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• Component-based design: handling objects interaction

  - by Milo

  I'm not sure how exactly objects do things to other objects in a component based design. Say I have an Obj class. I do: Obj obj; obj.add(new Position()); obj.add(new Physics()); How could I then have another object not only move the ball but have those physics applied. I'm not looking for implementation details but rather abstractly how objects communicate. In an entity based design, you might just have: obj1.emitForceOn(obj2,5.0,0.0,0.0); Any article or explanation to get a better grasp on a component driven design and how to do basic things would be really helpful.

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• Distributed Transaction Framework across webservices

  - by John Petrak

  I am designing a new system that has one central web service and several site web services which are spread across the country and some overseas. It has some data that must be identical on all sites. So my plan is to maintain that data in the central web service and then "sync" the data to sites. This includes inserts, edits and deletes. I see a problem when deleting, if one site has used the record, then I need to undo the delete that has happened on the other servers. This lead me to idea that I need some sort of transaction system that can work across different web servers. Before I design one from scratch, I would like to know if anyone has come across this sort of problem and if there are any frame works or even design patterns that might aid me?

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• Is event sourcing ready for prime time?

  - by Dakotah North

  Event Sourcing was popularized by LMAX as a means to provide speed, performance scalability, transparent persistence and transparent live mirroring. Before being rebranded as Event Sourcing, this type of architectural pattern was known as System Prevalence but yet I was never familiar with this pattern before the LMAX team went public. Has this pattern proved itself in numerous production systems and therefore even conservative individuals should feel empowered to embrace this pattern or is event sourcing / system prevalence an exotic pattern that is best left for the fearless?

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• Register Game Object Components in Game Subsystems? (Component-based Game Object design)

  - by topright

  I'm creating a component-based game object system. Some tips: GameObject is simply a list of Components. There are GameSubsystems. For example, rendering, physics etc. Each GameSubsystem contains pointers to some of Components. GameSubsystem is a very powerful and flexible abstraction: it represents any slice (or aspect) of the game world. There is a need in a mechanism of registering Components in GameSubsystems (when GameObject is created and composed). There are 4 approaches: 1: Chain of responsibility pattern. Every Component is offered to every GameSubsystem. GameSubsystem makes a decision which Components to register (and how to organize them). For example, GameSubsystemRender can register Renderable Components. pro. Components know nothing about how they are used. Low coupling. A. We can add new GameSubsystem. For example, let's add GameSubsystemTitles that registers all ComponentTitle and guarantees that every title is unique and provides interface to quering objects by title. Of course, ComponentTitle should not be rewrited or inherited in this case. B. We can reorganize existing GameSubsystems. For example, GameSubsystemAudio, GameSubsystemRender, GameSubsystemParticleEmmiter can be merged into GameSubsystemSpatial (to place all audio, emmiter, render Components in the same hierarchy and use parent-relative transforms). con. Every-to-every check. Very innefficient. con. Subsystems know about Components. 2: Each Subsystem searches for Components of specific types. pro. Better performance than in Approach 1. con. Subsystems still know about Components. 3: Component registers itself in GameSubsystem(s). We know at compile-time that there is a GameSubsystemRenderer, so let's ComponentImageRender will call something like GameSubsystemRenderer::register(ComponentRenderBase*). pro. Performance. No unnecessary checks as in Approach 1. con. Components are badly coupled with GameSubsystems. 4: Mediator pattern. GameState (that contains GameSubsystems) can implement registerComponent(Component*). pro. Components and GameSubystems know nothing about each other. con. In C++ it would look like ugly and slow typeid-switch. Questions: Which approach is better and mostly used in component-based design? What Practice says? Any suggestions about implementation of Approach 4? Thank you.

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• SceneManagers as systems in entity system or as a core class used by a system?

  - by Hatoru Hansou

  It seems entity systems are really popular here. Links posted by other users convinced me of the power of such system and I decided to try it. (Well, that and my original code getting messy) In my project, I originally had a SceneManager class that maintained needed logic and structures to organize the scene (QuadTree, 2D game). Before rendering I call selectRect() and pass the x,y of the camera and the width and height of the screen and then obtain a minimized list containing only visible entities ordered from back to front. Now with Systems, originally in my first attempt my Render system required to get added all entities it should handle. This may sound like the correct approach but I realized this was not efficient. Trying to optimize It I reused the SceneManager class internally in the Renderer system, but then I realized I needed methods such as selectRect() in others systems too (AI principally) and make the SceneManager accessible globally again. Currently I converted SceneManager to a system, and ended up with the following interface (only relevant methods): /// Base system interface class System { public: virtual void tick (double delta_time) = 0; // (methods to add and remove entities) }; typedef std::vector<Entity*> EntitiesVector; /// Specialized system interface to allow query the scene class SceneManager: public System { public: virtual EntitiesVector& cull () = 0; /// Sets the entity to be used as the camera and replaces previous ones. virtual void setCamera (Entity* entity) = 0; }; class SceneRenderer // Not a system { vitual void render (EntitiesVector& entities) = 0; }; Also I could not guess how to convert renderers to systems. My game separates logic updates from screen updates, my main class have a tick() method and a render() method that may not be called the same times. In my first attempt renderers were systems but they was saved in a separated manager, updated only in render() and not in tick() like all other systems. I realized that was silly and simply created a SceneRenderer interface and give up about converting them to systems, but that may be for another question. Then... something does not feel right, isn't it? If I understood correctly a system should not depend on another or even count with another system exposing an specific interface. Each system should care only about its entities, or nodes (as optimization, so they have direct references to relevant components without having to constantly call the component() or getComponent() method of the entity).

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• Transmitting Form Data from the Client to the Web Server

  The steps involved in transmitting form data from the client to the web server User loads web form User enters data in to web form fields User clicks submit On submit page validates fields using JavaScript. If validation errors are found then the validation script stops the browser from canceling posting the data to the web server and displays error messages as needed If the form passes the data validation process then the browser will URL encode the values of every field and post it to the server.  The server reads the posted data from the query string and then again validates the data just to ensure data consistency and to prevent any non-validated data because JavaScript was turned off on the clients browser from being inserted in to a database or passed on to other process If the data passes the second validation check then the server side code will continue with the requested processes

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• How to decide whether to implement an operation as Entity operation vs Service operation in Domain Driven Design?

  - by Louis Rhys

  I am reading Evans's Domain Driven Design. The book says that there are entity and there are services. If I were to implement an operation, how to decide whether I should add it as a method on an entity or do it in a service class? e.g. myEntity.DoStuff() or myService.DoStuffOn(myEntity)? Does it depend on whether other entities are involved? If it involves other entities, implement as service operation? But entities can have associations and can traverse it from there too right? Does it depend on stateless or not? But service can also access entities' variable, right? Like in do stuff myService.DoStuffOn, it can have code like if(myEntity.IsX) doSomething(); Which means that it will depend on the state? Or does it depend on complexity? How do you define complex operations?

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• Broad topics needed for teaching game development

  - by livingtech

  I am going to be doing a presentation on game development to an iPhone user group in the near(ish) future. My audience are iPhone developers, but not necessarily very experienced ones, and this is meant to be an introduction. My question is, what broad topics are needed to understand game development? I acknowledge that this is fairly subjective, but I really am hoping for a comprehensive list of high-level topics that apply to a broad enough swath of games that anyone interested in the topic SHOULD know about them. I would be ecstatic with some pointers to any resources that attempt to make a list such as this this. (I have looked, but my google-fu is failing me tonight.) Here's what I have so far: The Game Loop a sub-note about event driven games 2D Animation sprites/texture maps 3D Animation importance of frameworks modeling software Particles and particle effects hit detection AI Obviously I will not be covering all these topics with any depth, more like simply defining them so that after my talk, the audience will (hopefully) be able to wrap their heads around how any given game might be developed. What am I missing?

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• Frames per Second and Updates per Second [on hold]

  - by matt murray

  So this is more a general resources question, as I am seeking knowledge on how best to conserve resources in a game (I am writing in Java, and please this is not a thread on what language I should write it in, I have already chosen Java) so that the updates and frames per second could be the highest they could be. In general I am just searching for any articles you may have, any personal experience, anything what so ever that could be of use to a pretty new Java game developer on the subject! Thanks in advance!

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• Entity Component System for HUD and GUI

  - by Jason L.

  This is a very rough sketch of how I currently have things designed. It should, at least, give an idea of how my ECS is currently designed. If you notice in that diagram, I have basically split the HUD out of the ECS. They have their own set of things (HudLayer, HudComponent, etc) and are handled differently. This is where I'm struggling, though. There are many different instances in which the HUD will need to know about entities. Not just data changing (I have an event dispatcher for that), but the actual entity and all it encompasses. There are also situations where entities will need to be able to query the HUD for data. Let's take a couple examples: First, my equipment screen. On here I can change the equipment on a character (Entity). In order for this to happen, I need to know about the entity. At least I think I do? How can I handle this? The second scenario involves my Systems needing to query a HudComponent for data. A specific example would be my battle system. Each "team" is given a 3x3 grid they can move around in. See here: Skills target these cells, and not the player, so I would need a way for my systems to determine which cells are occupied and which are not. Basically I need a way for two way communication between Systems and my HUD. I know it's recommended (by some people, anyways) to take your HUD out of the ECS. Is that appropriate in my case?

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• Programming is easy, Designing is hard

  - by Rachel

  I work as Programmer and I feel if design documents are properly in place and requirements are clearly specified than programming is not that difficult but when I think in terms of Designing a Software than it gives chills to me and I think its a very difficult part. I want to develop my Design Skills so, How should I go about it ? Are there any books, blogs, websites or other approaches that SO community can suggest ? Update: By Design I meant Design of overall Application or particular problem at hand and not UI Design.

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• Use of Service Bus in a Pub-Sub Engine

  - by JoseK

  In one of our projects, we've built a Publisher - Subscriber Engine on Oracle Service Bus. The functionality being a series of events are published and subscribers (JMS queues) receive these whenever a new event is published. We are facing some technical issues now, performance-wise and hence an architectural review is underway. Now for my questions: Architecturally the ESB has to publish events into a DB and read from the DB which users wish to be notified, then push the event onto their respective queues. There is a high amount of DB interaction and the question is whether ESB should be having such high amount of interaction with the DB in the first place? Or should there have been some alternate component responsible for doing this. Alternately is there any non-DB approach in which we can store the events and subscribers? Where else can this application data be held within the ESB context?

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• Should I incorporate exit cost into choosing a solution

  - by Mr Happy

  I'm currently choosing between two viable software designs/solutions. Solution 1 is easy to implement, but will lock some data in a propriaty format, and will be hard to change later. Solution 2 is hard to implement, but will be a lot easier to change later on. Should I go YAGNI on this or should I incorporate the exit cost in the decision making? Or asked differently, is the exit cost part of the TCO? I'm thinking of going back to the customer with this to ask wether or not he thinks the exit costs are relevant, but I'd like to know what the community thinks first. P.S. Is exit cost the correct term?

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• Game editor integration with the engine?

  - by Daniel

  What I am trying to figure out is what is the best way to integrate the editor(level, effects, model, etc...) in the most effective way? Now the first thing I thought would be to create the game engine(*) extremely modular. For example I took the example of game states. You could have multiple game states that all have their own update() and draw() methods among others. Each game state class would inherit from a base GameState class. This allows for a more modular approach and a useful one at that. Now would the most efficient approach be to implement the editor along with the modular engine, or create two different designs for both the game, and editor? I thought to take the game state example and extend it to window states, and well could be used for a lot more systems. Is there a better implementation of this design(game state) for use in other systems used in the engine? *: Now I know the term game engine is sorta irrelevant, and misused in many situations. What I am referring to as the "game engine" is the combination of the systems that the game must interact with for short. Also this is more of a theory / design question than an implementation. Even though both mix, i'd rather like to have a more general idea on how the editor is built in an efficient way and still using the same engine code as what the game uses. Thanks, Daniel P.S If you need more clarification or extra bits just leave a comment.

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• How do I create my own programming language and a compiler for it

  - by Dave

  I am thorough with programming and have come across languages including BASIC, FORTRAN, COBOL, LISP, LOGO, Java, C++, C, MATLAB, Mathematica, Python, Ruby, Perl, JavaScript, Assembly and so on. I can't understand how people create programming languages and devise compilers for it. I also couldn't understand how people create OS like Windows, Mac, UNIX, DOS and so on. The other thing that is mysterious to me is how people create libraries like OpenGL, OpenCL, OpenCV, Cocoa, MFC and so on. The last thing I am unable to figure out is how scientists devise an assembly language and an assembler for a microprocessor. I would really like to learn all of these stuff and I am 15 years old. I always wanted to be a computer scientist someone like Babbage, Turing, Shannon, or Dennis Ritchie. I have already read Aho's Compiler Design and Tanenbaum's OS concepts book and they all only discuss concepts and code in a high level. They don't go into the details and nuances and how to devise a compiler or operating system. I want a concrete understanding so that I can create one myself and not just an understanding of what a thread, semaphore, process, or parsing is. I asked my brother about all this. He is a SB student in EECS at MIT and hasn't got a clue of how to actually create all these stuff in the real world. All he knows is just an understanding of Compiler Design and OS concepts like the ones that you guys have mentioned (i.e. like Thread, Synchronization, Concurrency, memory management, Lexical Analysis, Intermediate code generation and so on)

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• What tools, libraries, or framework is needed to create a completely offline Javascript application?

  - by makerofthings7

  I am interested in creating a HTML application that can run as disconnected from the server as possible. Two examples of this include OWA in Exchange 2013 and to a lesser extent and the client available at www.ripple.com With the focus on OWA in Exchange 2013, what is needed to replicate the offline functionality available in a different application? A list technologies, frameworks, etc would be immensely helpful

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• How to manage security of these self hosted web apis, to ensure that the request coming for accessing data is authenticated?

  - by Husrat Mehmood

  Let's pretend I am going to work on an enterprise application. Say I have 11 modules in the application and I would have to develop Dashboards for every role in the organization for whom I are going to develop application. We Decided to use Asp.Net Web Api and return json data from our apis. We are going to include 11 Self hosted web apis projects in our application (one self hosted web api) for every module. All 11 modules are connected to one Sql server 2012 Database. Then once api is ready we would have to create Business Dashboards (Based upon roles in Organization). So Now my web api client is Asp.Net Mvc application.Asp.Net mvc will consume those web apis. Here is the part for whom all explanation is done. How should I manage Security of all 11 self hosted web apis? How should I only authenticated request is coming? If I authenticate user by login and password and then redirect user to appropriate Dashboard designed for the role that user have and load data by consuming web apis. How should I ensure that the request coming for accessing data is authenticated?

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• Design Patterns and their most common uses for them [closed]

  - by cable729

  Possible Duplicate: What are some programming design patterns that are useful in game development? As I'm returning to game dev, I've realized that I've lost a lot of the knowledge I had before. So now I'm looking at design patterns that I can use for my next project. One design pattern that I've seen a lot is the 'composition method,' which uses actors and components. Is that the right name for it? I'd like to look more at this and see what the advantages/pitfalls are. So what design patterns are out there, and what are the advantages/disadvantages to them?

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• Adding sub-entities to existing entities. Should it be done in the Entity and Component classes?

  - by Coyote

  I'm in a situation where a player can be given the control of small parts of an entity (i.e. Left missile battery). Therefore I started implementing sub entities as follow. Entities are Objects with 3 arrays: pointers to components pointers to sub entities communication subscribers (temporary implementation) Now when an entity is built it has a few components as you might expect and also I can attach sub entities which are handled with some dedicated code in the Entity and Component classes. I noticed sub entities are sharing data in 3 parts: position: the sub entities are using the parent's position and their own as an offset. scrips: sub entities are draining ammo and energy from the parent. physics: sub entities add weight to the parent I made this to quickly go forward, but as I'm slowly fixing current implementations I wonder if this wasn't a mistake. Is my current implementation something commonly done? Will this implementation put me in a corner? I thought it might be a better thing to create some sort of SubEntityComponent where sub entities are attached and handled. But before changing anything I wanted to seek the community's wisdom.

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• How to design a scriptable communication emulator?

  - by Hawk

  Requirement: We need a tool that simulates a hardware device that communicates via RS232 or TCP/IP to allow us to test our main application which will communicate with the device. Current flow: User loads script Parse script into commands User runs script Execute commands Script / commands (simplified for discussion): Connect RS232 = RS232ConnectCommand Connect TCP/IP = TcpIpConnectCommand Send data = SendCommand Receive data = ReceiveCommand Disconnect = DisconnectCommand All commands implement the ICommand interface. The command runner simply executes a sequence of ICommand implementations sequentially thus ICommand must have an Execute exposure, pseudo code: void Execute(ICommunicator context) The Execute method takes a context argument which allows the command implementations to execute what they need to do. For instance SendCommand will call context.Send, etc. The problem RS232ConnectCommand and TcpIpConnectCommand needs to instantiate the context to be used by subsequent commands. How do you handle this elegantly? Solution 1: Change ICommand Execute method to: ICommunicator Execute(ICommunicator context) While it will work it seems like a code smell. All commands now need to return the context which for all commands except the connection ones will be the same context that is passed in. Solution 2: Create an ICommunicatorWrapper (ICommunicationBroker?) which follows the decorator pattern and decorates ICommunicator. It introduces a new exposure: void SetCommunicator(ICommunicator communicator) And ICommand is changed to use the wrapper: void Execute(ICommunicationWrapper context) Seems like a cleaner solution. Question Is this a good design? Am I on the right track?

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• Relationship between Repository and Unit of Work

  - by NullOrEmpty

  I am going to implement a repository, and I would like to use the UOW pattern since the consumer of the repository could do several operations, and I want to commit them at once. After read several articles about the matter, I still don't get how to relate this two elements, depending on the article it is being done in a way u other. Sometimes the UOW is something internal to the repository: public class Repository { UnitOfWork _uow; public Repository() { _uow = IoC.Get<UnitOfWork>(); } public void Save(Entity e) { _uow.Track(e); } public void SubmittChanges() { SaveInStorage(_uow.GetChanges()); } } And sometimes it is external: public class Repository { public void Save(Entity e, UnitOfWork uow) { uow.Track(e); } public void SubmittChanges(UnitOfWork uow) { SaveInStorage(uow.GetChanges()); } } Other times, is the UOW whom references the Repository public class UnitOfWork { Repository _repository; public UnitOfWork(Repository repository) { _repository = repository; } public void Save(Entity e) { this.Track(e); } public void SubmittChanges() { _repository.Save(this.GetChanges()); } } How are these two elements related? UOW tracks the elements that needs be changed, and repository contains the logic to persist those changes, but... who call who? Does the last make more sense? Also, who manages the connection? If several operations have to be done in the repository, I think using the same connection and even transaction is more sound, so maybe put the connection object inside the UOW and this one inside the repository makes sense as well. Cheers

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• Multiple sites with the same codebase in Python

  - by Jimmy

  I am trying to run a large amount of sites which share about 90% of their code. They are simply designed to query an API and return the results. They will have a common userbase / database but will be configured slightly different and will have different CSS (perhaps even different templating). My initial idea was to run them as separate applications with a common library but I have read about the sites framework which would allow them to run from a single instance of Django which may help to reduce memory usage. https://docs.djangoproject.com/en/dev/ref/contrib/sites/ Is the site framework the right approach to a problem like this, and does it have real benefits over running separate applications? Initially I thought it was, but now I think otherwise. I have heard the following: Your SITE_ID is set in settings.py, so in order to have multiple sites, you need multiple settings.py configurations, which means multiple distinct processes/instances. You can of course share the code base between them, but each site will need a dedicated worker / WSGIDaemon to serve the site. This effectively removes any benefit of running multiple sites under one hood, if each site needs a UWSGI instance running. Alternative ideas of systems: https://github.com/iivvoo/django_layers https://github.com/shestera/django-multisite I don't know what route to be taking with this.

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• Event Driven Communication in Game Engine - Yes or No?

  - by Bunkai.Satori

  As I am reading book Game Coding Complete (http://www.amazon.com/Game-Coding-Complete-Third-McShaffry/dp/1584506806/ref=sr_1_1?ie=UTF8&qid=1295978774&sr=8-1), the author recommend Event Driven communication among the all game objects and modules. Basicaly, all the living game actors and object should communicate with the key modules (Physics, AI, Game Logic, Game View, etc..) via internal event messaging system. This would mean designing efficient event manager as well. My question is, whether this is proven and recommended approach. If it is not properly designed, it might mean consuming a lot of CPU cycles, which can be used elsewhere. This is especially true, if the game is targetted for mobile platform. What is your opinion and recommendation, please?

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• Distributing an Android game with plugins via the market

  - by Peter Serwylo

  I'm new to Android development, and was wondering how the following could be achieved within the confines of the Android market as a distribution channel: One main application, which handles the main menu, networking, high scores, etc. Several games which can be launched from the main menu, which all work within the same eco system. The main application is not just a pseudo launcher for other games, these different games will share high scores and other achievements/preferences. In a traditional package management system such as apt, pacman or yum, this could be handled quite happily through dependencies. This does not appear to be possible via the Android market. The closest I've seen is when apps scan to check if the required app is installed, and if not, launches the market and asks the user to download the app. This sounds like a very messy solution. It also begs the question, would they download the game (plugin) first, which then downloads the main shell application? Or would they download the main shell application, and when they navigate to a menu item which says "Play game", then it scans for any installed games, and if none exist, redirects to the market? Also, I'm not even sure if it is possible to dig up the package from another application on the device, and start invoking classes from within (e.g. when you want to launch the game (plugin)) A final option is just to have a 3rd component which is a .jar that each game includes, which effectively contains the entire shell application. Then each game would appear to have the same menu, but it would become a nightmare as soon as you want to update the menu component and have to re-release each game. It would be especially worse if other people released games (plugins) based on the same framework and didn't update them. Is there any other options which I haven't thought of? Has anyone else solved this or seen a solution in any apps they've installed (doesn't have to be games)? cheers.

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• What is the most effective way to add functionality to unfamiliar, structurally unsound code?

  - by Coder

  This is probably something everyone has to face during the development sooner or later. You have an existing code written by someone else, and you have to extend it to work under new requirements. Sometimes it's simple, but sometimes the modules have medium to high coupling and medium to low cohesion, so the moment you start touching anything, everything breaks. And you don't feel that it's fixed correctly when you get the new and old scenarios working again. One approach would be to write tests, but in reality, in all cases I've seen, that was pretty much impossible (reliance on GUI, missing specifications, threading, complex dependencies and hierarchies, deadlines, etc). So everything sort of falls back to good ol' cowboy coding approach. But I refuse to believe there is no other systematic way that would make everything easier. Does anyone know a better approach, or the name of the methodology that should be used in such cases?

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