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• How to program for constraints/rules

  - by Gaurav

  First the background, during interviews in the past, many times I have been asked to design some or other variation of card game as programming puzzle, and I have tried to design it in OO way, but I have never been satisfied with my solutions. However it was not until recently that I realized that I had been approaching the problem from the wrong direction. Specifically I was trying to solve the problem by modeling individual card as an object. Problem with this is individual cards don't have any non-trivial intrinsic behavior and therefore are not suitable (or primary) candidate as objects. What is interesting and important about cards are rules and constraints, such as there could be only four suits, or only thirteen cards in each suit. Of course, then there are any number of rules for games. So my questions are Are there any idioms/constructs/patterns to program for rules & constraints. How many in 1 can be applied in conjunction with OO paradigm.

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• Formal definition for term "pure OO language"?

  - by Yauhen Yakimovich

  I can't think of a better place among SO siblings to pose such a question. Originally I wanted to ask "Is python a pure OO language?" but considering troubles and some sort of discomfort people experience while trying to define the term I decided to start with obtaining a clear definition for the term itself. It would be rather fair to start with correspondence by Dr. Alan Kay, who has coined the term (note the inspiration in biological analogy to cells or other living objects). There are following ways to approach the task: Give a comparative analysis by listing programming languages that exhibits certain properties unique and sufficient to define the term (although Smalltalk and Java are passing examples but IMO this way seems neither really complete or nor fruitful) Give a formal definition (or close to it, e.g. in more academic or mathematical style). Give a philosophical definition that would totally rely on semantical context of concrete language or a priori programming experience (there must be some chance of successful explanation by the community). My current version: "If a certain programing (formal) language that can (grammatically) differentiate between operations and operands as well as infer about the type of each operand whether this type is an object (in sense of OOP) or not then we call such a language an OO-language as long as there is at least one type in this language which is an object. Finally, if all types of the language are also objects we define such language to be pure OO-language." Would appreciate any possible improvement of it. As you can see I just made the definition dependent on the term "object" (often fully referenced as class of objects).

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• Whole map design vs. tiles array design

  - by Mikalichov

  I am working on a 2D RPG, which will feature the usual dungeon/town maps (pre-generated). I am using tiles, that I will then combine to make the maps. My original plan was to assemble the tiles using Photoshop, or some other graphic program, in order to have one bigger picture that I could then use as a map. However, I have read on several places people talking about how they used arrays to build their map in the engine (so you give an array of x tiles to your engine, and it assemble them as a map). I can understand how it's done, but it seems a lot more complicated to implement, and I can't see obvious avantages. What is the most common method, and what are advantages/disadvantages of each?

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• Better Understand the 'Strategy' Design Pattern

  - by Imran Omar Bukhsh

  Greetings Hope you all are doing great. I have been interested in design patterns for a while and started reading 'Head First Design Patterns'. I started with the first pattern called the 'Strategy' pattern. I went through the problem outlined in the images below and first tried to propose a solution myself so I could really grasp the importance of the pattern. So my question is that why is my solution ( below ) to the problem outlined in the images below not good enough. What are the good / bad points of my solution vs the pattern? What makes the pattern clearly the only viable solution ? Thanks for you input, hope it will help me better understand the pattern. MY SOLUTION Parent Class: DUCK <?php class Duck { public $swimmable; public $quackable; public $flyable; function display() { echo "A Duck Looks Like This<BR/>"; } function quack() { if($this->quackable==1) { echo("Quack<BR/>"); } } function swim() { if($this->swimmable==1) { echo("Swim<BR/>"); } } function fly() { if($this->flyable==1) { echo("Fly<BR/>"); } } } ?> INHERITING CLASS: MallardDuck <?php class MallardDuck extends Duck { function MallardDuck() { $this->quackable = 1; $this->swimmable = 1; } function display() { echo "A Mallard Duck Looks Like This<BR/>"; } } ?> INHERITING CLASS: WoddenDecoyDuck <?php class WoddenDecoyDuck extends Duck { function woddendecoyduck() { $this->quackable = 0; $this->swimmable = 0; } function display() { echo "A Wooden Decoy Duck Looks Like This<BR/>"; } } Thanking you for your input. Imran

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• Game software design

  - by L. De Leo

  I have been working on a simple implementation of a card game in object oriented Python/HTML/Javascript and building on the top of Django. At this point the game is in its final stage of development but, while spotting a big issue about how I was keeping the application state (basically using a global variable), I reached the point that I'm stuck. The thing is that ignoring the design flaw, in a single-threaded environment such as under the Django development server, the game works perfectly. While I tried to design classes cleanly and keep methods short I now have in front of me an issue that has been keeping me busy for the last 2 days and that countless print statements and visual debugging hasn't helped me spot. The reason I think has to do with some side-effects of functions and to solve it I've been wondering if maybe refactoring the code entirely with static classes that keep no state and just passing the state around might be a good option to keep side-effects under control. Or maybe trying to program it in a functional programming style (although I'm not sure Python allows for a purely functional style). I feel that now there's already too many layers that the software (which I plan to make incredibly more complex by adding non trivial features) has already become unmanageable. How would you suggest I re-take control of my code-base that (despite being still only at < 1000 LOC) seems to have taken a life of its own?

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• How far to go with Domain Driven Design?

  - by synti

  I've read a little about domain driven design and the usage of a rich domain model, as described by Martin Fowler, and I've decided to put it in practice in a personal project, instead of using transaction scripts. Everything went fine until UI implementation started. The thing is some views will use rich components that are backed up by unusual models and, thus, I must transform the domain model into what is used by those components. And that transformation is specially "complex" in the view-to-domain portion, up to the point that some business logic is involved. Wich brings me to the questioning: where should I do these adaptations? So far I've got the following conclusions: Doing it in the presentation layer is good because, well, if that layer imposes restrictions in it's model, then it should be the one to handle them. But it's bad because there'll be some business leakage. If I do it on the services objects (controllers, actions, whatever), then it'd be good because there won't be any change to the domain API just because of presentation layer, but it's bad because then I'd have transaction scripts, wich is not the intended design. Finally, if I do it on the domain model, there'd be no leakage of business logic at all. But in the future I could expect an explosion of the API into a series of methods designed just to handle that view-model <- domain-model adaptation. I hope I could make myself clear on this.

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• DDD Model Design and Repository Persistence Performance Considerations

  - by agarhy

  So I have been reading about DDD for some time and trying to figure out the best approach on several issues. I tend to agree that I should design my model in a persistent agnostic manner. And that repositories should load and persist my models in valid states. But are these approaches realistic practically? I mean its normal for a model to hold a reference to a collection of another type. Persisting that model should mean persist the entire collection. Fine. But do I really need to load the entire collection every time I load the model? Probably not. So I can have specialized repositories. Some that load maybe a subset of the object graph via DTOs and others that load the entire object graph. But when do I use which? If I have DTOs, what's stopping client code from directly calling them and completely bypassing the model? I can have mappers and factories to create my models from DTOs maybe? But depending on the design of my models that might not always work. Or it might not allow my models to be created in a valid state. What's the correct approach here?

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• Architecture design with MyBatis mappers

  - by Wolf

  I am creating rest web service for providing data. I am using Spring MVC for handling rest requests, and MyBatis for data access. Application should be designed in the way that it should be easy to change the data access implementation (for example to hibernate or something else) and it has to be fast (so I am trying to avoid unnecessary overcomplication of design). Now my question is about the general design of layers. I would normally use DAO interface and then different implementations for different data access strategies, but MyBatis uses interfaces to access the data. So I can think of 2 possible models but I am not sure which one is better or if there is any other nice way: Controller layer - uses Service layer interfaces services are then implemented for each data access stretegy - for example for mybatis: service implementation uses Mapper classes to access data and do whatever it needs to do with them and sends them to controller layer Controller layer - uses Service layer - service layer uses DAO interfaces DAOs are then implemented for each data access strategy - for example for mybatis: DAO class uses mapper interface to access data and sends them to service layer, service layer then do whatever it needs to do with them and sends them to controller layer I prefer the first strategy as it seems to be less complicated, but then I would have to write all of the service code for another data access again. What do you think? Thank You

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• 5 Design Tricks Facebook Uses To Affect Your Privacy Decisions

  - by Jason Fitzpatrick

  If you feel like Facebook increasingly has fewer and fewer options to reject applications and organization access to your private information, you’re not imagining it. Here are five ways Facebook’s design choices in the App Center have minimized your choices over time. Over at TechCrunch they have a guest post by Avi Charkham highlighting five ways recent changes to the Facebook App Center put privacy settings on the back burner. In regard to the comparison seen in the image above, for example, he writes: #1: The Single Button Trick In the old design Facebook used two buttons – “Allow” and “Don’t Allow” – which automatically led you to make a decision. In the new App Center Facebook chose to use a single button. No confirmation, no decisions to make. One click and, boom, your done! Your information was passed on to the app developers and you never even notice it. Hit up the link below to check out the other four redesign choices that minimize the information about privacy and data usage you see and maximize the click-through and acceptance rate for apps. How To Switch Webmail Providers Without Losing All Your Email How To Force Windows Applications to Use a Specific CPU HTG Explains: Is UPnP a Security Risk?

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• Example of DOD design (on a generic Zombie game)

  - by Jeffrey

  I can't seem to find a nice explanation of the Data Oriented Design for a generic zombie game (it's just an example, pretty common example). Could you make an example of the Data Oriented Design on creating a generic zombie class? Is the following good? Zombie list class: class ZombieList { GLuint vbo; // generic zombie vertex model std::vector<color>; // object default color std::vector<texture>; // objects textures std::vector<vector3D>; // objects positions public: unsigned int create(); // return object id void move(unsigned int objId, vector3D offset); void rotate(unsigned int objId, float angle); void setColor(unsigned int objId, color c); void setPosition(unsigned int objId, color c); void setTexture(unsigned int, unsigned int); ... void update(Player*); // move towards player, attack if near } Example: Player p; Zombielist zl; unsigned int first = zl.create(); zl.setPosition(first, vector3D(50, 50)); zl.setTexture(first, texture("zombie1.png")); ... while (running) { // main loop ... zl.update(&p); zl.draw(); // draw every zombie } Or would creating a generic World container that contains every action from bite(zombieId, playerId) to moveTo(playerId, vector) to createPlayer() to shoot(playerId, vector) to face(radians)/face(vector); and contains: std::vector<zombie> std::vector<player> ... std::vector<mapchunk> ... std::vector<vbobufferid> player_run_animation; ... be a good example? Whats the proper way to organize a game with DOD?

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• Design pattern for client/server sessions?

  - by nonot1

  Are there any common patterns or general guidance I can learn from for how to design a client/server system where the both the client and server must maintain some kind per-client session state? I've found any number of libraries that can help with some of the plumbing, but it's the overall design I'm wondering about. Open issues in my mind: How to structure the client/server communication so that bidirectional synchronous and asynchronous requests are possible? The server side needs to spawn a couple of per-connected-client session-long helper process. How to manage that? How to manage the mapping from a given client (and any of it's requests) to server state and helper process instances in the face of multiple clients and intermittent network connectivity. Most communication can be simple blocking request/reply, but some will be long running processing tasks that the client will want to keep tabs on. To the extent that it matters, the platform is Linux/C/C++. Not web based. Just an existing thick-client software app being modified to talk to backend servers for some tasks.

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• Class Design for special business rules

  - by Samuel Front

  I'm developing an application that allows people to place custom manufacturing orders. However, while most require similar paperwork, some of them have custom paperwork that only they require. My current class design has a Manufacturer class, of which of one of the member variables is an array of RequiredSubmission objects. However, there are two issues that I am somewhat concerned about. First, some manufacturers are willing to accept either a standard form or their own custom form. I'm thinking of storing this in the RequiredSubmission object, with an array of alternate forms that are a valid substitute. I'm not sure that this is ideal, however. The major issue, however, is that some manufacturers have deadline cycles. For example, forms A, B and C have to be delivered by January 1, while payment must be rendered by January 10. If you miss those, you'll have to wait until the next cycle. I'm not exactly sure how I can get this to work with my existing classes—how can I say "this set of dates all belong to the same cycle, with date A for form A, date B for form B, etc." I would greatly appreciate any insights on how to best design these classes.

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• KISS principle applied to programming language design?

  - by Giorgio

  KISS ("keep it simple stupid", see e.g. here) is an important principle in software development, even though it apparently originated in engineering. Citing from the wikipedia article: The principle is best exemplified by the story of Johnson handing a team of design engineers a handful of tools, with the challenge that the jet aircraft they were designing must be repairable by an average mechanic in the field under combat conditions with only these tools. Hence, the 'stupid' refers to the relationship between the way things break and the sophistication available to fix them. If I wanted to apply this to the field of software development I would replace "jet aircraft" with "piece of software", "average mechanic" with "average developer" and "under combat conditions" with "under the expected software development / maintenance conditions" (deadlines, time constraints, meetings / interruptions, available tools, and so on). So it is a commonly accepted idea that one should try to keep a piece of software simple stupid so that it easy to work on it later. But can the KISS principle be applied also to programming language design? Do you know of any programming languages that have been designed specifically with this principle in mind, i.e. to "allow an average programmer under average working conditions to write and maintain as much code as possible with the least cognitive effort"? If you cite any specific language it would be great if you could add a link to some document in which this intent is clearly expressed by the language designers. In any case, I would be interested to learn about the designers' (documented) intentions rather than your personal opinion about a particular programming language.

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• How to visualize the design of a program in order to communicate it to others

  - by Joris Meys

  I am (re-)designing some packages for R, and I am currently working out the necessary functions, objects, both internal and for the interface with the user. I have documented the individual functions and objects. So I have the description of all the little parts. Now I need to give an overview of how the parts fit together. The scheme of the motor so to say. I've started with making some flowchart-like graphs in Visio, but that quickly became a clumsy and useless collection of boxes, arrrows and-what-not. So hence the question: Is there specific software you can use for vizualizing the design of your program If so, care to share some tips on how to do this most efficiently If not, how do other designers create the scheme of their programs and communicate that to others? Edit: I am NOT asking how to explain complex processes to somebody, nor asking how to illustrate programming logic. I am asking how to communicate the design of a program/package, i.e.: the objects (with key features and representation if possible) the related functions (with arguments and function if possible) the interrelation between the functions at the interface and the internal functions (I'm talking about an extension package for a scripting language, keep that in mind) So something like this : But better. This is (part of) the interrelations between functions in the old package that I'm now redesigning for obvious reasons :-) PS : I made that graph myself, using code extraction tools on the source and feeding the interrelation matrix to yEd Graph Editor.

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• Data classes: getters and setters or different method design

  - by Frog

  I've been trying to design an interface for a data class I'm writing. This class stores styles for characters, for example whether the character is bold, italic or underlined. But also the font-size and the font-family. So it has different types of member variables. The easiest way to implement this would be to add getters and setters for every member variable, but this just feels wrong to me. It feels way more logical (and more OOP) to call style.format(BOLD, true) instead of style.setBold(true). So to use logical methods insteads of getters/setters. But I am facing two problems while implementing these methods: I would need a big switch statement with all member variables, since you can't access a variable by the contents of a string in C++. Moreover, you can't overload by return type, which means you can't write one getter like style.getFormatting(BOLD) (I know there are some tricks to do this, but these don't allow for parameters, which I would obviously need). However, if I would implement getters and setters, there are also issues. I would have to duplicate quite some code because styles can also have a parent styles, which means the getters have to look not only at the member variables of this style, but also at the variables of the parent styles. Because I wasn't able to figure out how to do this, I decided to ask a question a couple of weeks ago. See Object Oriented Programming: getters/setters or logical names. But in that question I didn't stress it would be just a data object and that I'm not making a text rendering engine, which was the reason one of the people that answered suggested I ask another question while making that clear (because his solution, the decorator pattern, isn't suitable for my problem). So please note that I'm not creating my own text rendering engine, I just use these classes to store data. Because I still haven't been able to find a solution to this problem I'd like to ask this question again: how would you design a styles class like this? And why would you do that? Thanks on forehand!

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• Putting Together a Game Design Team?

  - by Kaia

  I'm attempting to put together a game design team that is willing to help me design/program, test, and somewhat produce the game we make to the public. I need anyone who knows anything about programming/coding, designing, etc. Once we get it up and running and out into the world (over dramatic maybe? haha) I have ideas of generating a profit from it so there is a possibility of payment. My thinking on it (so far) is this: 2D (possibly. I haven't decided if I want it 2D or 3D. It really depends on what is easier) 3rd person. Adventure (I want there to be a point to it, but like a point with no real end) I want there to be a story to it. If you've ever played Dofus, think like that. There is a story to the game, but no real end. I want (if possible) to include mini-games. These could end up becoming a possible way for a player to aquire in-game money, quest items, etc. If anyone is interested in helping me create the story line/script (which we will finsih first, before creating the game) please contact me. I want to get this completed as soon as possible.

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• How to effectively design a piece of software

  - by ti83plus

  Im a compsci student and ive got some experience in various languages and paradigms c/java/python/ruby/html/css/scheme/sql/asp(classic). I realise that i want to have some software in my portfolio for future job hunting even tho i still have 2 years left of my education. Ive got a pretty good idea of what i want to make, its a webapp. Most shops around here are either .net or java and since i know java best and dont have access to ms developer tools im thinking i should go with java. Even tho i feel i know the principles of OOP pretty good ive got no clue how to go from my idea to a working solution. Where can i access information about designing the underlying architechture of my solution? Also i would like to know what other technologies i should train on, my current list includes javascript(and possibly a javascript library) some sort of java web framework tips are appreciated. I would like to add support for android/iphone apps in the future and this is something i have to take into account when designing the app. I have done a course on software engineering but i found this to be more centered around project management ideas then the actual design and implementation. So i would like tips on technologies i should focus on to get the most out of my time without the massive overhead of huge config processes but at the same time keep my project viable in a business sense, so that i use technologies that are relevant for business (java developer jobs). And i would also like tips on where i can learn more about the design process around a software project, i will be working mostly alone. But i find the approach ive used up until now (start coding and figure it out as you go) wont suffice.

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• Example of DOD design

  - by Jeffrey

  I can't seem to find a nice explanation of the Data Oriented Design for a generic zombie game (it's just an example, pretty common example). Could you make an example of the Data Oriented Design on creating a generic zombie class? Is the following good? Zombie list class: class ZombieList { GLuint vbo; // generic zombie vertex model std::vector<color>; // object default color std::vector<texture>; // objects textures std::vector<vector3D>; // objects positions public: unsigned int create(); // return object id void move(unsigned int objId, vector3D offset); void rotate(unsigned int objId, float angle); void setColor(unsigned int objId, color c); void setPosition(unsigned int objId, color c); void setTexture(unsigned int, unsigned int); ... void update(Player*); // move towards player, attack if near } Example: Player p; Zombielist zl; unsigned int first = zl.create(); zl.setPosition(first, vector3D(50, 50)); zl.setTexture(first, texture("zombie1.png")); ... while (running) { // main loop ... zl.update(&p); zl.draw(); // draw every zombie } Or would creating a generic World container that contains every action from bite(zombieId, playerId) to moveTo(playerId, vector) to createPlayer() to shoot(playerId, vector) to face(radians)/face(vector); and contains: std::vector<zombie> std::vector<player> ... std::vector<mapchunk> ... std::vector<vbobufferid> player_run_animation; ... be a good example? Whats the proper way to organize a game with DOD?

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• Good design for class with similar constructors

  - by RustyTheBoyRobot

  I was reading this question and thought that good points were made, but most of the solutions involved renaming one of the methods. I am refactoring some poorly written code and I've run into this situation: public class Entity { public Entity(String uniqueIdentifier, boolean isSerialNumber) { if (isSerialNumber) { this.serialNumber = uniqueIdentifier; //Lookup other data } else { this.primaryKey = uniqueIdentifier; // Lookup other data with different query } } } The obvious design flaw is that someone needed two different ways to create the object, but couldn't overload the constructor since both identifiers were of the same type (String). Thus they added a flag to differentiate. So, my question is this: when this situation arises, what are good designs for differentiating between these two ways of instantiating an object? My First Thoughts You could create two different static methods to create your object. The method names could be different. This is weak because static methods don't get inherited. You could create different objects to force the types to be different (i.e., make a PrimaryKey class and a SerialNumber class). I like this because it seems to be a better design, but it also is a pain to refactor if serialNumber is a String everywhere else.

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• Design Pattern for Skipping Steps in a Wizard

  - by Eric J.

  I'm designing a flexible Wizard system that presents a number of screens to complete a task. Some screens may need to be skipped based on answers to prompts on one or more previous screens. The conditions to skip a given screen need to be editable by a non-technical user via a UI. Multiple conditions need only be combined with and. I have an initial design in mind, but it feels inelegant. I wonder if there's a better way to approach this class of problem. Initial Design UI where The first column allows the user to select a question from a previous screen. The second column allows the user to select an operator applicable to the type of question asked. The third column allows the user to enter one or more values depending on the selected operator. Object Model public enum Operations { ... } public class Condition { int QuestionId { get; set; } Operations Operation { get; set; } List<object> Parameters { get; private set; } } List<Condition> pageSkipConditions; Controller Logic bool allConditionsTrue = pageSkipConditions.Count > 0; foreach (Condition c in pageSkipConditions) { allConditionsTrue &= Evaluate(previousAnswers, c); } // ... private bool Evaluate(List<Answers> previousAnswers, Condition c) { switch (c.Operation) { case Operations.StartsWith: // logic for this operation // etc. } }

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• REST API wrapper - class design for 'lite' object responses

  - by sasfrog

  I am writing a class library to serve as a managed .NET wrapper over a REST API. I'm very new to OOP, and this task is an ideal opportunity for me to learn some OOP concepts in a real-life situation that makes sense to me. Some of the key resources/objects that the API returns are returned with different levels of detail depending on whether the request is for a single instance, a list, or part of a "search all resources" response. This is obviously a good design for the REST API itself, so that full objects aren't returned (thus increasing the size of the response and therefore the time taken to respond) unless they're needed. So, to be clear: .../car/1234.json returns the full Car object for 1234, all its properties like colour, make, model, year, engine_size, etc. Let's call this full. .../cars.json returns a list of Car objects, but only with a subset of the properties returned by .../car/1234.json. Let's call this lite. ...search.json returns, among other things, a list of car objects, but with minimal properties (only ID, make and model). Let's call this lite-lite. I want to know what the pros and cons of each of the following possible designs are, and whether there is a better design that I haven't covered: Create a Car class that models the lite-lite properties, and then have each of the more detailed responses inherit and extend this class. Create separate CarFull, CarLite and CarLiteLite classes corresponding to each of the responses. Create a single Car class that contains (nullable?) properties for the full response, and create constructors for each of the responses which populate it to the extent possible (and maybe include a property that returns the response type from which the instance was created). I expect among other things there will be use cases for consumers of the wrapper where they will want to iterate through lists of Cars, regardless of which response type they were created from, such that the three response types can contribute to the same list. Happy to be pointed to good resources on this sort of thing, and/or even told the name of the concept I'm describing so I can better target my research.

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• Are ORM's counterproductive to OO design?

  - by Jeremiah

  In OOD, design of an object is said to be characterized by its identity and behavior. Having used OR/M's in the past, the primary purpose, in my opinion, revolves around the ability to store/retrieve data. That is to say, OR/M objects are not design by behavior, but rather data (i.e. database tables). Case and point: Many OR/M tools come with a point-to-a-database-table-and-click-object-generator. If objects are no longer characterized by behavior this will, in my opinion, muddy the identity and responsibility of the objects. Subsequently, if objects are not defined by a responsibility this could lend a hand to having tightly coupled classes and overall poor design. Furthermore, I would think that in an application setting, you would be heading towards scalability issues. So, my question is, do you think that ORM's are counterproductive to OO design? Perhaps the underlying question would be whether or not they are counterproductive to application development.

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• Design suggestion for expression tree evaluation with time-series data

  - by Lirik

  I have a (C#) genetic program that uses financial time-series data and it's currently working but I want to re-design the architecture to be more robust. My main goals are: sequentially present the time-series data to the expression trees. allow expression trees to access previous data rows when needed. to optimize performance of the data access while evaluating the expression trees. keep a common interface so various types of data can be used. Here are the possible approaches I've thought about: I can evaluate the expression tree by passing in a data row into the root node and let each child node use the same data row. I can evaluate the expression tree by passing in the data row index and letting each node get the data row from a shared DataSet (currently I'm passing the row index and going to multiple synchronized arrays to get the data). Hybrid: an immutable data set is accessible by all of the expression trees and each expression tree is evaluated by passing in a data row. The benefit of the first approach is that the data row is being passed into the expression tree and there is no further query done on the data set (which should increase performance in a multithreaded environment). The drawback is that the expression tree does not have access to the rest of the data (in case some of the functions need to do calculations using previous data rows). The benefit of the second approach is that the expression trees can access any data up to the latest data row, but unless I specify what that row is, I'll have to iterate through the rows and figure out which one is the last one. The benefit of the hybrid is that it should generally perform better and still provide access to the earlier data. It supports two basic "views" of data: the latest row and the previous rows. Do you guys know of any design patterns or do you have any tips that can help me build this type of system? Should I use a DataSet to hold and present the data, or are there more efficient ways to present rows of data while maintaining a simple interface? FYI: All of my code is written in C#.

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• 'Forward-Compatible' Program Design

  - by Jeffrey Kern

  The majority of my questions I've asked here so far on StackOverflow have been how to implement individual concepts and techniques towards developing a software-based NES clone via the XNA environment. The small samples that I've thrown together on my PC work relatively great and everything. Except I hit a brick wall. How do I merge all of these samples together. Having proof-of-concept is amazing, except when you need it to go beyond just that. I now have samples strewn about that I'm trying to merge, some of them incomplete. And now I'm stuck with the chicken-and-the-egg situation of where I would like to incorporate these samples together, to make sure they work, but I cannot without test data. And I don't have tools to create test data, because they'd need to be based off of the individual pieces that need to be put together. In my mind, I'm having nightmares with circular reference. For my sample data, I am hoping to save it in XML and write a specification - and then make sample data by hand - but I'm too paranoid of manually creating an XML file full of incorrect data and blaming it on my code, or vice-versa. It doesn't help that the end-result of my work is graphic-oriented, which makes it interseting how a graphic on the screen can be visualized in XML Nodes. I guess, my question is this: What design patterns and disciplines exist in the coding world that address this type of concern? I've always relied on brute-force coding and restarting a project with a whole new code base in attempts to further along my goals, but I doubt that would be the best way to do so. Within my college career, the majority of my programming was to work on simple projects that came out of a book, or with a given correct data set and a verifyable result. I don't have that, as my own design documents that I am going by could be terribly wrong.

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• Design for a Debate club assignment application

  - by Amir Rachum

  Hi all, For my university's debate club, I was asked to create an application to assign debate sessions and I'm having some difficulties as to come up with a good design for it. I will do it in Java. Here's what's needed: What you need to know about BP debates: There are four teams of 2 debaters each and a judge. The four groups are assigned a specific position: gov1, gov2, op1, op2. There is no significance to the order within a team. The goal of the application is to get as input the debaters who are present (for example, if there are 20 people, we will hold 2 debates) and assign them to teams and roles with regards to the history of each debater so that: Each debater should debate with (be on the same team) as many people as possible. Each debater should uniformly debate in different positions. The debate should be fair - debaters have different levels of experience and this should be as even as possible - i.e., there shouldn't be a team of two very experienced debaters and a team of junior debaters. There should be an option for the user to restrict the assignment in various ways, such as: Specifying that two people should debate together, in a specific position or not. Specifying that a single debater should be in a specific position, regardless of the partner. etc... If anyone can try to give me some pointers for a design for this application, I'll be so thankful! Also, I've never implemented a GUI before, so I'd appreciate some pointers on that as well, but it's not the major issue right now.

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