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I am coming from the Embedded Systems domain with more than 3 years experience.
In my current project, at the beginning, I was only responsible for only software development and the Team consisted of 3 people.
But, as time passes, hardware eng. and project lead eng. left the job respectively. So far, the project moved with a zero- architecture documentation to give an output as fast as possible. Later, new project lead took over the project and started from the begining with applying V-model. We started to create product specs->HLR->DLR on EXCEL. But now, He left the job too :). Now, I am alone on my way with nearly 700 pieces of well written product requirements. Anyway, I started to gathering and classfying requirements as non-functional, functional, business, stakeholder etc. As gathering non-functionals, I also classified them scalability, performance, regulatory, design contrains etc. So far, I did not draw any use-case. Please verify me here, what I know is that input of use-case are functional requirements. So, I created a use-case cards and now I am planning to write use-case cards for each functional requirements then also write a sequence diagram for each use-case card. Now till here, am I going right ? Does notations used in use-case such as include, extend etc. help me to create class diagram ? Is this also right way ?
Can classes be derived from use-cases?
When Ivar Jacobson invented use-cases he aimed at a development method that would be driven by the use-cases and allow to methodically derive the implementation from the use cases. That was his vision end of the 80s. His first attempt was called Objectory, which was bought by a larger company and lead to Rational Unified Process, which was generalized to be less proprietary into the Unified Software Development Process (Unified Process, or UP in short).
There is in particular one practice that allows to translate a use-case into classes: the Entity Control Boundary approach: use-cases become «control» classes, links between use-cases and actors become «boundary» classes, and «entity» classes are created for the business objects identified in (or derived from) the use-case narratives.
Once these first candidate classes are modelled, further work is undertaken during the design and classes may get reorganized to best fit into the solution (e.g. several boundary classes are regrouped for designing the GUI, and may thereafter be decomposed into UI elements, etc...).
But is this the best approach in your case?
UP is iterative and incremental, and fits well into modern version of the V-model, since the early iterations of the elaboration phase aim to stabilize the architecture and teh components (or sub-systems).
However, this may be a very time-consuming approach, especially considering the huge number of use-cases that you have. If you look at all the questions that modelling a use-case usually raises, especially if you add «include» and «extend», you risk to spend a lot of time (more than 300 days?) to draw robust use-case diagrams. And then, using ECB, your requirements might be outdated before you finish the design!
Alternatives
On the other side, some non-academic authors claim that every system has 3 to 5 really main use-cases: as a user I don't have 700 goals for using a system. So you'd better identify these and see how they relate. It's probable that many of the other requirements are far too detailed and could easily be assigned as additional information for the main use-cases.
In a similar thought, Ivar Jacobson has adapted his method to the current software engineering reality, with the use-case 2.0 approach. Don't misunderstand me, the UML would still be the same, but ECB no longer appears (modern frameworks influence much more the design of the boundaries than the use-case model, and entities are modelled using more focused approaches, such as DDD).
The idea behind use-case 2.0 is to slice the main use-cases into several smaller parts and start to develop something that makes sense for the user and can then be further refined.
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In Eric Evans book on domain driven design it is written:
Domain modeling is not a matter of making as “realistic” a model as
possible. Even in a domain of tangible real-world things, our model is
an artificial creation. Nor is it just the construction of a software
mechanism that gives the necessary results.
Now I have two questions:
Should a model be designed
somehow that it could evolve to a more
realistic shape whenever NEEDED
without touching the core model in previous iteration?
If the answer to the previous question is positive, where can I learn how to create realistic core models?
Again if the answer to the question one is possible, would a day come that our model reflects any problem in the world?
Domain Model should not reflect real world.
It should only show one point of view depending on the context.
Let's say we got a glass.
One may think, well it's a glass and we can fill it with water. It is used to drink.
Other may think, well it's a product and we can sell it.
Another one may say, glass an inventory item. I don't care how does it looks like, but how many glasses I got here.
Depending on the context, we model glass differently. Still it is the same glass, but means something else.
All information related to the subject you can find on Udi Dahan's blog.
And more in the subject of modeling reallity, can be found here Don’t try to model the real world, it doesn’t exist.
Should a model be designed somehow that it could evolve to a more realistic shape whenever NEEDED without touching the core model in
previous iteration?
No, a model should reflect the particular problem under consideration. If the underlying problem changes, the model should reflect it. Let's say your modeling a hotel reservation system, a warehouse system, or a store point-of-sale system, your model should be a representation of the current concepts in those domains and the interaction between them. Models are not versioned over time.
2 and 3
No.
In a problem domain, there are obvious things and hidden things.
If you just model the obvious, apparent notions (whether real world objects or intangible concepts), creating a class for each one, you will have a realistic model but it will miss the point. It won't be a deep, insightful domain model.
To go beyond mere realism, you should sit with a domain expert and try to discover the hidden things in the problem space that will be helpful to the solution space - your application.
For instance, talking to a railway traffic expert, you might uncover heuristics or properties in the way train departures and arrivals are orchestrated that even the expert didn't realize or put a name on before. Naming these things will allow you to reason about them and ultimately act on them in your application. Or, you might have an elephant in the room - a big, widely used historical concept - and decide to reject it from your ubiquitous language because it doesn't describe a subpart of the problem accurately enough.
Realistic here is meant as opposed to refined, rationalized, not to totally made-up.
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I am working on an open-source project which shows how to develop software iteratively using test-driven development and some ideas from domain-driven design. I know what I would do, however my formal skills (especially regarding UML) are a little bit rusty.
Below I am going to post my first steps with the diagrams and the explanations I would give to my readers.
I have the following questions:
The last step ends with the question But what will stich together these components?. How to show the reader the way in UML terms, while not skipping anything in the train of thought? What I plan to do is to let each component provide an Environment class. For the purpose of testing, a TestingEnvironment will gather all those environments and inject the right callbacks into the World. But which types of UML diagrams to use for showing my train of thought, and in which order? My problem is, somehow, that I know what I want to do, but I can't rationalize it to myself why I want to do it that way - I guess it has gotten a part of me to the point I don't make such decisions consciously any more.
What mistakes have I done so far, how to fix them, and most importantly: WHY?
Step 1
(0001_user_commands_use_cases.pdf)
(0002_user_commands_use_cases.pdf)
User Use Cases - Analysis
We are starting with an use case diagram (0001_user_commands_use_cases.pdf) as
part of the preliminary analysis stage. This diagram should only help us
understand what our client wants. These use cases may change over time, but
never the less, they help us understand the system we are going to develop.
Please follow the arrows while reading the following explanations.
The role the user plays when interacting first with our system will be Guest.
The Guest sends to the system some registration data, which we process.
In the diagram, we are describing what happens from a logistic point of view,
from the perspective of the client for which we write the application. We are
not referring yet to classes or objects, or the concrete workflow, which may
end up being quite different.
We are also not dealing with errors, because that would only add more
background noise to the idea - and because error handling does not add business
value to the system. Of course, a system has to be robust to errors, but keep
in mind that we're now just making the analysis - not the design of the system.
Logistically speaking, after the Guest has sent us the registration data, there
is a Registered User. A registered user can send us the login data, so that he
becomes an Authenticated User.
Following the diagram, we can see how only an Authenticated User can send to us
a request to log out of the system, thus becoming a Deauthenticated User.
Why a Deauthenticated User, and not a Guest back again? Basically, it comes
down to us not being able to foresee the future. We really have no idea how the
client will want us to extend the system - nor does he himself! Beside that,
the two roles, a Guest which we know nothing about, and a user which has just
deauthenticated, which we do know something about, are really different things.
Of course it may be that the Deauthenticated User will exist in our application
only for a very short period of time, or it may be that it's created for the
sole purpose of being destroyed back again, without being looked at by any
other subsystem of our ERP - but still I cannot stress it enough: logistically,
the role of a Deauthenticated User stands on its own.
The second diagram (0002_user_commands_use_cases.pdf) contains all the
information of the first diagram, with some added items. If you follow the
green arrows, you will see that the process is the same.
In the first diagram we notice how all three things done by the ERP system are
some kind of generalizations of a process. We have introduced this new generic
process in the second diagram as "Process Data".
Another element we have added in the second diagram is a generalization of the
three "Sending Data" elements. We are not sure how this will materialize in the
next stage (designing the system), but it looks like there's a generalization
there which may, in the end, make the system easier to maintain and extend.
We always seek new generalizations and abstractions because they have this nice
property of making the code maintainable and extendable.
Conclusion
----------
In our design, the ERP will do one central thing, "Process Data", data which
will come in in a standardized way, represented in our second diagram by the
"Send Data" use case.
We don't know how we will design these things yet, until now we have only
thought about the logistics, since we are doing just the analysis.
In the next commit, we are going to look closer at the application domain, in
order to better see the relations between all these notions and to enable us to
come up with a cohesive design.
Step 2
A rough overview of the components in the context of the application domain
Before looking at the diagram, let me first explain the thoughts I had prior to
coming up with this diagram.
We are going to design an ERP. What is this all about, and where lies the
business value in it?
We are supposedly making the product for a company which makes money by sending
products back and forth. This is the core domain of the application.
The basic idea is that a product P is moved from point A to point B, and in
this process, the company makes money.
The application will allow the company to make money by both being good at
organizing the workflow, and by making an existing workflow cheaper.
Let's say a product can be delivered to point C by taking the route A -> B ->
C, or the route A -> D -> C. The ERP must be capable of deciding which one is
better (in terms of money or time), and must manage the workflow it chooses.
So the whole point is supporting the movement of products around. Around what?
Around the world.
For this reason, let's first draw our first component: the World.
In a real project, I would continue by adding a Product component. I've chosen
not to yet, because this project is an educational one in nature, and I wanted
to get across new ideas about the architecture. If I had focused on the
products, I think there would be too much noise for the type of audience this
project is aimed at, a noise which would make the process of creating the
architecture and the architecture itself harder to understand.
We will introduce a Product component later, when the reader will feel at ease
with the architecture which, at that point, he will feel familiar with.
Instead of focusing on Products, we are going to focus on Users. This is,
incidentally, also the subject of the use cases we have drawn in the previous
commit. I think that any reader can relate to the concept of User.
So let's draw that component, the User.
Architecturally speaking, it's not that much of a difference between an User
and a Product. Instead of having Products moving around, we will have (for
now), users who live in the World and take different roles while interacting
with our system.
In the previous commit, we have concluded that there would be a standard way of
passing in data from the User to the system.
In terms of DDD (Domain-Driven Design), the data that gets into the system is
packed up as a Command. Since it looks like a good name, let's make a port of
the World component called Command Hub which will be used to receive and
process Commands from the outside.
Conceptually, the Command Hub will provide a Command Interface which any other
component can implement in order to send commands to the Hub, if it needs to.
We also want to make the components decoupled and thus reusable in different
types of applications, or to be able to combine them. This is achieved by
making an event-driven architecture.
For this reason, let's give the World component an Event Hub, which will
provide an Event interface.
But what will stich together these components?
This question is so pressing, because it's so central to our architecture, that
we will have to further investigate it.
This is not an asnwer, just a comment that would not fit into the comment box
(1) if you want to "teach your readers" something you can't do yourself, it is strange approach. Show your readers the way which works for you. Show the way "your train of thoughs runs", show the the mental images you saw in your mind, paper/pencil/photo in whatever visualization language you use
(2) you're skipping the uml-diagrams: UML 2.5 Behavior Diagrams as not useful? Even the uml-diagrams.org: UML Interaction Overview Diagrams not useful?
(3) this question looks like too broad(long) perhaps opinion-based and perhaps off-topic much more suitable for https://softwareengineering.stackexchange.com/help/on-topic
(4) for the recommended modeling workflow look at
(4.1) Cangnus's sequence diagramming comment in Stack Overflow: sequence diagram for books exchange
(4.2) BobRodes's use case scenario comment in Stack Overflow: Formal language for UML sequence diagrams
(4.3) Scott W. Ambler's Agile Modeling: Where Do I Start? for what when how and why Agile Modeling Best Practices
to name just a few
In conclusion of this my long comment, I don't see any mistakes you did. If this is description of how Test-driven Development and Domain-driven design works for you so well that you even use it subconsciously then it is just fine and ok. Being a good teach is not an easy task, good luck
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I have a scenario which involves a vending machine and then asks us to create to "model the problem domain". I've covered modelling very loosely and was hoping someone would clear this up.
From research it looks like a problem domain is just a domain model which in turn is pretty much a UML Class Diagram.
The examples I've seen look they're almost database schemas with a customer entity, order entity etc etc.
I'm just not sure what the differences are exactly.
So I just wondered if I was on the right track and would anyone mind elaborating on this or perhaps pointing me towards a concise definition. Thanks.
The "problem domain" is just the stuff you're interested in. In your case, it's all the stuff a vending machine does, and who interacts with it.
It boils down to a collection of use cases, which can be diagrammed in a use case diagram. What does the vending machine do? It takes coins from a buyer (the actor), gives change (maybe...so make sure you understand "extension points"), spits out stuff (always, because we aren't in the real world), and so on. Then maybe you can get creative with a different actor. A maintenance person takes out money, adds change, fills up the machine, runs a diagnostic stack, whatever. Each one of these is a use case. Put them together into a use case diagram.
If you want to go into detail about what each use case does, then use an activity diagram. One for each use case.
Any system (software or not and modeled or not) has structural and behaviour aspects.
The structural aspects are non-time bound aspects of your system, such as which classes your system is made up of, their associations and dependencies, how they are divided into subsystems, etc. Most of these elements are often referred to as classifiers.
The behaviour aspects shows how these structural aspects collaborates together over time to achieve the goals of the system, such as methods, state machines, workflows, use case realisations, etc.
The structural and behaviour aspects are what you specify when you are writing your code or creating a model.
Objects, are by definition instances of classes. This means that objects are the "things" that actually exists when the system executes. Hence, you do not program an object; you program a class, which when executed, is instantiated into one or several objects.
However, in many modelling languages (but not common in programming languages), you can also model specifications of scenarios, which show specifications of objects and how they interact, for example in UML you may create an object diagram, showing one example of how the system of objects (i.e., instantiated classes) might be structured and collaborate during execution.
Now, a system always strives to a achieve one or several goals for it's surrounding. The surrounding is made up of persons and/or another systems (actors) interacting with the system. This "surrounding" or "background", on which the system is situated in and makes sense in, is often called the "domain".
These "actors" have a "problem" they would like that the system helps them to solve. When this problem is modelled, one calls that model the "problem domain model" for the system. It states the logical structural and behaviour aspects of the problem domain, without stating how it is going to be implemented in a specific implementation of a system. I.e., it is not referring to implementation aspects, like Java, SQL, primary keys, transactions, reflection, angular, etc; it is instead focusing on the core structures of the domain, like Orders, Parties, Contracts, Products, etc.
The problem domain model is one of the most important "contracts" between the system developers and the persons paying for the system or being owners and users of the system. It makes it possible for you all to understand the problem to be solved in the same way and are makes sure that you all are using the same concepts to reason about it. Since it, by definition, is not a technical artefact, you should describe it using as simple notation (but still stringent and crisp clear) as possible so that also non-software professionals could understand and agree on it. Class diagrams (stripped from all technical details) and use case diagrams are two notation techniques available. But also object diagrams and activity diagrams could come in handy.
If you are interested in this, I deliver a course in advanced concept domain modeling on Udemy. Here is link and 90%-off code: https://www.udemy.com/get-your-concepts-straight/?couponCode=CONCEPTS29
Regards
Per
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In software engineering there are two main concepts in design phase which are abstraction and decomposition but I can't get the differences between them?
Both concepts are analysis & design basic techniques. There are interrelated and normally used together during software development. We use them even though we are not always aware of it. Deeper understanding of these concepts helps to be more accurate and effective in A&D.
Abstraction in general is process of consciously ignoring some aspects of a subject under analysis in order to better understand other aspects of it. In other words, it kind of simplification of a subject. In software in particular, analysis & design are all about abstraction.
When you model your DB, you ignore UI and behavior of your system and concentrate only on DB structure.
When you model your architecture, you concentrate on high-level modules and their relationships and ignore their internal structure
Each UML diagram for example gives a special, limited view on the system, therefore focusing on a single aspect and ignoring all other (sequences abstract objects and messages, deployment abstracts network and servers, use cases abstract system users and their interactions with a system, etc)
writing source code in any programming language requires a lot of abstraction - programmers abstract app's functionality using limited set of language constructs
Decomposition is an application of the old good principle "divide and conquer" to software development. It is a technique of classifying, structuring and grouping complex elements in order to end up with more atomic ones, organized in certain fashion and easier to manage. In all phases there are lots of examples:
functional decomposition of a complex process to hierarchical structure of smaller sub-processes and activities
high-level structure of an complex application to 3 tiers - UI, logic and data.
Class structure of a complex domain
namespaces as a common concept of breaking a global scope into several local ones
UML packages are a direct use of decomposition on the model level - use packages to organize your model
Abstraction is somehow more generic principle than decomposition, kind of "father of all principles" :)
Abstraction is one of the fundamental principles of object oriented programming. Abstraction allows us to name objects that are not directly instantiated but serve as a basis for creating objects with some common attributes or properties.
For example: in the context of computer accessories Data Storage Device is an abstract term because it can either be a USB pen drive, hard disk, or RAM. But a USB pen drive or hard disks are concrete objects because their attributes and behaviors are easily identifiable, which is not the case for Data Storage Device, being an abstract object for computer accessories. So, abstraction is used to generalize objects into one category in the design phase. For example in a travel management system you can use Vehicle as an abstract object or entity that generalizes how you travel from one place to another .
Decomposition is a way to break down your systems into modules in such a way that each module provides different functionality, but may affect other modules also. To understand decomposition quite clearly, you should first understand the concepts of association, composition, and aggregation.
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I'm starting a project with a team and we're using SCRUM as methodology. It's my first time with SCRUM. We have listed our functionalities and we made our stories, (user stories and technical stories as well as their tasks).
I've a tight UML approach to start any dev project and for me, after listing all the functionalities, the next step is to make the User Cases Diagram to let everybody see what's the application going to do and who's gonna interact with it. But my team said that there's no interest in using UML in SCRUM.
Can I use the User Diagram of UML to represent the User Stories in SCRUM? Which other diagrams can be used in SCRUM? (It could be a stupid question 'cause I cannot imagine an application without a class Diagram or a Sequence Diagram, but I really wanna see the advice from the experts in SCRUM)
Thanks.
Can I use the User Diagram of UML to represent the User Stories in SCRUM?
A use case diagram would be helpful, because it is pretty straightforward, and gives a high level idea what the project is about.
However I won't recommend to use any other UML diagram in scrum. I agree with the others that in an agile project the code changes so frequently that your diagrams will be obsolete after several days. In this case you have to redraw them, which is a waste.
For example if you are using eclipse for development, a simple refactoring step can ruin your class diagram :-(
Which other diagrams can be used in SCRUM?
I would suggest to use mindmaps. Recently we started to create our own user stories with drawing large mindmaps and put them on the office walls.
We have a feature in the middle, and we connect sub user stories to it - and sub-sub user stories to them -, and every available information we have at the moment. With this approach we have everything in one place: user stories, technical informations, questions, etc.
Of course the mindmap grows day by day, and we know more and more about the feature we have to implement.
Actually we are doing something similar described in this agile dzone article, but since you are using scrum not xp+kanban I talked about user stories not MMFs.
You can use whatever you like in Scrum that helps your team communicate effectively. Scrum makes no decisions, judgements, or guidance on what tools are effective for that team. It only asks that you reflect on the tools and practices used in executing a Sprint and make adjustments accordingly. This is the inspect and adapt loop.
Being open and honest in discussing the benefit of the tools and techniques used to deliver value requires a lot of effort and willingness by the individual members to be open to change.
What I've been told from people who've been using Scrum for a while (ie: this is opinion) is that doing UML diagrams can be a bit time consuming because as your development methodology is agile, your requirements could very easily radically change after the first sprint's show-and-tell, which means you could be doing fairly big redesigns.
Of course, do scratch up how you will tackle your tasks in the sprint backlog - you could certainly document as you go, but maintaining a central repository of class diagrams, etc. could be a slight waste in resources.
I'm not sure what's your role in the project, I'm supposing you are the PO. In that case, use additional documentation if it makes sense. Consider a user story as a reminder for the team to have a conversation with the PO about it.
If you think the user case diagram will clarify the functionality you are asking for, the it's ok. In fact, place it on the wall beside the scrumboard and burndown chart.
In my experience it is sufficient to specify for each story a "how to test" scenario. For example, suppose I have a story for Stackoverflow:
"As a user I can post a new question"
The "how to test" scenario could be:
"Click on a 'Ask Question' button, a form is displayed with a textarea for the question text and a textfield for tags. After the user enters both -they are mandatory- the user is redirected to the question list. The user can see the question title in the list, along with the tags"
So maybe a use case diagram is not really needed. I would recommend to try the "how to test" and see how it goes. It is very useful for the team because they know what you are expecting from the story, from a functional point of view. And you won't be doing documentation for every story.
If you don't like it, the go with the use case diagram, but it is a good idea to give the team something more than the story description.
Now, about the technical stories you mention. What are they? Why is a technical requirement mixed with the functional requirements? Maybe it IS a real requirement for the project, but usually it is not, and can be rewritten as a functional story. Unless your product is something like a framework or library.
For example, the technical story "create indices for the 'get questions' query" could be rewritten as "speed up the questions list page".
I only use class and sequence diagrams with Scrum because these two diagrams are live synchronized with the java code.
I certainly don't create UseCase or other diagrams or even try to generate code from diagram (e.g. MDD) because as soon as something is changed in my project and my code it is really too painful to update my diagrams. Diagrams should be automatically updated without any human intervention. I did many project with Omondo EclipseUML and it worked really well.
SCRUM is a application lifecycle management framework, not a methodology as you stated. Please refer to scrum.org
Use Cases are abstracted. If they help your team during refinement, then great. BUT once your team has committed to the story, change is welcomed and there is little point maintaining them once the story is done. The goal is always user acceptable working software!
UML state machine diagrams are useful in Scrum for projects focused on redesigning UI while retaining business logic:
State machine modeling is a dynamic modeling technique, one that focuses on identifying the behavior within your system-in this case, behavior specific to the instances of a single class. My style is to draw one or more state machine diagrams when a class exhibits different behavior depending on its state. For example, the Address class is fairly simple, representing data you will display and manipulate in your system. Seminar objects, on the other hand, are fairly complex, and therefore it makes sense to create a state machine diagram for them.
References
UML 2 State Machine Diagrams: An Agile Introduction