simplified):
The user also needs to get a tree list of categories which have at least one product.
For example, if this is all the categories tree:
Music instruments
Wind
String
Guitars
Violins
Percussion
Books
Comics
Fiction
Romance
I can't return a tree of Category which have at least one product because I would also get all subCategories, but not each sub category has a product associated to it.
I also can't remove items from the Category.subCategories collection to keep only items which have associated products because it would alter the Category entity, which may be shared elsewhere, this is not what I want.
I thought of doing a copy, but than I would get 2 different instances of the same entity in the same context, isn't it a bad thing ?
So I redesigned to this:
Now I don't get a collection of child categories I don't want with each Category, I only know about its parent category, which is ok.
However, this creates a tree of categories which is navigable only from the bottom to the top, it makes no sense for the client of ProductList who will always need a top -> bottom navigation of categories.
As a solution I think of the diagram below, but i'm not sure it is very good because it kinda dupplicates things, also the CategoryTreeItem does not seems very meaningful in the domain language.
What am I doing wrong ?
This is rather an algorithmic question than a model question. Your first approach is totally ok, unless you were silent about constraints. So you can assign a category or a sub-category to any product. If you assign a sub-category, this means as per this model, the product will also have the parent category. To make it clear I would attach a constraint that tells that a product needs to be assigned to the most finest know category grain. E.g. the guitar products would be assigned to the Guitar category. As more strange instrument like the Stick would get the Strings category (which not would mean its a guitar and a violin but just in the higher category.
Now when you will implement Category you might think of a method to return a collection of assignedInstruments() which for Guitar would return Fender, Alhambra, etc. You might augment this assignedInstruments(levelUp:BOOL) to get also those instruments of the category above.
Generally you must be clear about what the category assignment basically means. If you change the assignment the product will end up in another list.
It depends on the purpose of the diagram. Do you apply a certain software development method that defines the purpose of this diagram in a certain context and the intended readers audience?
Because you talk about a 'domain model', I guess your goal is to provide a kind of conceptual model, i.e. a model of the concepts needed to communicate the application's functionality to end users, testers etc. In that case, the first and the second diagram are both valid, but without the operations (FilterByCategory and GetCategories), because these are not relevant for that audience. The fact that the GUI only displays a subset of the full category tree is usually not expressed in a UML diagram, but in plain text.
On the other hand, if your intention is to provide a technical design for developers, then the third diagram is valid. The developers probably need a class to persist categories in the database ('Category') and a separate class to supply categories to the GUI ('CategoryTreeItem'). You are right that this distinction is not meaningful in the domain language, but in a technical design, it is common to have such additional classes. Please check with the developers if your model is compatible with the programming language and libraries/frameworks they use.
One final remark:
In the first diagram, you specified multiplicity=1 on the parent side. This would mean that every Category has a parent, which is obviously not true. The second diagram has the correct multiplicity: 0..1. The third diagram has an incorrect multiplicity=1 on the composition of CategoryTreeItem.
From my perspective your design is overly complex.
Crafting a domain model around querying needs is usually the wrong approach. Domain models are most useful to express domain behaviors. In other words, to process commands and protect invariants within the correct boundaries.
If your Product Aggregate Root (AR) references a Category AR by id and this relationship is stored in a relationnal DB then you can easily fulfill any of the mentionned querying use cases with a simple DB query. You'd start by gathering a flat representation of the tree which could then be used to construct an in-memory tree.
These queries could be exposed through a ProductQueryService that is part of the application layer, not the domain as those aren't used to enforce domain rules or invariants: I assumed they are used to fullfil reporting or UI display needs. It is there you could have a concept such as ProductCategoryTreeItemDTO for the in-memory representation.
You are also using the wrong terms according to DDD tactical patterns in your diagrams which is very misleading. An AR is an Entity, but an Entity is not necessarily an AR. The Entity term is mostly used to refer to a concept that is uniquely identified within the boundary of it's AR only, but not globally.
So I'm working on an assignment for school, where I am to model (using a domain model) a web shop that delivers complete grocery bags to people's homes. (http://www.linasmatkasse.se). I wish I could be more specific here, but this is all I have unfortunately.
I haven't received any use case, but the scenario would be something like, add bag to cart, create account/add info, pay.
This is what I have so far : http://i.imgur.com/BIljBtj.png?1
Are there any redundancies? (I only have to depict the model of the site, unsure how much to include).
Could/Should I add composition between for instance Customer and Account, Cart and OrderLineItem, Order and Cart?
Pretty uncertain about attributes & multiplicites in general. Any feedback or support here is appreciated.
Payment class? Is it needed? Should it have payment methods included?
Should I model human elements like support?
Should I model more of the delivery
Is association between customer and order needed?
Thanks a bunch! Again...
It should be a class diagram. So, such verbs as "has", "contains", should be shown as aggregation, "supplies", "describes", "makes" should appear on associations arrows only if these names are the names of the attribute in the source(for arrow) class. "owns" should be shown as a dot on the end of association. Also put attribute names really on ends of the associations. You can name the whole associations, but that implies, that the association itself, without the instances of the classes, somehow exists. If you want to write comments, they are to be placed on the notes. But normally that words as "supplies", "describes", "makes", "has", "contains", "owns", appear on the Use case diagram. Make it apart from the class diagram, if you want to think on this logic or discuss it with a client or a sales manager you work with.
Composition
That one between Account and Cart you have made very nicely. Thus you cay, that Cart doesn't exist out of its Account and any account has only one cart. So, the composition with multiplicity 1 to 1 is sensible and bears a lot of important info.
The customer as you made it, is useless. You need only Account.
Till now I don't understand the use of OrderLineItem and ItemList. If the use of some classes is not obvious, it is bad - at least put comments there or think, if you really need them.
Payment - yes, it is necessary. As for payment methods, put them in the specific Enumeration class block, name them there as items and connect Payment to PaymentMethods.
No human elements here! You are deep into the IT model, on the border of coding. You really want to do a use case diagram, don't you?
Delivery? Maybe more enumerations for way of delivery and supplier, ClientAddress that is seen from Account, Order. It is for you to decide if you want to cover this or that scope.
ItemDescription should be connected to Item only
All you associations are navigable in both ways. It is senseless. Choose the navigability.
If a class attribute is an instance of another class, put a dot on that another end of association (end owned by classifier).
Supplier connected to Order? Do you want to cover the theme of trade with suppliers, too? Then there should be more classes on that theme. And it could be another component and another class diagram. Or is there a graphic error?
I am creating a Class Diagram for a simple booking system for the theater. I would like to know if the diagram makes any sense and if anything needs to be changed (arrow directions) in order for it to be correct?
Thanks.
Image URL: http://i.stack.imgur.com/zWiGW.jpg
Here are some recommendations that you're free to incorporate or ignore as you see fit:
I don't agree with the relationship between Show and Venue. It seems more natural to have a Booking maintain the relationship between a Show and a Venue.
I don't see a Date for a Show anywhere. Did I miss it? That seems important.
Shows don't have Seats; a Venue has Seats.
A Ticket ought to entitle you to a Seat in a Venue on a particular date. I don't see that.
TicketType should be nothing but an enum.
Decompose User to have a Name, Address, and Credential classes. Separate the Credentials out from User.
A real payment system would need far more than what you have showing (e.g. CreditCard, etc.)
I think your model needs a lot of work.
In addition to what duffymo said, here are some generic observations not strictly related to this particular diagram but rather you modeling practices.
If an association is one way navigable then there is no need to name both ends. You have named both ends of all associations, but only navigable end needs a name.
Drop the 'can' from all association ends. In some cases there is a handy term, for example show can be hosted at a Venue. But in other cases it's perfectly fine and even common practice to name association ends same as the class at that end. (so name the Seat end simply Seats)
Avoid many to many relationships if you can. If you can't then look into adding an association class in between, it almost always makes sense.