MVVM architecture for a Hardware based application - Design and Architecture Discussion Boards

It's about separating the different parts of the application for ease of maintenance. Microsoft has this site: http://www.asp.net/mvc[^] dedicated to it.

Use the best guess

K K Kodoth wrote:
Ive asked the same question to many architects but every body giving different different answers could any body tell me why this MVC,what is its advantage

You'll get as many answers as you'll get answerers Smile | :)

.
Richard's answer (above) is correct. MVC provides good separation of concerns, this is generally true where the MVC pattern is applicable.

But I'd like to add to Richard's answer. You need to look at ASP.Net forms applications. This was an attempt to coerce Winforms style programming onto web applications. Obviously this was reasonably successful (evidence: all the asp.net apps out there). It does however have drawbacks. The UI side of things is effectively hard to unit test (MVC is easy as there is no code-behind). ASP.NET forms "fights" the way the web works, it tries as far as possible to hide the request/response cycle from the dev, this can result in hiding the reality this model from the unwary (e.g. relative lack of awareness of the need to protect against values being hacked on the wire from submitted forms) and leads to relatively clunky code. Viewstate is another bugbear: it is there to support the forms mechanism by storing previous values etc, but it can get quite large if not managed properly. By contrast, ASP.NET MVC works with the web standards more closley e.g. values are no longer taken from winform-style elements but are just html form values and we can write handlers for the various HTTP request types on a particular path, working with the web. Other factors in asp.net MVC's favour is the razor syntax which is very clean and total control over the HTML created (you actually had this in ASP.NET form, but you had to work for it).

ASP.NET MVC does have drawback: the coding by convention does seem like magic sometimes (e.g. how form values are unpacked into the signature of the handling controller method). Additionally routing etc can be complex, but the consensus seems to be these are small losses for large gains.

“Education is not the piling on of learning, information, data, facts, skills, or abilities - that's training or instruction - but is rather making visible what is hidden as a seed”
“One of the greatest problems of our time is that many are schooled but few are educated”

Sir Thomas More (1478 – 1535)

Is there anything Related to performance improvement

Not performed any metric myself, but the general consensus is that MVC has better performance as there isn't the overhead of unpacking all the extra stuff (e.g. viewstate, control values) into the object graph that represents the page in asp.net forms. Here[^] is a fuller discussion on stackoverflow.

“Education is not the piling on of learning, information, data, facts, skills, or abilities - that's training or instruction - but is rather making visible what is hidden as a seed”
“One of the greatest problems of our time is that many are schooled but few are educated”

Sir Thomas More (1478 – 1535)

I have nearly finished anapplication with no formal methodology, but as things progress and the need to properly record and track things, I would like to make use of my chosen tracking system, TargetProcess. As it is I have my hands full getting to know all its features and coming to grips with defining my project through it, so I thought I'd ask for some help.

The app imports access control data for parking lots, from a third party (Impro). The data is basically when a driver swipes card at a terminal to enter or exit a zone in the car park. I then, by the grace of God, match entry and exit records to form VehiclePresence records. I apply a pricing table to VehiclePresence, to calculate amounts due for parking, and create BillingMessage objects which I send via API to a billing service (WHMCS).

There are some nasty edge cases, like when a driver enters via an open parking terminal (cheaper parking) and then enters through an internal terminal - without a real exit from the open terminal, and then exits through either. Another edge case is a power outage where booms are manually operated and entry and/or exit records are missing.

Now I can write many, many user stories for this application, but TargetProcess requires a feature for a user story, and that is where I battle. So far my rough draft of features is:

Parking access control.
Data import and vehicle movement database.
Processing and calculation and a vehicle presence database.
Billing
Security (not mentioned above, but goes without saying).
Configurability.
Reporting.
SMS and Email communications of important events.
Would you say thej above list is a roughly accurate feature breakdown of the app I describe earlier in the question? If far off, some advise on why would be appreciatd.

If you ask me, in a SCRUM context, that looks like a pretty crappy set of features. Maybe I need some epics at the top to narrow down the list, and more features below.

BTW, the puerile and mewling bunch of pricks on Programmers.StackExcgange.com closed this because it's "not a real question". I wish all StackExchange members had a mandatory reading comprehension test.

modified 17-Jun-13 3:52am.

According to User Story And Use Case Comparison[^] User Stories were invented to replace use-cases, where the developer spent ages writing a description that was too technical for business people. So [he] says to the business people: "Tell me the stories of what the system will do. Write down the name of the story and a paragraph or two."

It seems the whole point is Business writes the user stories to, critically, take ownership of them - so they stay interested and don't just say "it's too technical, I'll leave it to the developer" often with an accompanying "No, that's not what I wanted ..." because they've not got ownership.

So by that measure you shouldn't be writing the user stories.

By asking have you missed any User-Stories?, you first need to answer have you missed any Users?
I'd suggest drawing the use-cases with the actors to identify them. For example, as an Engineer Actor I'd say you should consider: Maintenance, Testing, and Proving. Then (quietly) use these as suggestions to the Business, bring up the suggestions and to make them think they were their ideas so they have some buy-in and can be persuaded that they have ownership.

I agree with Jonathan that you as a developer should not really be the Product Owner.
However, if you are both the Product Owner and the Team then you are the one to write the User Stories.

A User Story tells something of value to a user - that is why we can put a Business Value on it.

Here is an example from one of your bullet points: "Parking access control".
Ask Who and What and Why?
The answers are your user stories e.g.
"A Customer should be able to see how many free parking lots that are left when getting near a Parking Basement Entrance".
The why's do not need to be elaborated in the title, but you need them to determine a business value and the priority of the User Story (priority partially hinted by should[^])

You break this story into a number of tasks needed to fulfill the user story. Tasks are of whatever you need to do e.g. talk, purchase, seek, read, write, code, assemble, install, upgrade, etc.
The estimates of the tasks is the estimated cost of the user story. The business value and estimated cost gives you an estimated velocity; a number quite useful when you select user stories to put into a sprint.
When you complete a task, you log how much time you used on it. When all tasks for a user story are complete the business value with the total used time gets you the actual velocity.

The quality of your user stories dictate the quality of your estimated and actual velocity. A good user story has an obvious business value and is easy to break down into small set of simple tasks. A small set of simple tasks are easy to estimate and can be completed within a sprint. Hence, both estimated and actual velocity benefit from a good user story.

Kind Regards,

Keld Ølykke

Hi,

I need to architecture a WPF application that will interact with Hardware device(s).
I am planning to use MVVM architectural pattern and DI in order to provide modularity.

Here are the components of it.

Suppose we have a Hardware called as 'Car'.
There can be different type(s) of Car such as Ford, GM, Skoda etc.
The Cars will have features. Some of them are common to all the cars and some are specific to the Make and model.
Common features can be - 4 wheels, engine, steering etc.
Different features:
Ford - Music system, Auto lock etc.
GM - Automatic transmission, Power steering etc.
Skoda - Airbags, Antilock breaking system(ABS) etc.

Application should load screen according to the car.
The hardware will interact through a set of commands.
Each type of hardware will have their set of commands.
For E.g: Suppose total we have 50 commands for the all the types.
Supported commands by each type:
Ford - 30 out of 50
GM - 40 out of 50
Skoda - 20 out of 50.

I am planning to architect as shown below.

- An abstract class for the Car to interact with the hardware which will be a Model.
- Each type of Hardware/car will be another Model.
- There will be View-Model for each type of Car(Ford, GM and Skoda). We can have VM for different make of cars, if required.
- Similar to View-Model, we'll have Views(Screns).

I need to architect the Hardware Abstraction Layer(HAL).
By HAL, i mean to say a layer which will interact with the Hardware and should be extensible. So, in future if a new type of car comes, interaction with View-Models and Views should not change.
The HAL will be responsible of sending/receiving the commands.

A small representation of the MVVM architecutre will be as follows.

-----------------
| Car View |
-----------------
|
|---------------|-------------|
---------------- ----------- ------------
| Ford View | | GM View | | Skoda View |
---------------- ----------- ------------

-----------------
| Car ViewModel |
-----------------
|
|-----------------------|-------------|
----------------- -------------- -----------------
| Ford ViewModel | | GM ViewModel | | Skoda ViewModel |
----------------- -------------- -----------------

------------
| Car Model |
------------
|
|-----------|------------------|
-------------- ---------- --------------
| Ford Model | | GM Model | | Skoda Model |
-------------- ---------- --------------
|
-----------------------------------------------
| |
---------------------------------------- ---------------------------------------
| | | | | Hardware Abstraction Layer(HAL) | | Database Access Layer(DAL) |
| Send/Receive commands | | | | | | |
---------------------------------------- ---------------------------------------
|
|-----------------------|------------------------|
----------------- ----------------- ----------------------
| Actual Ford car | | Actual GM Model | | Actual Skoda Model |
---------------- ----------------- ----------------------

There will be DAL also, in order to work in offline mode.

I am thinking of having each type of car as a Module and there will be main part in the application wherein each of the modules will be loaded.
So, Ford Module will be have FordView, FordViewModel, FordModel.

Questions:
1- What could be the best way to architect such an application?
2- How can we bring modularity?
3- How can we bring extensiblity?
4- How does the interaction between different objects take place in a loosely coupled manner?
5- I'll be using Microsft Ribbon. How can we have interaction between different buttons in the Ribbon and modules or screens?
6- Any nice article/case study/link to understand the architecure.

Please let me know if any other information is required.

Appreciate the response and time.

Praveen Raghuvanshi wrote:
I am thinking of having each type of car as a Module

I would call it an adapter but yes that is it.

Praveen Raghuvanshi wrote:
2- How can we bring modularity

By using adapters.

Praveen Raghuvanshi wrote:
4- How does the interaction between different objects take place in a loosely
coupled manner?

Huh? Which "objects" do you think are interacting?

Praveen Raghuvanshi wrote:
5- I'll be using Microsft Ribbon. How can we have interaction between different
buttons in the Ribbon and modules or screens?

That isn't really a architecture question. And obviously if you want to look at that the first step would be to look at the API and figure out how it works and THEN attempt to answer your question.

Praveen Raghuvanshi wrote:
Please let me know if any other information is required

Figuring out exactly how and what you are going to persistence is going to be a significant problem.

Maybe you are already aware of ivi-systems, but you ought to check for existing efforts.

in-vehicle-infotainment-summit

Smile | :)

Questions:
1- What could be the best way to architect such an application?
Don't know particularly but whatever method you use do it thoughly
Consider your hardware being on a broadcast bus

2- How can we bring modularity?
First define what you mean by a module, h/w and s/w engineers have different ideas of what a module is I asked this on one project and the best answer I got was 'lego-like' - because it was on a project poster.
Once this was defined things started happening.

3- How can we bring extensiblity?
Again define it: work through a use case as to how you would extend the system. does a maintenance technician
take a new module and just plug it in? does it then need new software installed to accept new hardware or will the hardware deliver it or say where to get it etc

4- How does the interaction between different objects take place in a loosely coupled manner?
One possibility: Set up a message passing mechanism between objects and use a setup phase:
i.e. Tell Module A to do Task1 when it gets Message 1 and then send out Message 2 (but not till it's told to)
Tell Module B to do Task2 when it gets message 2 and then send out Message 3

and an execution phase:
Send Message 1 to Module A and wait for Message 2 from Module 2 to show completion.

5- I'll be using Microsft Ribbon. How can we have interaction between different buttons in the Ribbon and modules or screens?

Don't know offhand

6- Any nice article/case study/link to understand the architecure.
Look at http://en.wikipedia.org/wiki/CAN_Kingdom[^] described in more detail http://www.kvaser.com/images/Papers/ck301p.pdf[^]. The principles here allowed me to take a non-functioning 'modular' system and make it modular, extendable and above all work.

Appreciate your inputs!
I'll check on them.

Praveen Raghuvanshi
Software Developer

Guys, I am a software developer and want to improve my design skills.

Anybody suggest me some good books on Software Design and Architecture?

Thanks
MSR

See here[^].

Thank you Amarnath.

Right now I'm facing an issue I had faced much times, but now I decided go deep in it. (for our purpose, let's consider PHP with MySQL)
What's the most convenient method to get a collection of records from a database?

A) Query a collection of records and populate an array of objects through a loop, or

B) Execute a loop on an array where each object is initialized through his own method (with, of course, one query for each record)

A pros: less connections or data traffic.
A cons: duplicated code to retrieve same data, increasing maintenance.

B pros: a standar method to get data, minimizing maintenance.
B cons: most connections or data traffic.

I known that each option can be applied for each context, but I bring this question to a context where we have no idea of the future implications.

Please, give your opinion or suggestions, or tell me where I can find a publication specifically about this issue.

Thanks

I do not know the oddities of PHP. I'd go for getting all data from the database in one query, and then create the objects from those data: the communication overhead between the application sending the queries and the database is not zero, and with a database running on a different machine things may slow down terribly.
I do not understand why that should cause duplicated code - but that might be a php issue. In C#, methods can be written such that there is no duplicated code required.

That's the way I'm going on for a while: one query for all.
The duplicate code occurs cause you need one query to retrieve a collection and another query inside the class to retrieve data of a specific record. Both queries retrieve same fields, and if, for some reason, you need to change fields, you must change both queries.

Use a constant.

Bastard Programmer from Hell Suspicious | :suss:

If you can't read my code, try converting it here[^]

hmmm.. It can be an option.

Next time, you can post in the PHP forum.
It might get more people to answer your question.

Apps - Color Analyzer | Arctic | XKCD | Sound Meter | Speed Dial

I was doubted about the right place to post. This question is not specifically about PHP. I know how to do it. PHP is given just as an example. My doubt is about the best method, whatever language we could use.

Paulo S X Soares wrote:
A cons: duplicated code to retrieve same data

Whatever you mean by that it isn't happening unless you are doing something wrong.

Let's see an example.
I already have the class clsUser. The class has the GetData method, used to retrieve data and fill an $User instance.

$User=new clsUser;
$Result=$User->GetData($ID);

In GetData method there is a query like "select ID,Name,Type,etc... from Users where ID=".$ID.
In other point of the application, I need a list ou users for some purpose. I use a query like "select ID,Name,Type,etc... from Users where <whatever>". See that the fields list is the same in both queries. That's what I call duplicated code.

Paulo S X Soares wrote:
n other point of the application, ...That's what I call duplicated code.

The you should be using a database layer with appropriate idioms - which would avoid that.