Should I put the test classes in the UML diagram? I can't find any "best practice" about this!
It depends. Firstly "the UML diagram" suggests that you are creating a single diagram. This is definitely not good practice. Create as many diagrams as needed lighting certain aspects of the model. So - test cases would be one of those aspects. That means: put them in (a) separate diagram(s).
To add a suggestion, if you want to model tests, you can look to UML testing profile ( UTP link) it provides needed elements to model tests, requirements and so on.
You can use SysML also since it integrates a part of UTP.
It definitely depends on context. Who is going to use the UML model and what will they use it for? In general I would say that adding test classes is going to clutter a UML model and make it difficult to understand - so no. But if the context is that the testing is what you want to explain, then clearly the test classes are going to be pretty important.
As Thomas Kilian points out, creating a number of diagrams from one underlying model is probably the right answer - and being able to do this is one of the reasons you would use UML rather than a simple diagram.
This is a preference. You can choose to or choose not to.
I would say it's better practice to have the tests modeled into the solution. But I wouldn't claim I always follow best practices 🙊
There are many diagrams needed in modeling a solution. I would focus on three: Analysis, Design, and Implementation. All three are class diagrams. All three define your solution at different abstractions.
In the analysis, you're closest to the requirements and the beginning of your solution. In here, you would want to have broad classes. I would not put tests in here since this diagram is still trying to get the shape of the solution from the user and their requirements. An analysis diagram would only have class names in a box, with lines which show their associations.
The design diagram would go into a little more detail on how classes would be built. The blueprint of the application would take shape in the design. This design can be given to any programmer and they write code which would build the solution. The interesting part of the design diagram is that it could also be given to a test engineer and they would write proper tests for the solution to be created.
The implementation diagram is the lowest level class diagram which is created. Most times, I would create this in retrospect. The implementation diagram should be a verbatim translation of the codebase. In the implementation diagram, I would have my test classes included for completeness.
Note, these are my views which I sometimes do not follow to the letter because of business constraints. However, in an ideal world, this is how I would prefer my modeling done.
Related
I am beginning in UML and software analyse and i do not understand how UML and diagrams can influence coding and software architecture while we can directly build the code and its data base without diagrams.
I read lot of tutorials abouat the subject but not enough to understand the utility of UML in coding.
I understand everey diagram and its role. That is not my problem but i do not yet understand their roles after the analyse and design phase.
So what is the role of UML in coding phase of a software ?
Thank you.
The comment by #xmojmr already puts it right. UML creates a model (hence the M in UML) of a system. A model reduces information of a system to a level so it is a) manageable and b) complete. Human brains are not computers and you need a means of communication what the system is all about. You can do that as pure code, as paper document and as UML model. A combination of all is not uncommon. As long as you have tiny systems you can live with pur code and tools like Doxygen. But once it starts getting complex you need some handles. UML offers these to end users, architects, testers, developers, managers, etc. Along with UML you will also need a methodology. UML delivers the syntax how to document a system. But you need some structure above to write a nice novel.
UML-based models play an essential role for coding/implementing a software system in model-based (or model-driven) development. The basic idea is that you start making a model of your problem domain (the domain model), then you derive from it a platform-independent design model, which can be transformed into platform-specific implementation models (e.g. for Java- or C#-based platforms) that are finally encoded in the target languages.
The most prominent part of model-based development is the encoding of model classes (forming the model layer in an MVC architecture for apps) based on a data model (a UML class model) that has been derived from an information design model, which was obtained from a domain information model (where all these information/data models are UML class models).
You can find an instructive example of model-based development in my tutorial book Engineering Front-End Web Apps with Plain JavaScript.
This one is in my point of view a duplicate of that other question. It can't be flagged because there is no accepted answer. The related question on meta stackexchange does not provide a clear solution to that situation.
I think my personal answer was relevant and is applicable to the current question.
To be synthetic, Martin Fowler considers current uses of UML. I think he describe the current practices. Perhaps should these evolve ?
Perhaps would the initial question be the right place to discuss ?
Much has been written about testing of code. But how do we ensure that our design is functionally correct in the first place? Just as we have JUnit for testing Java code, are there some tools that can be used, say, to test a UML based design, where the tests are expressed in form of functional requirements?
These are some vague thoughts, but wanted to know if there's a methodical, automatable approach to testing the design first. In other words, can we also have 'Test Driven Design'?
are there some tools that can be used to test a UML based design, where the tests are expressed in form of functional requirements?
You cannot test a design based on functional requirements because the satisfaction of functional requirements depends on the implementation, not on the design.
In other words, you can follow a bad design (any one of the infinite possible designs) and still meet that set of functional requirements if you implement the required behavior.
Interesting topic!
Firstly, no software architects in my personal network use UML as the only way to design their systems, and I also know of no software architects who create UML at the level of detail required to execute a mechanical test.
Secondly, I personally have a deep dislike of the UML modeling tools. If such a formal verification method is implemented, it's likely to be in something like Rational Rose - I swore long ago I'd never go anywhere near that again.
However, having said all that - in formal software shops, it's common to have requirements tracability, typically implemented as a matrix which shows business requirements on one axis, and design artifacts on the other. This way, you can see whether any requirements are not matched with a corresponding solution, or if there are elements in the solution which do not meet a specific business requirement.
Keeping this matrix updated is a pain, so it's not often used in agile teams, but if you're building softwware for a bank or the space shuttle, it is a valuable technique.
This tells you whether your design is complete - though not whether it's "right".
There's no way I know of to tell whether a design is "right" without either building it and testing, or relying on human experience and knowledge.
Let's say I've made a list of concepts I'll use to draw my Domain Model. Furthermore, I have a couple of Use Cases from which I did a couple of System Sequence Diagrams.
When drawing the Domain Model, I never know where to start from:
Designing the model as I believe the system to be. This is, if I am modelling a the human body, I start by adding the class concepts of Heart, Brain, Bowels, Stomach, Eyes, Head, etc.
Start by designing what the Use Cases need to get done. This is, if I have a Use Case which is about making the human body swallow something, I'd first draw the class concepts for Mouth, Throat, Stomatch, Bowels, etc.
The order in which I do things is irrelevant? I'd say probably it'd be best to try to design from the Use Case concepts, as they are generally what you want to work with, not other kind of concepts that although help describe the whole system well, much of the time might not even be needed for the current project. Is there any other approach that I am not taking in consideration here? How do you usually approach this?
Thanks
Whether DDD, or not, I would recommend with determining the ubiquitous language (UL) by interviewing the product owner(s). Establishing communication in a way that will have you and the product owners speaking the same language not only aides in communication, but being able to discuss the project in common terms tends to help the domain model define itself.
So, my answer is basically to discuss, listen, and learn. Software serves a need. Understanding the model from the viewpoint of the experts will lay the solid groundwork for the application.
I'd start by a drawing a class diagram with all the relationships and implement only the classes that are necessary according to the requirements of your application.
You can use an anemic approach (attributes plus getters and setters) to keep things simple and avoid the step of writing business logic in the same step. With an anemic model, the logic would go into a corresponding Service class. That way you can consider Use Cases later on.
I know some people don't appreciate this way of doing things but it does help with maintenance and avoids some dependency issues.
Answer to devoured elysium's question below:
In terms of analysis, starting with Use cases (What) and then proceeding to the class diagram (How) sounds like a good rule of thumb. Personally, I'd do the Sequence diagram (When and Who?) afterwards, as you'd need to know between which processes/objects messages need to be sent.
Beyond that my take on things is that UML is simply a way to model a system/project and not a methodology by itself (unlike Merise, RAD, RUP, Scrum, etc.). There is nothing stopping someone starting off with any diagram as long as they have the sufficient information to complete it. In fact, they should be done simultaneously since each of the diagrams is a different perspective of the same system/project.
So, all in all it depends on how you go about the analysis. During my studies I was taught the rigid waterfall approach, where you do a complete analysis from start to finish before producing some code. However, things can be different in practice, as the imperative might be to produce a working application in the least time possible.
For example, I was introduced to the Scrum methodology recently for an exercise involving the creation of a web site where people can post their fictions. As there was a time constraint and a clear vision of what should be achieved, we started right away with a bare bones class diagram to represent the domain model. The Use cases were then deduced from a series of mock screens we'd produced.
From memory, the classes were Story, Chapter, User and Category. This last class was phased out in favour of a more flexible Tag class. As you'd imagine, the complete class diagram of the existing project would be much more complex due to applying domain driven design and the specificities of the Java programming language.
This approach could be viewed as sloppy. However, a web site like this could easily be made in a couple of weeks using an iterative process and still be well designed. The advantage an iterative process has over the waterfall approach is that you can continually adjust requirements as you go. Frequent requirements changing is a reality, as people will often change their minds and the possibility of producing a working application after each iteration allows one to stay on course so to speak.
Of course, when you're presenting a project to a client, a complete analysis with UML diagrams and some mock screens would be preferable so they have an idea of what you're offering. This is where the UML comes in. Once you've explained some of the visual conventions, an individual should be able to understand the diagrams.
To finish off, if you're in the situation where you're trying to determine what a client wants, it's probably a good idea to gradually build up a questionnaire you can bring with you. Interviewing a person is the only way you can determine what concepts/features are really needed for an application, and you should expect to go back in order to clarify certain aspects. Another tip would be to do some quick research on the web when you're confronted with a subject matter you're unfamiliar with.
In your example, this would be to go through the basics of anatomy. Among other things, this will help you decide what the model should contain and what granularity it should have (What group of organs should be considered? How precise does it need to be? Do only the organs need to modeled or should they be decomposed into their constituents like tissues, cells, chemical composition, etc. ?).
I think the place to start would be whatever feels logical and comfortable. It's probably best to start with the use cases, as they give you clear direction and goals, and help you avoid YAGNI situations. Given that you should be trying to develop a strong domain model, it shouldn't really matter, as the whole picture of the domain is important.
I would like to share my experience for such type of situations. I usually start with writing tests and code. And try to cover one end to end use case. This gives me fair enough idea about problem and at the end I also have something working with me which I can show case to my client. Most of the time subsequent stories build on top of previous one, but it also happens to me that subsequent stories require changes in the previous model I came up with. But this does not impact me as I already have good test coverage. In this way I came up with the model which fits for the current problem, not the model which maps the real world.
You start with Business Requirements which can be formalized or not. If formalized you would use Use Case Diagrams.
For example here are use case diagrams for an e-commerce app:
http://askuml.com/blog/e-commerce/
http://askuml.com/files/2010/07/e-commerce-use-case.jpg
http://askuml.com/files/2010/07/e-commerce-use-case2b.jpg
From these use cases, you can naturally deduce the business entities: product, category of product, shopping cart, ... that is start to prepare class diagrams.
This is best practice in many methodologies but this is also just common sense and natural.
Short answer
Pick a use case, draw some collaboration diagram (and a class diagram) to realize the domain objects involved. Concentrate only on those objects participated in order to accomplish use case goal. Write TDD test case to set the expectation and gradually model your domain classes to meet the expectations. TDD is very helpful to understand the expected behaviors and it helps to get the cleaner domain model. You will see your domain evolve gradually along with the TDD expectations.
Long answer
My personal experience with DDD was not easy. That was because we didn't have necessary foundations in the first place. Our team had many weak points in different areas; requirements were not captured properly and we only had a customer representative who was not really helpful (not involved). We didn't have a proper release plan and developers had a lack of Object Oriented concepts, best principles and so on. The major problem we had was spending so much time on trying to understand the domain logic. We sketched many class diagrams and we never got the domain model right, so we stopped doing that and found out what went wrong. The problem was that we tried too hard to understand the domain logic and instead of communicating we made assumptions on the requirements. We decided to change our approach, we applied TDD, we started writing the expected behavior and coded the domain model to meet the TDD's expectations. Sometimes we got stuck writing TDD test cases because we didn't understand the domain. We straight away talked to the customer representative and tried to get more input. We changed our release strategy; applied agile methodology and release frequently so that we got real feedback from the end user. However, needed to ensure the end user expectation was set at the right level. We refactored based on the feedback, and in that way the domain model evolved gradually. Subsequently, we applied design patterns to improve reusability and maintainability. My point here is that DDD alone cannot survive, we have to build the ecosystem that embraces the domain, developers must have strong OOP concepts and must appreciate TDD and unit test. I would say DDD sits on top of all the OOP techniques and practices.
Just I am new to Object Modelling.I want to know still there is a need to use Sequence Diagram, Use case Diagram to develop an object model or any other new technology is available?
Update :
CRC (Class,Responsibilites,Collaborator) is very limited ?
It depends on the team or teams you're working with. The chief benefit of UML is that you can share diagrams with other individuals and teams without having to learn each others diagramming language. If the team you're working with doesn't know UML, it may not be worth going down that road unless everyone is interested and you know you'll be working together for a while.
In my experience UML sequence diagrams and object model diagrams are very usefully and generally understood by all. Sequence diagrams in particular have the ability to resolve design issues through the disipline of their construction. I haven't found use case diagrams to be as useful. Requirements are challenging and strongly dependent on human and organizational factors regardless of the methodology.
If you're communcating with non-technical stakeholders, UML is a waste of time because they won't have studied it. Use simple, well annotated diagrams. Colors are very effective.
If your team is all onsite, sometimes there's nothing better than a couple of whiteboards and a freeform diagramming style.
You don't necessarily need these items. They are just aids which are available if you choose to utilise them. They are particularly useful in a business environment where you need to articulate your architecture to fellow developers, but you can choose to use whatever you like, inc. your own personal standards or no standards at all!
"any other new technology is available?"
No.
UML pretty much dominates. A classic ERD is just a specialized class diagram that omits the method box from each class. Also, classic ERD's use crows feet instead of text annotation for cardinality and optionality. So ERD's are actually part of UML.
You can read about OPM, if you want something slightly different. They appear to combine an activity diagram and a class diagram into one thing: a process-data diagram.
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I recently read an interesting comment on an OOP related question in which one user objected to creating a "Manager" class:
Please remove the word manager
from your vocabulary when talking
about class names. The name of the
class should be descriptive of its'
purpose. Manager is just another word
for dumping ground. Any
functionality will fit there. The word
has been the cause of many extremely
bad designs
This comment embodies my struggle to become a good object-oriented developer. I have been doing procedural code for a long time at an organization with only procedural coders. It seems like the main strategy behind the relatively little OO code we produce is to break the problem down into classes that are easily identifiable as discrete units and then put the left over/generalized bits in a "Manager" class.
How can I break my procedural habits (like the Manager class)? Most OO articles/books, etc. use examples of problems that are inherently easy to transform into object groups (e.g., Vehicle -> Car) and thus do not provide much guidance for breaking down more complex systems.
First of all, I'd stop acting like procedural code is wrong. It's the right tool for some jobs. OO is also the right tool for some jobs. So is functional. Each paradigm is just a different point of view of computation, and exists because it's convenient for certain problems, not because it's the only right way to program. In principle, all three paradigms are mathematically equivalent, so use whichever one best maps to the problem domain. IMHO, if using a multiparadigm language it's even ok to blend paradigms within a module if different subproblems are best modeled by different worldviews.
Secondly, I'd read up on design patterns. It's hard to understand OO without some examples of the real-world problems it's good for solving. Head First Design Patterns is a good read, as it answers a lot of the "why" of OO.
Becoming good at OO takes years of practice and study of good OO code, ideally with a mentor. Remember that OO is just one means to an end. That being said, here are some general guidelines that work for me:
Favor composition over inheritance. Read and re-read the first chapter of the GoF book.
Obey the Law of Demeter ("tell, don't ask")
Try to use inheritance only to achieve polymorphism. When you extend one class from another, do so with the idea that you'll be invoking the behavior of that class through a reference to the base class. ALL the public methods of the base class should make sense for the subclass.
Don't get hung up on modeling. Build a working prototype to inform your design.
Embrace refactoring. Read the first few chapters of Fowler's book.
The single responsibility principle helps me break objects into manageable classes that make sense.
Each object should do one thing, and do it well without exposing how it works internally to other objects that need to use it.
A 'manager' class will often:
Interogate something's state
Make a decision based on that state
As an antidote or contrast to that, Object-Oriented design would encourage you to design class APIs where you "tell don't ask" the class itself to do things itself (and to encapsulate its own state): for more about "tell don't ask" see e.g. here and here (and maybe someone else has a better explanation of "tell don't ask" but these are first two articles that Google found for me).
It seems like the main strategy the little OO code we produce is to break the problem down into classes that are easily identifiable as discrete units and then put the left over/generalized bits in a "Manager" class.
That may well be true even at the best of times. Coplien talked about this towards the end of his Advanced C++: Programming Styles and Idioms book: he said that in a system, you tend to have:
Self-contained objects
And, "transactions", which act on other objects
Take, for example, an airplane (and I'm sorry for giving you another vehicular example; I'm paraphrasing him):
The 'objects' might include the ailerons, the rudder, and the thrust
The 'manager' or autpilot would implement various commands or transactions
For example, the "turn right" transaction includes:
flaps.right.up()
flaps.left.down()
rudder.right()
thrust.increase()
So I think it's true that you have transactions, which cut across or use the various relatively-passive 'objects'; in an application, for example, the "whatever" user-command will end up being implemented by (and therefore, invoking) various objects from every layer (e.g. the UI, the middle layer, and the DB layer).
So I think it's true that to a certain extent you will have 'bits left over'; it's a matter of degree though: perhaps you ought to want as much of the code as possible to be self-contained, and encapsulating, and everything ... and the bits left over, which use (or depend on) everything else, should be given/using an API which hides as much as possible and which does as much as possible, and which therefore takes as much responsibility (implementation details) as possible away from the so-called manager.
Unfortunately I've only read of this concept in that one book (Advanced C++) and can't link you to something online for a clearer explanation than this paraphrase of mine.
Reading and then practicing OO principles is what works for me. Head First Object-Oriented Analysis & Design works you through examples to make a solution that is OO and then ways to make the solution better.
You can learn good object-oriented design principles by studying design patterns. Code Complete 2 is a good book to read on the topic. Naturally, the best way to ingrain good programming principles into your mind is to practice them constantly by applying them to your own coding projects.
How can I break my procedural habits (like the Manager class)?
Make a class for what the manager is managing (for example, if you have a ConnectionManager class, make a class for a Connection). Move everything into that class.
The reason "manager" is a poor name in OOP is that one of the core ideas in OOP is that objects should manage themselves.
Don't be afraid to make small classes. Coming from a procedural background, you may think it isn't worth the effort to make a class unless it's a thousand lines of code and is some core concept in your domain. Think smaller. A ten line class is totally valid. Make little classes where you see they make sense (a Date, a MailingAddress) and then work your way up by composing classes out of those.
As you start to partition little pieces of your codebase into classes, the remaining procedural code soup will shrink. In that shrinking pool, you'll start to see other things that can be classes. Continue until the pool is empty.
How many OOP programmers does it take to change a light bulb?
None, the light bulb changes itself.
;)
You can play around with an OO language that has very bad procedural support like Smalltalk. The message sending paradigm will force you into OO thinking.
i think you should start it with a good plan.
planning using CLASS Diagrams would be a good start.
you should identify the ENTITIES needed in the applicaiton,
then define each entitie's ATTRIBUTES, and METHODS.
if there are repeated ones, you could now re-define your entities
in a way that inheritance could be done, to avoid redundancy.
:D.
I have a three step process, this is one that I have gone through successfully myself. Later I met an ex-teacher turned programmer (now very experienced) who explained to me exactly why this method worked so well, there's some psychology involved but it's essentially all about maintaining control and confidence as you learn. Here it is:
Learn what test driven development (TDD) is. You can comfortably do this with procedural code so you don't need to start working with objects yet if you don't want to. The second step depends on this.
Pick up a copy of Refactoring: Improving the Design of Existing Code by Martin Fowler. It's essentially a catalogue of little changes that you can make to existing code. You can't refactor properly without tests though. What this allows you to do is to mess with the code without worrying that everything will break. Tests and refactoring take away the paranoia and sense that you don't know what will happen, which is incredibly liberating. You left to basically play around. As you get more confident with that start exploring mocks for testing the interactions between objects.
Now comes the big that most people, mistakenly start with, it's good stuff but it should really come third. At this point you can should reading about design patterns, code smells (that's a good one to Google) and object oriented design principles. Also learn about user stories or use cases as these give you good initial candidate classes when writing new applications, which is a good solution to the "where do I start?" problem when writing apps.
And that's it! Proven goodness! Let me know how it goes.
My eureka moment for understanding object-oriented design was when I read Eric Evans' book "Domain-Driven Design: Tackling Complexity in the Heart of Software". Or the "Domain Driven Design Quickly" mini-book (which is available online as a free PDF) if you are cheap or impatient. :)
Any time you have a "Manager" class or any static singleton instances, you are probably building a procedural design.