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  • Finding most Important Node(s) in a Directed Graph

    - by Srikar Appal
    I have a large (˜ 20 million nodes) directed Graph with in-edges & out-edges. I want to figure out which parts of of the graph deserve the most attention. Often most of the graph is boring, or at least it is already well understood. The way I am defining "attention" is by the concept of "connectedness" i.e. How can i find the most connected node(s) in the graph? In what follows, One can assume that nodes by themselves have no score, the edges have no weight & they are either connected or not. This website suggest some pretty complicated procedures like n-dimensional space, Eigen Vectors, graph centrality concepts, pageRank etc. Is this problem that complex? Can I not do a simple Breadth-First Traversal of the entire graph where at each node I figure out a way to find the number of in-edges. The node with most in-edges is the most important node in the graph. Am I missing something here?

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  • Inheritance vs composition in this example

    - by Gerenuk
    I'm wondering about the differences between inheritance and composition examined with concrete code relevant arguments. In particular my example was Inheritance: class Do: def do(self): self.doA() self.doB() def doA(self): pass def doB(self): pass class MyDo(Do): def doA(self): print("A") def doB(self): print("B") x=MyDo() vs Composition: class Do: def __init__(self, a, b): self.a=a self.b=b def do(self): self.a.do() self.b.do() x=Do(DoA(), DoB()) (Note for composition I'm missing code so it's not actually shorter) Can you name particular advantages of one or the other? I'm think of: composition is useful if you plan to reuse DoA() in another context inheritance seems easier; no additional references/variables/initialization method doA can access internal variable (be it a good or bad thing :) ) inheritance groups logic A and B together; even though you could equally introduce a grouped delegate object inheritance provides a preset class for the users; with composition you'd have to encapsule the initialization in a factory so that the user does have to assemble the logic and the skeleton ... Basically I'd like to examine the implications of inheritance vs composition. I heard often composition is prefered, but I'd like to understand that by example. Of course I can always start with one and refactor later to the other.

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  • Pattern for performing game actions

    - by Arkiliknam
    Is there a generally accepted pattern for performing various actions within a game? A way a player can perform actions and also that an AI might perform actions, such as move, attack, self-destruct, etc. I currently have an abstract BaseAction which uses .NET generics to specify the different objects that get returned by the various actions. This is all implemented in a pattern similar to the Command, where each action is responsible for itself and does all that it needs. My reasoning for being abstract is so that I may have a single ActionHandler, and AI can just queue up different action implementing the baseAction. And the reason it is generic is so that the different actions can return result information relevant to the action (as different actions can have totally different outcomes in the game), along with some common beforeAction and afterAction implementations. So... is there a more accepted way of doing this, or does this sound alright?

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  • Speaking this week at Richmond SQL Server User Group

    - by drsql
    Thursday night, at 6:00 (or so) I will be speaking in Richmond ( http://richmondsql.org/cs2007/ ), talking about How to Implement a Hierarchy using SQL Server. The abstract is: One of the most common structures you will come across in the real world is a hierarchy (either a single parent "tree" or a multi-parent "graph"). Many systems will implement the obvious examples, such as a corporate managerial structure or a bill of materials. It turns out that almost any many-to-many relationship can be...(read more)

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  • can you have too many dto/bo - mapping method

    - by Fredou
    I have a windows service, 2 web services and a web interface that need to follow the same path (data wise). So I came up with two ways of creating my solution. My concern is the fact that the UI/WS/etc will have their own kind of DTO (let's say the model in ASP.Net MVC) that should be mapped to a DTO so the SL can then map it to a BO then mapping it to the proper EF6 DTO so that I can save it in a database. So I'm thinking of doing it this way to remove one level of mapping. Which one should I take? Or is there a 3rd solution?

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  • Drawing large 2D sidescroller level terrain

    - by Yar
    I'm a relatively good programmer but now that it comes to add some basic levels to my 2D game I'm kinda stuck. What I want to do: An acceptable, large (8000 * 1000 pixels) "green hills" test level for my game. What is the best way for me to do this? It doesn't have to look great, it just shouldn't look like it was made in MS paint with the line and paint bucket tool. Basically it should just mud with grass on top of it, shaped in some form of hills. But how should I draw it, I can't just take out the pencil tool and start drawing it pixel per pixel, can I?

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  • Distinguishing between UI command & domain commands

    - by SonOfPirate
    I am building a WPF client application using the MVVM pattern that provides an interface on top of an existing set of business logic residing in a library which is shared with other applications. The business library followed a domain-driven architecture using CQRS to separate the read and write models (no event sourcing). The combination of technologies and patterns has brought up an interesting conundrum: The MVVM pattern uses the command pattern for handling user-interaction with the view models. .NET provides an ICommand interface which is implemented by most MVVM frameworks, like MVVM Light's RelayCommand and Prism's DelegateCommand. For example, the view model would expose a number of command objects as properties that are bound to the UI and respond when the user performs actions like clicking buttons. Many implementations of the CQRS use the command pattern to isolate and encapsulate individual behaviors. In my business library, we have implemented the write model as command / command-handler pairs. As such, when we want to do some work, such as create a new order, we 'issue' a command (CreateOrderCommand) which is routed to the command-handler responsible for executing the command. This is great, clearly explained in many sources and I am good with it. However, take this scenario: I have a ToolbarViewModel which exposes a CreateNewOrderCommand property. This ICommand object is bound to a button in the UI. When clicked, the UI command creates and issues a new CreateOrderCommand object to the domain which is handled by the CreateOrderCommandHandler. This is difficult to explain to other developers and I am finding myself getting tongue-tied because everything is a command. I'm sure I'm not the first developer to have patterns overlap like this where the naming/terminology also overlap. How have you approached distinguishing your commands used in the UI from those used in the domain? (Edit: I should mention that the business library is UI-agnostic, i.e. no UI technology-specific code exists, or will exists, in this library.)

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  • Victory rewards in digital CCG

    - by Nils Munch
    I am currently polishing a digital CCG where people can play against friend and random opponents in a classical Magic the Gathering-like duel CCG. I plan to award the players with 20 ingame currency units (lets call them gold) for each hour they are playing, 50 for each day they are playing and X for each victory. Now, the X is what I am trying to calculate here, since I would prefer keeping the currency to a certain value, but also with to entice the players to battle. I could go with a solid figure, say 25, for beating up an opponent. But that would result in experienced players only beating up newly started players, making the experience lame for both. I could also make a laddered tier, where you start at level 1, and raise in level as you defeat your opponents, where winning over a player awards you his level x 2 in gold. Which would you prefer if you were playing a game like this. There is no gold-based scoreboard, but the gold is used to purchase new cards along the way.

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  • Acceptable placement of the composition root using dependency injection and inversion of control containers

    - by Lumirris
    I've read in several sources including Mark Seemann's 'Ploeh' blog about how the appropriate placement of the composition root of an IoC container is as close as possible to the entry point of an application. In the .NET world, these applications seem to be commonly thought of as Web projects, WPF projects, console applications, things with a typical UI (read: not library projects). Is it really going against this sage advice to place the composition root at the entry point of a library project, when it represents the logical entry point of a group of library projects, and the client of a project group such as this is someone else's work, whose author can't or won't add the composition root to their project (a UI project or yet another library project, even)? I'm familiar with Ninject as an IoC container implementation, but I imagine many others work the same way in that they can scan for a module containing all the necessary binding configurations. This means I could put a binding module in its own library project to compile with my main library project's output, and if the client wanted to change the configuration (an unlikely scenario in my case), they could drop in a replacement dll to replace the library with the binding module. This seems to avoid the most common clients having to deal with dependency injection and composition roots at all, and would make for the cleanest API for the library project group. Yet this seems to fly in the face of conventional wisdom on the issue. Is it just that most of the advice out there makes the assumption that the developer has some coordination with the development of the UI project(s) as well, rather than my case, in which I'm just developing libraries for others to use?

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  • Updating an Entity through a Service

    - by GeorgeK
    I'm separating my software into three main layers (maybe tiers would be a better term): Presentation ('Views') Business logic ('Services' and 'Repositories') Data access ('Entities' (e.g. ActiveRecords)) What do I have now? In Presentation, I use read-only access to Entities, returned from Repositories or Services, to display data. $banks = $banksRegistryService->getBanksRepository()->getBanksByCity( $city ); $banksViewModel = new PaginatedList( $banks ); // some way to display banks; // example, not real code I find this approach quite efficient in terms of performance and code maintanability and still safe as long as all write operations (create, update, delete) are preformed through a Service: namespace Service\BankRegistry; use Service\AbstractDatabaseService; use Service\IBankRegistryService; use Model\BankRegistry\Bank; class Service extends AbstractDatabaseService implements IBankRegistryService { /** * Registers a new Bank * * @param string $name Bank's name * @param string $bik Bank's Identification Code * @param string $correspondent_account Bank's correspondent account * * @return Bank */ public function registerBank( $name, $bik, $correspondent_account ) { $bank = new Bank(); $bank -> setName( $name ) -> setBik( $bik ) -> setCorrespondentAccount( $correspondent_account ); if( null === $this->getBanksRepository()->getDefaultBank() ) $this->setDefaultBank( $bank ); $this->getEntityManager()->persist( $bank ); return $bank; } /** * Makes the $bank system's default bank * * @param Bank $bank * @return IBankRegistryService */ public function setDefaultBank( Bank $bank ) { $default_bank = $this->getBanksRepository()->getDefaultBank(); if( null !== $default_bank ) $default_bank->setDefault( false ); $bank->setDefault( true ); return $this; } } Where am I stuck? I'm struggling about how to update certain fields in Bank Entity. Bad solution #1: Making a series of setters in Service for each setter in Bank; - seems to be quite reduntant, increases Service interface complexity and proportionally decreases it's simplicity - something to avoid if you care about code maitainability. I try to follow KISS and DRY principles. Bad solution #2: Modifying Bank directly through it's native setters; - really bad. If you'll ever need to move modification into the Service, it will be pain. Business logic should remain in Business logic layer. Plus, there are plans on logging all of the actions and maybe even involve user permissions (perhaps, through decorators) in future, so all modifications should be made only through the Service. Possible good solution: Creating an updateBank( Bank $bank, $array_of_fields_to_update) method; - makes the interface as simple as possible, but there is a problem: one should not try to manually set isDefault flag on a Bank, this operation should be performed through setDefaultBank method. It gets even worse when you have relations that you don't want to be directly modified. Of course, you can just limit the fields that can be modified by this method, but how do you tell method's user what they can and cannot modify? Exceptions?

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  • What is the best wrapping strategy ?

    - by Riduidel
    Hi, I'm planning to integrate an external tool (ffmpeg in my particular case, but it could be anything, in fact, as lolng as its tasks are long running ones). This tool has a lot of command-line parameters. For now, I've done to simple things with it, already requiring me a good bunch of class writing, to embed all the information it can return to me. I now face the even more complex task of having to send it a bunch of parameters and to handle possible errors. So, what is a best way for that ? Create classes containing all possible options Relying upon a reverse equivalent of commons-cli / CliBuilder / OptionParser Directly write all options from user input Obiwan Kenobi powers (or anything I don't even know about) Please notice I do it in an uncommon language (for the sake of me, don't ask me what it is, as it looks like a desperate and sterile union between CoffeeScript and lua), as a consequence, there can be no framework doing what I want in the language I use.

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  • I know how to program, and how to learn how to program, but how/where do you learn how to make systems properly?

    - by Ryan
    There are many things that need to be considered when making a system, let's take for example a web based system where users log in and interact with each other, creating and editing content. Now I have to think about security, validation (I don't even think I am 100% sure what that entails), "making sure users don't step on each others feet" (term for this?), preventing errors in many cases, making sure database data doesn't become problematic through unexpected... situations? All these things I don't know how or where to learn, is there a book on this kind of stuff? Like I said there seems to be a huge difference between writing code and actually writing the right code, know what I mean? I feel like my current programming work lacks much of what I have described and I can see the problems it causes later, and then the problems are much harder to solve because data exists and people are using it. So can anyone point me to books or resources or the proper subset of programming(?) for this type of learning? PS: feel free to correct my tags, I don't know what I am talking about. Edit: I assume some of the examples I wrote apply to other types of systems too, I just don't know any other good examples because I've been mostly involved in web work.

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  • Game ideas for a platformer

    - by user5925
    I have created a platformer which currently has the features listed below. I would greatly appreciate any further ideas which I could implement! (I don't play a lot of games which is why I require help) -- Walking/jumping/movement -- player can shoot lasers -- enemies also walk, fly, and shoot lasers -- water (you can swim in this) -- mud (slows you down on contact, and stops you from jumping) -- ladders -- damage when falling from a large height, unless falling into water -- moving platforms -- springboards (jumping on them shoot you into the air) -- growing platforms (allow you to reach new places) -- key and door system -- gem and coin collection system

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  • MMORPG game balancing

    - by Gary Paluk
    I've seen a couple of examples of some game balancing techniques in books yet they are not comprehensive and not particularly aimed at MMORPGs but I'm looking for practical examples of game balancing techniques for MMORPGs. I am interested to know if anyone has documented the techniques used in popular games with proven success in this area. Ideally, any resource would cover most common types of stats and include layman mathematical models or techniques used to balance game mechanics found in advanced MMORPGs (I know it's a cliché, but WoW style) Any help would be great!

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  • Algorithmic Forecasting and Pattern Recognition

    - by Ryan King
    Say a user could enter project data into my software. Each project has 2 variables "size" and "work" and they're related but the relationship is not known. Is there a way to programmatically determine the relationship between the variables based on previous data and forecast the amount of work provided if only given the size of the project in the future? For Example, say the user had manually entered the following projects. Project 1 - Size:1, Work: 4 Project 2 - Size:2, Work: 7 Project 3 - Size:3, Work: 10 Project 4 - Size:4, Work: x What should I look into to be able to programmatically determine, that Work = Size*3+1 and therefor be able to say that x=13?

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  • Code Smell: Inheritance Abuse

    - by dsimcha
    It's been generally accepted in the OO community that one should "favor composition over inheritance". On the other hand, inheritance does provide both polymorphism and a straightforward, terse way of delegating everything to a base class unless explicitly overridden and is therefore extremely convenient and useful. Delegation can often (though not always) be verbose and brittle. The most obvious and IMHO surest sign of inheritance abuse is violation of the Liskov Substitution Principle. What are some other signs that inheritance is The Wrong Tool for the Job even if it seems convenient?

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  • Is having a class have a handleAction(type) method bad practice?

    - by zhenka
    My web application became a little too complicated to do everything in a controller so I had to build large wrapper classes for ORM models. The possible actions a user can trigger are all similar and after a certain point I realized that the best way to go would be to just have constructor method receive action type as a parameter to take care of the small differences internally, as opposed to either passing many arguments or doing a lot of things in the controller. Is this a good practice? I can't really give details for privacy issues.

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  • Should I cache the data or hit the database?

    - by JD01
    I have not worked with any caching mechanisms and was wondering what my options are in the .net world for the following scenario. We basically have a a REST Service where the user passes an ID of a Category (think folder) and this category may have lots of sub categories and each of the sub categories could have 1000 of media containers (think file reference objects) which contain information about a file that may be on a NAS or SAN server (files are videos in this case). The relationship between these categories is stored in a database together with some permission rules and meta data about the sub categories. So from a UI perspective we have a lazy loaded tree control which is driven by the user by clicking on each sub folder (think of Windows explorer). Once they come to a URL of the video file, they then can watch the video. The number of users could grow into the 1000s and the sub categories and videos could be in the 10000s as the system grows. The question is should we carry on the way it is currently working where each request hits the database or should we think about caching the data? We are on using IIS 6/7 and Asp.net.

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  • Is it bad practice to make an iterator that is aware of its own end

    - by aaronman
    For some background of why I am asking this question here is an example. In python the method chain chains an arbitrary number of ranges together and makes them into one without making copies. Here is a link in case you don't understand it. I decided I would implement chain in c++ using variadic templates. As far as I can tell the only way to make an iterator for chain that will successfully go to the next container is for each iterator to to know about the end of the container (I thought of a sort of hack in where when != is called against the end it will know to go to the next container, but the first way seemed easier and safer and more versatile). My question is if there is anything inherently wrong with an iterator knowing about its own end, my code is in c++ but this can be language agnostic since many languages have iterators. #ifndef CHAIN_HPP #define CHAIN_HPP #include "iterator_range.hpp" namespace iter { template <typename ... Containers> struct chain_iter; template <typename Container> struct chain_iter<Container> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end;//never really used but kept it for consistency public: chain_iter(Container & container, bool is_end=false) : begin(container.begin()),end(container.end()) { if(is_end) begin = container.end(); } chain_iter & operator++() { ++begin; return *this; } auto operator*()->decltype(*begin) { return *begin; } bool operator!=(const chain_iter & rhs) const{ return this->begin != rhs.begin; } }; template <typename Container, typename ... Containers> struct chain_iter<Container,Containers...> { private: using Iterator = decltype(((Container*)nullptr)->begin()); Iterator begin; const Iterator end; bool end_reached = false; chain_iter<Containers...> next_iter; public: chain_iter(Container & container, Containers& ... rest, bool is_end=false) : begin(container.begin()), end(container.end()), next_iter(rest...,is_end) { if(is_end) begin = container.end(); } chain_iter & operator++() { if (begin == end) { ++next_iter; } else { ++begin; } return *this; } auto operator*()->decltype(*begin) { if (begin == end) { return *next_iter; } else { return *begin; } } bool operator !=(const chain_iter & rhs) const { if (begin == end) { return this->next_iter != rhs.next_iter; } else return this->begin != rhs.begin; } }; template <typename ... Containers> iterator_range<chain_iter<Containers...>> chain(Containers& ... containers) { auto begin = chain_iter<Containers...>(containers...); auto end = chain_iter<Containers...>(containers...,true); return iterator_range<chain_iter<Containers...>>(begin,end); } } #endif //CHAIN_HPP

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  • Should I use an interface when methods are only similar?

    - by Joshua Harris
    I was posed with the idea of creating an object that checks if a point will collide with a line: public class PointAndLineSegmentCollisionDetector { public void Collides(Point p, LineSegment s) { // ... } } This made me think that if I decided to create a Box object, then I would need a PointAndBoxCollisionDetector and a LineSegmentAndBoxCollisionDetector. I might even realize that I should have a BoxAndBoxCollisionDetector and a LineSegmentAndLineSegmentCollisionDetector. And, when I add new objects that can collide I would need to add even more of these. But, they all have a Collides method, so everything I learned about abstraction is telling me, "Make an interface." public interface CollisionDetector { public void Collides(Spatial s1, Spatial s2); } But now I have a function that only detects some abstract class or interface that is used by Point, LineSegment, Box, etc.. So if I did this then each implementation would have to to a type check to make sure that the types are the appropriate type because the collision algorithm is different for each different type match up. Another solution could be this: public class CollisionDetector { public void Collides(Point p, LineSegment s) { ... } public void Collides(LineSegment s, Box b) { ... } public void Collides(Point p, Box b) { ... } // ... } But, this could end up being a huge class that seems unwieldy, although it would have simplicity in that it is only a bunch of Collide methods. This is similar to C#'s Convert class. Which is nice because it is large, but it is simple to understand how it works. This seems to be the better solution, but I thought I should open it for discussion as a wiki to get other opinions.

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  • How do we know to favour composition over generalisation is always the right choice?

    - by Carnotaurus
    Whether an object physically exists or not, we can choose to model it in different ways. We could arbitarily use generalisation or composition in many cases. However, the GoF principle of "favour composition over generalisation [sic]" guides us to use composition. So, when we model, for example, a line then we create a class that contains two members PointA and PointB of the type Point (composition) instead of extending Point (generalisation). This is just a simplified example of how we can arbitarily choose composition or inheritance to model, despite that objects are usually much more complex. How do we know that this is the right choice? It matters at least because there could be a ton of refactoring to do if it is wrong?

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  • Trying to find a recent - PHP book - that utilizes SOLID principles! [closed]

    - by darga33
    Pulling my hair out! I have heard of Martin Fowler's book PoEAA and the other book Head First OOA OOD but those are not in PHP. I desperately want to read them, but ONLY in PHP utilizing the - SOLID acronym - principles! Does anyone know of the absolute best, most recent PHP book that utilizes the SOLID principles and GRASP, and all the other best practices? I want to learn from the best possible source! Not beginner books! I already understand OOP. This seems like an almost impossible question to find the answer to and so I thought, hey, might as well post on stackexchange!! Surely someone out there must know!!!!!!!!!! Or if noone happens to know, Maybe they know of an open source application that utilizes these principles that is relatively small that is not a framework. Something that I can go through every single class, and spend time understanding the insides and outs of how the program was developed. Thanks so much in advance! I really really really really appreciate it! Well it looks like we aren't supposed to ask about best books, so nevermind this question! Sorry about that!

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  • What should a game have in order to keep humans playing it?

    - by Adam Davis
    In many entertainment professions there suggestions, loose rules, or general frameworks one follows that appeal to humans in one way or another. For instance, many movies and books follow the monomyth. In video games I find many types of games that attract people in different ways. Some are addicted to facebook gem matching games. Others can't get enough of FPS games. Once in awhile, though, you find a game that seems to transcend stereotypes and appeals almost immediately to everyone that plays it. For instance, Plants Versus Zombies seems to have a very, very large demographic of players. There are other games similar in reach. I'm curious what books, blogs, etc there are that explore these game types and styles, and tries to suss out one or more popular frameworks/styles that satisfy people, while keeping them coming back for more.

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  • Methods of ordering function definitions in code

    - by xralf
    When I work on some programming project (usually command line application in Python with many switches), I'm usually creating about 30 and more functions. Most of the functions are in one file (except some helpers that I utilize in more projects). Some of the functions are called on particular switch (like -p or --print) but many functions do some helper computations, print operations or database operations because I don't want to main functions be too large. When I have an idea for a new functionality I often put new functions randomly to the file. Should I think more about it and place it to some particular place? Are there some methods for this?

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  • Is game development Subcontracted?

    - by Darv
    I was having a conversation with someone who believed that components of a games code where subcontracted out to programmers in different countries where it would be cheaper, then assembled by the local company. I understand that people often use pre-built engines but I would think that making the actual game would require people to work closely in the same studio. I couldn't find much clear information on this when I looked, does anyone know?

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