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• Implementing MVC pattern in SWT application

  - by Pradeep Simha

  I am developing an SWT application (it's basically an Eclipse plugin, so I need to use SWT). Currently my design is as follows: Model: In model, I have POJOs which represents the actual fields in views. View: It is a dumb layer, it contains just UI and contains no logic (not even event handlers) Controller: It acts as a mediator b/w those two layers. Also it is responsible for creating view layer, handling events etc. Basically I have created all of the controls in view as a static like this public static Button btnLogin and in controller I have a code like this: public void createLoginView(Composite comp) { LoginFormView.createView(comp); //This createView method is in view layer ie LoginFormView LoginFormView.btnLogin.addSelectionListener(new SelectionListener() { //Code goes here }); } Similalrly I have done for other views and controls. So that in main class and other classes I am calling just createLoginView of controller. I am doing similar thing for other views. So my question, is what I am doing is correct? Is this design good? Or I should have followed any other approach. Since I am new to SWT and Eclipse plugin development (basically I am Java EE developer having 4+ years of exp). Any tips/pointers would be appreciated.

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• How to Be a Software Engineer?

  - by Mistrio

  My problem is kind of weird so please bear with me. I have been working in a start up concerned basically with mobile development since my graduation 2 years ago. I develop apps for iOS but it's not really relevant. The start up structure is simply founders developers, with no middle-tier technical supervision or project management whatsoever. A typical project cycle of ours is like this: meet with a client send very vague recruitment to an outsourced graphics designer dig in development right after we get the design, no questions asked then improvise improvise improvise! It's not that we are unaware that stuff like requirements analysis, UML, design patterns, source code control, testing, development methodologies... etc. exist, we just simply don't use them, and I mean like never. The result is usually a clunk of hardly-maintainable yet working code. Despite everything we are literally flourishing with many successful apps on all platforms and bigger clients each project. The thing is, we want the chaos and we're looking for advice. How would you fix our company technically? Given that you can't hire project managers or team leaders just because we are barely 5 developers, so it wouldn't be a justified cost for the founders, but one-time things like courses, books, private training... etc is an option. Lastly, if it's relevant, we are based in Egypt. Thank you a lot in advance.

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• Simple Multiplayer CCG System

  - by TobiHeidi

  I am working on a cross plattform Multiplayer CCG (web, android, ios). Here are my goals in design: I want to game to be easly accessible and understandable for non CCG players within the first minute of play. a single game should be played by 2 - 4 players a once, without problems if one players drops out during play. players should make their next turn simultaneous (without waiting for other to make their turns) My current approach: each Card has a point value for four Elements. In each Turn an Element is (randomly) selected and every Player chooses 1 card out of 3. The Player choosen the card with the highest value for that element wins the Round. After 10 Rounds the players a ranked by how many rounds they won. Why does this approach seems not optimal? It seems really to easy to determin the next best turn. Your own turn is to little affected by the play style of the others. I would love the have a system where some cards are better against other cards. A bit of rock paper scissors where you have to think about what next turn the other players will make or so. But really think freely. I would love to hear ideas may it be additions or new systems to make a CCG with roughly the stated design goals. Thanks

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• Should one always know what an API is doing just by looking at the code?

  - by markmnl

  Recently I have been developing my own API and with that invested interest in API design I have been keenly interested how I can improve my API design. One aspect that has come up a couple times is (not by users of my API but in my observing discussion about the topic): one should know just by looking at the code calling the API what it is doing. For example see this discussion on GitHub for the discourse repo, it goes something like: foo.update_pinned(true, true); Just by looking at the code (without knowing the parameter names, documentation etc.) one cannot guess what it is going to do - what does the 2nd argument mean? The suggested improvement is to have something like: foo.pin() foo.unpin() foo.pin_globally() And that clears things up (the 2nd arg was whether to pin foo globally, I am guessing), and I agree in this case the later would certainly be an improvement. However I believe there can be instances where methods to set different but logically related state would be better exposed as one method call rather than separate ones, even though you would not know what it is doing just by looking at the code. (So you would have to resort to looking at the parameter names and documentation to find out - which personally I would always do no matter what if I am unfamiliar with an API). For example I expose one method SetVisibility(bool, string, bool) on a FalconPeer and I acknowledge just looking at the line: falconPeer.SetVisibility(true, "aerw3", true); You would have no idea what it is doing. It is setting 3 different values that control the "visibility" of the falconPeer in the logical sense: accept join requests, only with password and reply to discovery requests. Splitting this out into 3 method calls could lead to a user of the API to set one aspect of "visibility" forgetting to set others that I force them to think about by only exposing the one method to set all aspects of "visibility". Furthermore when the user wants to change one aspect they almost always will want to change another aspect and can now do so in one call.

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• Implementing game rules in a tactical battle board game

  - by Setzer22

  I'm trying to create a game similar to what one would find in a typical D&D board game combat. For mor examples you could think of games like Advance Wars, Fire Emblem or Disgaea. I should say that I'm using design by component so far, but I can't find a nice way to fit components into the part I want to ask. I'm struggling right now with the "game rules" logic. That is, the code that displays the menu, allows the player to select units, and command them, then tells the unit game objects what to do given the player input. The best way I could thing of handling this was using a big state machine, so everything that could be done in a "turn" is handled by this state machine, and the update code of this state machine does different things depending on the state. This approach, though, leads to a large amount of code (anything not model-related) to go into a big class. Of course I can subdivide this big class into more classes, but it doesn't feel modular and upgradable enough. I'd like to know of better systems to handle this in order to be able to upgrade the game with new rules without having a monstruous if/else chain (or switch / case, for that matter). So, any ideas? I'd also like to ask that if you recommend me a specific design pattern to also provide some kind of example or further explanation and not stick to "Yeah you should use MVC and it'll work".

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• How to use the unit of work and repository patterns in a service oriented enviroment

  - by A. Karimi

  I've created an application framework using the unit of work and repository patterns for it's data layer. Data consumer layers such as presentation depend on the data layer design. For example a CRUD abstract form has a dependency to a repository (IRepository). This architecture works like a charm in client/server environments (Ex. a WPF application and a SQL Server). But I'm looking for a good pattern to change or reuse this architecture for a service oriented environment. Of course I have some ideas: Idea 1: The "Adapter" design pattern Keep the current architecture and create a new unit of work and repository implementation which can work with a service instead of the ORM. Data layer consumers are loosely coupled to the data layer so it's possible but the problem is about the unit of work; I have to create a context which tracks the objects state at the client side and sends the changes to the server side on calling the "Commit" (Something that I think the RIA has done for Silverlight). Here the diagram: ----------- CLIENT----------- | ------------------ SERVER ---------------------- [ UI ] -> [ UoW/Repository ] ---> [ Web Services ] -> [ UoW/Repository ] -> [DB] Idea 2: Add another layer Add another layer (let say "local services" or "data provider"), then put it between the data layer (unit of work and repository) and the data consumer layers (like UI). Then I have to rewrite the consumer classes (CRUD and other classes which are dependent to IRepository) to depend on another interface. And the diagram: ----------------- CLIENT ------------------ | ------------------- SERVER --------------------- [ UI ] -> [ Local Services/Data Provider ] ---> [ Web Services ] -> [ UoW/Repository ] -> [DB] Please note that I have the local services layer on the current architecture but it doesn't expose the data layer functionality. In another word the UI layer can communicate with both of the data and local services layers whereas the local services layer also uses the data layer. | | | | | | | | ---> | Local Services | ---> | | | UI | | | | Data | | | | | | | ----------------------------> | |

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• How common is prototyping as the first stage of development?

  - by EpsilonVector

  I've been taking some software design courses in the past few semesters, and while I see the benefit in a lot of the formalism, I feel like it doesn't tell me anything about the program itself: You can't tell how the program is going to operate from the Use Case spec, even though it discusses what the program can do. You can't tell anything about the user experience from the requirements document, even though it can include quality requirements. Sequence diagrams are a good description of how the software works as the call stack, but are very limited, and give a highly partial view of the overall system. Class diagrams are great for describing how the system is built, but are utterly useless in helping you figure out what the software needs to be. Where in all this formalism is the bottom line: how the program looks, operates, and what experience it gives? Doesn't it make more sense to design off of that? Isn't it better to figure out how the program should work via a prototype and strive to implement it for real? I know that I'm probably suffering from being taught engineering by theoreticians, but I need to ask, do they do this in the industry? How do people figure out what the program actually is, not what it should conform to? Do people prototype a lot, or do they mostly use the formal tools like UML and I just didn't get the hang of using them yet?

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• How common is prototyping as the first stage of development?

  - by EpsilonVector

  I've been taking some software design courses in the past few semesters, and while I see the benefit in a lot of the formalism, I still feel like it doesn't tell me anything about the program itself. You can't tell how the program is going to operate from the Use Case spec, even though it discusses what the program can do, and you can't tell anything about the user experience from the requirements document, even though it can include QA requirements. ...sequence diagrams are as good a description of how the software works as the call stack, in other words- very limited, highly partial view of the overall system, and a class diagram is great for describing how the system is built, but is utterly useless in helping you figure out what the software needs to be. Where in all this formalism is the bottom line- how the program looks, operates, and what experience it gives? Doesn't it make more sense to design off of that? Isn't it better to figure out how the program should work via a prototype and strive to implement it for real? I know that I'm probably suffering from being taught engineering by theoreticians, but I got to ask, do they do this in the industry? How do people figure out what the program actually is, not what it should conform to? Do people prototype a lot? ...or do they mostly use the formal tools like UML and I just didn't get the hang of using them yet?

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• How or why would this mechanic (not) work to bring game balance to a singleplayer RPG? [closed]

  - by 0xFFF1

  Mechanic details The player, the monsters, and the merchants act as three separate parties. The player needs to beat up monsters for exp points and resources to sell and to buy potions from merchants to continue to fight. The monsters need healing and reviving to survive (also bought from merchants) and the merchants need potion ingredients from the player and the monsters to make potions to sell. These potions are only able to be processed in such bulk by merchants thus their potions would be cheaper than making them yourself. Only the monsters can farm ingredients in bulk. Only the player is or has to be overly aggressive (in bulk). Monsters can farm and produce "Level up candies" that do the work of exp. they are eaten right away after they are made and are never stockpiled or held for fear of the player and merchants who want to sell to the player. The monsters will defend themselves. Reviving is very expensive. The merchants can be found either with a concerned expression or a grinning expression based on how much profit they are making compared to their morale standing. The economies of each monster town and merchant city are distinct but interconnected. Magic Swords are worth a lot. So what I need to know is what concerns would there be to design a game around this mechanic and/or design this mechanic around a developing game. which would fare better? Is game balance an issue here? (how strong the monsters get or how quickly they die off based on the player's input into the system), Or is game balance solely in the hands of the player? (he decides if he overkills monsters or get underleveled.) What do I need to think about to make sure it isn't too easy or too hard to swing the amount/strength of monsters compared to the player and the amount of profit the merchants get vs the player. Would indicating how out of whack things are getting in game help with this?

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• Be liberal in what you accept... or not?

  - by Matthieu M.

  [Disclaimer: this question is subjective, but I would prefer getting answers backed by facts and/or reflexions] I think everyone knows about the Robustness Principle, usually summed up by Postel's Law: Be conservative in what you send; be liberal in what you accept. I would agree that for the design of a widespread communication protocol this may make sense (with the goal of allowing easy extension), however I have always thought that its application to HTML / CSS was a total failure, each browser implementing its own silent tweak detection / behavior, making it near impossible to obtain a consistent rendering across multiple browsers. I do notice though that there the RFC of the TCP protocol deems "Silent Failure" acceptable unless otherwise specified... which is an interesting behavior, to say the least. There are other examples of the application of this principle throughout the software trade that regularly pop up because they have bitten developpers, from the top off my head: Javascript semi-colon insertion C (silent) builtin conversions (which would not be so bad if it did not truncated...) and there are tools to help implement "smart" behavior: name matching phonetic algorithms (Double Metaphone) string distances algorithms (Levenshtein distance) However I find that this approach, while it may be helpful when dealing with non-technical users or to help users in the process of error recovery, has some drawbacks when applied to the design of library/classes interface: it is somewhat subjective whether the algorithm guesses "right", and thus it may go against the Principle of Least Astonishment it makes the implementation more difficult, thus more chances to introduce bugs (violation of YAGNI ?) it makes the behavior more susceptible to change, as any modification of the "guess" routine may break old programs, nearly excluding refactoring possibilities... from the start! And this is what led me to the following question: When designing an interface (library, class, message), do you lean toward the robustness principle or not ? I myself tend to be quite strict, using extensive input validation on my interfaces, and I was wondering if I was perhaps too strict.

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• Capitalizing on JavaScript's prototypal inheritance

  - by keithjgrant

  JavaScript has a class-free object system in which objects inherit properties directly from other objects. This is really powerful, but it is unfamiliar to classically trained programmers. If you attempt to apply classical design patterns directly to JavaScript, you will be frustrated. But if you learn to work with JavaScript's prototypal nature, your efforts will be rewarded. ... It is Lisp in C's clothing. -Douglas Crockford What does this mean for a game developer working with canvas and HTML5? I've been looking over this question on useful design patterns in gaming, but prototypal inheritance is very different than classical inheritance, and there are surely differences in the best way to apply some of these common patterns. For example, classical inheritance allows us to create a moveableEntity class, and extend that with any classes that move in our game world (player, monster, bullet, etc.). Sure, you can strongarm JavaScript to work that way, but in doing so, you are kind of fighting against its nature. Is there a better approach to this sort of problem when we have prototypal inheritance at our fingertips?

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• Testcase runner for parametrized testcases

  - by Razer

  Let me explain my situation. I'm planning a kind of test case runner for doing testcases on external devices, which are microcontroller based. Lets consider the devices: Device 1 Device 2 There exist a lot of test cases which can be run with one of the devices above. For example: Testcase 1 Testcase 2 The main reason that all the testcases can be run with any device is, that the testcases validates some standard and this software should be extensible for future devices. The testcases itself must be runnable with changing parameters. For example Testcase 1 does some Timing Verification the testcase needs as input parameter the datarate: 4800, 9600, 19200. Now hoping you understand the situation, let me explain my design questions. For implementing the test cases I thought about an Attribute based approach, like nunit does it. The more complicated problem is, how to define the parametrized testcases? Like this: Device 1: Testcase 1: datarate: 4800, 9600, 19200 Testcase 2: supply: 1, 2, 3 Device 2: Testcase 1: datarate: 9600, 19200, 38400 Testcase 2: supply: 3, 4, 5 How would you design such a framework? I've done a similar desin in python where I had for every device a XML containing the testcase definitions like: <Testcase="Testcase 1" datarate=4800/> <Testcase="Testcase 1" datarate=9600/> <Testcase="Testcase 1" datarate=19200/>

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• Designing web-based plugin systems correctly so they don't waste as many resources?

  - by Xeoncross

  Many CMS systems which rely on third parties for much of their code often build "plugin" or "hooks" systems to make it easy for developers to modify the codebase's actions without editing the core files. This usually means an Observer or Event design pattern. However, when you look at systems like wordpress you see that on every page they load some kind of bootstrap file from each of the plugin's folders to see if that plugin will need to run that request. Its this poor design that causes systems like wordpress to spend many extra MB's of memory loading and parsing unneeded items each page. Are there alternative ways to do this? I'm looking for ideas in building my own. For example, Is there a way to load all this once and then cache the results so that your system knows how to lazy-load plugins? In other words, the system loads a configuration file that specifies all the events that plugin wishes to tie into and then saves it for future requests? If that also performs poorly, then perhaps there is a special file-structure that could be used to make educated guesses about when certain plugins are unneeded to fullfil the request. Any ideas? If anyone wants an example of the "plugin" concept you can find one here.

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• Designing a plug-in system

  - by madflame991

  I'm working on a Java project and I would like to add a plug-in system. More precisely, I would like to let the user design his own module, pack it into a jar, leave it in a "plugins/" subfolder of my application and be done with it. I've managed to get a child classloader to instantiate objects of classes located in external jars, but now I'm facing a design dilemma: Say Joe makes a plug-in and he packs it in joeplugin.jar. I would really like Joe to have a class named "instantiation.Factory" and I would also like everyone to have this class with this exact location and name. (This factory class obviously implements a interface that I provide and through it I get what I want from the plug-in.) If Joe wouldn't be restricted in this way I would have to look into his entire jar for some class that implements my factory interface and I don't want to imagine how complicated things get. So my question is: should I enforce a strict naming convention for this single class? I have no idea how plug-in systems work.

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• Procedural content (settlement) generation

  - by instancedName

  I have, lets say, something like a homework or assignment to do. Roughly said I need to write an algorithm (pseudo code is not necessary, just in depth description) of procedure that would generate settlements, environment and a people to populate it with, as part of some larger world generation procedure. The genre of game is not specified, it could be any genre (rpg, strategy, colony simulation etc.) where interacting with large and extensive world is central to the game. Procedure should be called once per settlement. At the time of calling, world generation procedure makes geography, culture and history input available. Output should be map of the village and it's immediate area, and various potential additional information like myths, history, demographic facts etc. Bonus would be quest ant similar stuff, but that not really my focus at the moment. I will leave quality of the output for later when I actually dig little deeper into this topic. I am free to change parameters as long as I have strong explanation for doing so. Setting of the game is undetermined so I am free to use anything that I like the most. Ok, so my actual question is: Can anyone who has some experience in this field of game design recommend me some good literature, or point me in the direction where I should look/reed/study? I'm somewhat experienced game programmer, but I've never been into game design till now so any help will be great. I want to do this assignment as good as I can. As for deadline, it's not strictly set, but lets say I don't want it to take longer then few weeks, one month at worst case.

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• First Project a big one, How much should we charge?

  - by confuzzled

  Two of my cousins and I started a freelance computer repair/web design business just to make some money on the side during college, and received our first major web design project about three weeks ago. Now we've created websites before, but it was mostly for family businesses and have never really charged money, and most of the websites have been static, and don't really require a CMS. This project, however, was a big one (for us anyways). We created a news site that had several categories, we created the banners, we created a classifieds page (not a web app just something static that they control). Several links, a few graphical assets, CSS drop down menu, RSS feed from a different news site, weather, all the normal stuff you would find on a regular news site. On top of that we put in all the usual Joomla stuff (search, Jcomments, Jslide pictures, JCE, etc.). Then we uploaded the first 10 articles they gave us, and we are going to train them how to use Joomla. Now, at first we decided for 700 dollars. I assumed they just wanted a simple blog like website where they can upload articles. But then we had a meeting, and they asked for a lot more. Note: we did not hard code the template from scratch, but customized the gantry framework to fit their needs. We did code quite a bit however. I estimate that we put in about 50-60 hours in total. I'm wondering if 700 dollars is a bit low, this price is definitely not set in stone. Please keep in mind that this is our first project, and we are newbies, please be kind. Thank You!

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• What do you wish language designers paid attention to?

  - by Berin Loritsch

  The purpose of this question is not to assemble a laundry list of programming language features that you can't live without, or wish was in your main language of choice. The purpose of this question is to bring to light corners of languge design most language designers might not think about. So, instead of thinking about language feature X, think a little more philisophically. One of my biases, and perhaps it might be controversial, is that the softer side of engineering--the whys and what fors--are many times more important than the more concrete side. For example, Ruby was designed with a stated goal of improving developer happiness. While your opinions may be mixed on whether it delivered or not, the fact that was a goal means that some of the choices in language design were influenced by that philosophy. Please do not post: Syntax flame wars (I could care less whether you use whitespace [Python], keywords [Ruby], or curly braces [Java, C/C++, et. al.] to denote program blocks). That's just an implementation detail. "Any language that doesn't have feature X doesn't deserve to exist" type comments. There is at least one reason for all programming languages to exist--good or bad. Please do post: Philisophical ideas that language designers seem to miss. Technical concepts that seem to be poorly implemented more often than not. Please do provide an example of the pain it causes and if you have any ideas of how you would prefer it to function. Things you wish were in the platform's common library but seldom are. One the same token, things that usually are in a common library that you wish were not. Conceptual features such as built in test/assertion/contract/error handling support that you wish all programming languages would implement properly--and define properly. My hope is that this will be a fun and stimulating topic.

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• Making money from a custom built interpreter?

  - by annoying_squid

  I have been making considerable progress lately on building an interpreter. I am building it from NASM assembly code (for the core engine) and C (cl.exe the Microsoft compiler for the parser). I really don't have a lot of time but I have a lot of good ideas on how to build this so it appeals to a certain niche market. I'd love to finish this but I need to face reality here ... unless I can make some good monetary return on my investment, there is not a lot of time for me to invest. So I ask the following questions to anyone out there, especially those who have experience in monetizing their programs: 1) How easy is it for a programmer to make good money from one design? (I know this is vague but it will be interesting to hear from those who have experience or know of others' experiences). 2) What are the biggest obstacles to making money from a programming design? 3) For the parser, I am using the Microsoft compiler (no IDE) I got from visual express, so will this be an issue? Will I have to pay royalties or a license fee? 4) As far as I know NASM is a 2-clause BSD licensed application. So this should allow me to use NASM for commericial development unless I am missing something? It's good to know these things before launching into the meat and potatoes of the project.

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• Testing of visualization projects

  - by paxRoman

  We develop small to large visualization projects for different tasks and industries and sometimes while rewriting them a couple of times in the process we hit walls because we discover that we need to add a lot of code to support new requirements. Now we have established a design process that seems to work well (at least we reduced the development time for each new project quite a bit), but we're still left scratching our heads around this question: what exactly should we test when testing visualizations? If everything that we want to explore is on the screen (bounded visualizations)? If the data is ok - if data is valid (that's one of the nice things about visualizations you can spot errors in your datasets)? Usability? User interaction? Code quality? I can tell you for sure that a simple check of the code quality is certainly not enough! Is there a classic paper / book about how to test visualizations? Also do you happen to know about classic design patterns for visualizations (except the obvious ones like Pub-Sub)?

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• Is there a canonical source supporting "all-surrogates"?

  - by user61852

  Background The "all-PK-must-be-surrogates" approach is not present in Codd's Relational Model or any SQL Standard (ANSI, ISO or other). Canonical books seems to elude this restrictions too. Oracle's own data dictionary scheme uses natural keys in some tables and surrogate keys in other tables. I mention this because these people must know a thing or two about RDBMS design. PPDM (Professional Petroleum Data Management Association) recommend the same canonical books do: Use surrogate keys as primary keys when: There are no natural or business keys Natural or business keys are bad ( change often ) The value of natural or business key is not known at the time of inserting record Multicolumn natural keys ( usually several FK ) exceed three columns, which makes joins too verbose. Also I have not found canonical source that says natural keys need to be immutable. All I find is that they need to be very estable, i.e need to be changed only in very rare ocassions, if ever. I mention PPDM because these people must know a thing or two about RDBMS design too. The origins of the "all-surrogates" approach seems to come from recommendations from some ORM frameworks. It's true that the approach allows for rapid database modeling by not having to do much business analysis, but at the expense of maintainability and readability of the SQL code. Much prevision is made for something that may or may not happen in the future ( the natural PK changed so we will have to use the RDBMS cascade update funtionality ) at the expense of day-to-day task like having to join more tables in every query and having to write code for importing data between databases, an otherwise very strightfoward procedure (due to the need to avoid PK colisions and having to create stage/equivalence tables beforehand ). Other argument is that indexes based on integers are faster, but that has to be supported with benchmarks. Obviously, long, varying varchars are not good for PK. But indexes based on short, fix-length varchar are almost as fast as integers. The questions - Is there any canonical source that supports the "all-PK-must-be-surrogates" approach ? - Has Codd's relational model been superceded by a newer relational model ?

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• Web Services and code lists

  - by 0x0me

  Our team heavily discuss the issues how to handle code list in a web service definition. The design goal is to describe a provider API to query a system using various values. Some of them are catalogs resp. code lists. A catalog or code list is a set of key value pairs. There are different systems (at least 3) maintaining possibly different code lists. Each system should implement the provider API, whereas each system might have different code list for the same business entity eg. think of colors. One system know [(1,'red'),(2,'green')] and another one knows [(1,'lightgreen'),(2,'darkgreen'),(3,'red')] etc. The access to the different provider API implementations will be encapsulated by a query service, but there is already one candidate which might use at least one provider API directly. The current options to design the API discussed are: use an abstract code list in the interface definition: the web service interface defines a well known set of code list which are expected to be used for querying and returning data. Each API provider implementation has to mapped the request and response values from those abstract codelist to the system specific one. let the query component handle the code list: the encapsulating query service knows the code list set of each provider API implementation and takes care of mapping the input and output to the system specific code lists of the queried system. do not use code lists in the query definition at all: Just query code lists by a plain string and let the provider API implementation figure out the right value. This might lead to a loose of information and possibly many false positives, due to the fact that the input string could not be canonical mapped to a code list value (eg. green - lightgreen or green - darkgreen or both) What are your experiences resp. solutions to such a problem? Could you give any recommendation?

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• Looking for a better Factory pattern (Java)

  - by Sam Goldberg

  After doing a rough sketch of a high level object model, I am doing iterative TDD, and letting the other objects emerge as a refactoring of the code (as it increases in complexity). (That whole approach may be a discussion/argument for another day.) In any case, I am at the point where I am looking to refactor code blocks currently in an if-else blocks into separate objects. This is because there is another another value combination which creates new set of logical sub-branches. To be more specific, this is a trading system feature, where buy orders have different behavior than sell orders. Responses to the orders have a numeric indicator field which describes some event that occurred (e.g. fill, cancel). The combination of this numeric indicator field plus whether it is a buy or sell, require different processing buy the code. Creating a family of objects to separate the code for the unique handling each of the combinations of the 2 fields seems like a good choice at this point. The way I would normally do this, is to create some Factory object which when called with the 2 relevant parameters (indicator, buysell), would return the correct subclass of the object. Some times I do this pattern with a map, which allows to look up a live instance (or constructor to use via reflection), and sometimes I just hard code the cases in the Factory class. So - for some reason this feels like not good design (e.g. one object which knows all the subclasses of an interface or parent object), and a bit clumsy. Is there a better pattern for solving this kind of problem? And if this factory method approach makes sense, can anyone suggest a nicer design?

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• Using visitor pattern with large object hierarchy

  - by T. Fabre

  Context I've been using with a hierarchy of objects (an expression tree) a "pseudo" visitor pattern (pseudo, as in it does not use double dispatch) : public interface MyInterface { void Accept(SomeClass operationClass); } public class MyImpl : MyInterface { public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } } This design was, however questionnable, pretty comfortable since the number of implementations of MyInterface is significant (~50 or more) and I didn't need to add extra operations. Each implementation is unique (it's a different expression or operator), and some are composites (ie, operator nodes that will contain other operator/leaf nodes). Traversal is currently performed by calling the Accept operation on the root node of the tree, which in turns calls Accept on each of its child nodes, which in turn... and so on... But the time has come where I need to add a new operation, such as pretty printing : public class MyImpl : MyInterface { // Property does not come from MyInterface public string SomeProperty { get; set; } public void Accept(SomeClass operationClass) { operationClass.DoSomething(); operationClass.DoSomethingElse(); // ... and so on ... } public void Accept(SomePrettyPrinter printer) { printer.PrettyPrint(this.SomeProperty); } } I basically see two options : Keep the same design, adding a new method for my operation to each derived class, at the expense of maintainibility (not an option, IMHO) Use the "true" Visitor pattern, at the expense of extensibility (not an option, as I expect to have more implementations coming along the way...), with about 50+ overloads of the Visit method, each one matching a specific implementation ? Question Would you recommand using the Visitor pattern ? Is there any other pattern that could help solve this issue ?

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• Modular Architecture for Processing Pipeline

  - by anjruu

  I am trying to design the architecture of a system that I will be implementing in C++, and I was wondering if people could think of a good approach, or critique the approach that I have designed so far. First of all, the general problem is an image processing pipeline. It contains several stages, and the goal is to design a highly modular solution, so that any of the stages can be easily swapped out and replaced with a piece of custom code (so that the user can have a speed increase if s/he knows that a certain stage is constrained in a certain way in his or her problem). The current thinking is something like this: struct output; /*Contains the output values from the pipeline.*/ class input_routines{ public: virtual foo stage1(...){...} virtual bar stage2(...){...} virtual qux stage3(...){...} ... } output pipeline(input_routines stages); This would allow people to subclass input_routines and override whichever stage they wanted. That said, I've worked in systems like this before, and I find the subclassing and the default stuff tends to get messy, and can be difficult to use, so I'm not giddy about writing one myself. I was also thinking about a more STLish approach, where the different stages (there are 6 or 7) would be defaulted template parameters. Can anyone offer a critique of the pattern above, thoughts on the template approach, or any other architecture that comes to mind?

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• ASP.NET Webforms developers and web designers: how to interact?

  - by just_name

  I'm an ASP.NET Webforms developer, and I face some problems when I deal with designers. Designers always complain about the asp.net server controls. They'd rather just have an html file and create css files along with the required images to go with those. Sometimes, if the design phase is done in advance, I get html files with related css files, but then we face many problems integrating the design with the aspx files (sever controls an telerik controls ... etc). What I want to ask about is: How do I overcome these problems? The designers prefer php- and mvc developers because of the problems with .net server controls. I need to know how to interact with the designers in the correct way. Are there any tools or applications to provide the designers with the rendered (html page) of the .aspx pages? By that I mean the page in runtime rather than the aspx in Visual Studio. They do use Web Expression but they want the rendered page in html as well.

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