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?
Related
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.
I am trying to make a use case diagram with the help of my class diagram but the problem is i am here confused that what should i take as actors and what will come and what attributes shall i take and where to use <<extend>> ?
Kindly help. Thank you in advance.
As Thomas pointed out, there is no algorithmic way to go from a class design to a use case. In fact, for a given class diagram, it's not even granted that there is a use case at all (for example, if the classes represent only the relation between business objects and no actors).
However, by analyzing your specific diagram from a human point of view, you can very well infer a class diagram:
1) Identify candidate actors
An actor specifies a role played by a user or any other system that interacts with the subject. Candidates in your diagram are: visitor, admin, and registered user
The classes Movie, Book tickets, Make payment are obviously not representing roles of a user.
2) Identify candidate use cases
A use case defines the interactions of a system and an actor in order to achieve some goal. So let's brainstorm a little bit to find everything that looks like an interaction:
Very explicit candidate use cases: Book tickets (class and method of Registered user), Make payment (class and method of Registered user)
Less explicit candidate use cases or interactions: View movie (relation and method of Registered user), update movie (relation), Add movie record (method of admin), Update movie record (method of admin), delete movie record (method of admin), Confirm registration of visitor (inferred from relation), 'Get registered(method of a user),cancel ticket(and method ofRegistered user),Login(method ofRegistered user),Logout(method ofRegistered user),Update Seats available(method ofBook tickets), confirm transaction (method), refund money of cancelled ticket (method)
Implicit/inferred use cases or interactions : create and maintain admin , create a visitor, register and maintain a registered user account, anything else ?
3) Sort out the use cases
Among all the potential use cases and interaction identified, not all should get the use case status. You have then to find which are use cases and which are just interactions part of the same use case. For example:
update movie catalog would be composed of update movie, Add movie record, Update movie record, delete movie record.
Get registered and Confirm registration of visitor are obviously part of the same use case, because the goal is the same: registering a user.
...
I let you as an execise sort out the rest.
4) Review the actors
After having identified meaningful use cases you may want to review your candidate actors:
Some candidate actors might appear to be in fact only objects that are unrelated to users (it's not the case here, but it could be, for example, if you'd have a Movie producer, which is just an info related to a movie but not a user of the system).
Identify obviously missing actors for important use case that you have identified. Here for example, I first thought it was an internet movie business. But the method Update Seats makes obvious that we are talking of a real theater. So who would get the payment from the user, hand out the ticket, reimburse money in relation with the system ? If it's just the online booking system, we are fine. If the cahs desk operator shall use the system as well, then we should add this actor.
Find out relationship between candidate actors. A registered user was first a visitor. Shall we represent both of them in the diagram or not ?
5) Draw your use case diagram
Now you have all the elements, you can make your use case diagram. But you still have to decide on the level of detail you want to represent. Here a proposal:
You can not create a use case from a class design. Only the other way around. Form follows function, not vice versa.
Your class diagram indicates that you are not yet familiar with class modeling. Your classes Book Ticket and Make Payment sound like use cases rather than proper classes. A class is a container of data and functionality working on those data, whereas a use case is a piece of work that an actor performs with the help of the system.
Giving you the help you need might be too broad for this platform. Study introductory texts on UML modeling to get a feeling for what can be expressed by which type of model. And don't feel obliged to use all elements the language offers. There are plenty of use case models that don't need include and extend relations.
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.
I have this assignment for school where I have to model a sort of e-commerce site that delivers grocery bags to customers (http://www.linasmatkasse.se/). I haven't received any use case, or anything.
The only directions I've been given is that it's supposed to be a domain model of max 40 classes, of a web based business (like described above).
This is what I have so far.
Are the aggregations decent? (Especially between Customer and Account)
Should OrderStatus & AccountStatus be associated or not?
Is there any use for inheritance here?
Are there any redundancies, or anything that should be added?
Appreciate any feedback! Thanks!
change colors and font size of the picture, please - it is very hard to read.
Aggregations aren't OK. Composition - black diamond means, that item belongs to container and can't exist without it. Of course, an item can't belong to two containers this way. Change to shared one or two compositions. Customer and account CAN be connected so. But better think of Account as of association between Customer and Website.
Connect Cart and Order
Why OrderStatus and AccountStatus should be connected? I don't understand, why they need to be connected directly?
ItemDescription connect to item, or better, to ClassName, not itemlist
Why OrderItemList is connected to WebSite? What is it at all? Why Order is not enough?
What is SalesLineItem? Maybe, it should belond to OrderItemList?
Change ClassName to ItemClass - don't use terms accepted for other things.
Yes, you could use inheritance - Cart and Order should not be independent in this sense. But you'll decide, who is the parent. Or make "cart" one more status of Order. Or use both.
Heaps of things could be added, but obviously, it is not the real task, merely a piece of play. Think way of delivery, way of payment. Show navigability. Show names of arrows, not of connections.
Set attributes and functions.
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.