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• Concurrency pattern of logger in multithreaded application

  - by Dipan Mehta

  The context: We are working on a multi-threaded (Linux-C) application that follows a pipeline model. Each module has a private thread and encapsulated objects which do processing of data; and each stage has a standard form of exchanging data with next unit. The application is free from memory leak and is threadsafe using locks at the point where they exchange data. Total number of threads is about 15- and each thread can have from 1 to 4 objects. Making about 25 - 30 odd objects which all have some critical logging to do. Most discussion I have seen about different levels as in Log4J and it's other translations. The real big questions is about how the overall logging should really happen? One approach is all local logging does fprintf to stderr. The stderr is redirected to some file. This approach is very bad when logs become too big. If all object instantiate their individual loggers - (about 30-40 of them) there will be too many files. And unlike above, one won't have the idea of true order of events. Timestamping is one possibility - but it is still a mess to collate. If there is a single global logger (singleton) pattern - it indirectly blocks so many threads while one is busy putting up logs. This is unacceptable when processing of the threads are heavy. So what should be the ideal way to structure the logging objects? What are some of the best practices in actual large scale applications? I would also love to learn from some of the real designs of large scale applications to get inspirations from!

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• Command Pattern refactor for input processing?

  - by Casey

  According to Game Coding Complete 4th. ed. processing input via the following is considered unmanagable and inflexible. But does not show an example. I've used the Command pattern to represent GUI button commands but could not figure out how to represent the input from the keyboard and/or mouse. if(g_keyboard->KeyDown(KEY_ESC)) { quit = true; return; } //Processing if(g_keyboard->KeyDown(KEY_T)) { g_show_test_gateway = !g_show_test_gateway; } if(g_mouse->ButtonDown(a2de::Mouse::BUTTON2)) { g_selected_part = GWPart::PART_NONE; SetMouseImageToPartImage(); } ResetButtonStates(); g_prevButton = g_curButton; g_curButton = GetButtonHovered(); if(g_curButton) { g_mouse->SetImageToDefault(); if(g_mouse->ButtonDown(a2de::Mouse::BUTTON1) || g_mouse->ButtonPress(a2de::Mouse::BUTTON1)) { ButtonPressCommand curCommand(g_curButton); curCommand.Execute(); } else if(g_mouse->ButtonUp(a2de::Mouse::BUTTON1)) { if(g_prevButton == g_curButton) { ButtonReleaseCommand curCommand(g_curButton); curCommand.Execute(); if(g_curButton->GetType() == "export") { ExportCommand curCommand(g_curButton, *g_gateway); curCommand.Execute(); } } else { ResetButtonStates(); } } else { ButtonHoverCommand curCommand(g_curButton); curCommand.Execute(); } } else { g_status_message.clear(); SetMouseImageToPartImage(); if(g_mouse->ButtonDown(a2de::Mouse::BUTTON1)) { CreatePartCommand curCommand(*g_gateway, g_selected_part, a2de::Vector2D(g_mouse->GetX(), g_mouse->GetY())); curCommand.Execute(); } }

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• What Pattern will solve this - fetching dependent record from database

  - by tunmise fasipe

  I have these classes class Match { int MatchID, int TeamID, //used to reference Team ... other fields } Note: Match actually have 2 teams which means 2 TeamID class Team { int TeamID, string TeamName } In my view I need to display List<Match> showing the TeamName. So I added another field class Match { int MatchID, int TeamID, //used to reference Team ... other fields string TeamName; } I can now do Match m = getMatch(id); m.TeamName = getTeamName(m.TeamId); //get name from database But for a List<Match>, getTeamName(TeamId) will go to the database to fetch TeamName for each TeamID. For a page of 10 Matches per page, that could be (10x2Teams)=20 trip to database. To avoid this, I had the idea of loading everything once, store it in memory and only lookup the TeamName in memory. This made me have a rethink that what if the records are 5000 or more. What pattern is used to solve this and how?

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• MVVM and service pattern

  - by alfa-alfa

  I'm building a WPF application using the MVVM pattern. Right now, my viewmodels calls the service layer to retrieve models (how is not relevant to the viewmodel) and convert them to viewmodels. I'm using constructor injection to pass the service required to the viewmodel. It's easily testable and works well for viewmodels with few dependencies, but as soon as I try to create viewModels for complex models, I have a constructor with a LOT of services injected in it (one to retrieve each dependencies and a list of all available values to bind to an itemsSource for example). I'm wondering how to handle multiple services like that and still have a viewmodel that I can unit test easily. I'm thinking of a few solutions: Creating a services singleton (IServices) containing all the available services as interfaces. Example: Services.Current.XXXService.Retrieve(), Services.Current.YYYService.Retrieve(). That way, I don't have a huge constructor with a ton of services parameters in them. Creating a facade for the services used by the viewModel and passing this object in the ctor of my viewmodel. But then, I'll have to create a facade for each of my complexe viewmodels, and it might be a bit much... What do you think is the "right" way to implement this kind of architecture ?

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• Ad-hoc taxonomy: owning the chess set doesn't mean you decide how the little horsey moves

  - by Roger Hart

  There was one of those little laugh-or-cry moments recently when I heard an anecdote about content strategy failings at a major online retailer. The story goes a bit like this: successful company in a highly commoditized marketplace succeeds on price and largely ignores its content team. Being relatively entrepreneurial, the founders are still knocking around, and occasionally like to "take an interest". One day, they decree that clothing sold on the site can no longer be described as "unisex", because this sounds old fashioned. Sad now. Let me just reiterate for the folks at the back: large retailer, commoditized market place, differentiating on price. That's inherently unstable. Sooner or later, they're going to need one or both of competitive differentiation and significant optimization. I can't speak for the latter, since I'm hypothesizing off a raft of rumour, but one of the simpler paths to the former is to become - or rather acknowledge that they are - a content business. Regardless, they need highly-searchable terminology. Even in the face of tooth and claw resistance to noticing the fundamental position content occupies in driving sales (and SEO) on the web, there's a clear information problem here. Dilettante taxonomy is a disaster. Ok, so this is a small example, but that kind of makes it a good one. Unisex probably is the best way of describing clothing designed to suit either men or women interchangeably. It certainly takes less time to type (and read). It's established terminology, and as a single word, it's significantly better for web readability than a phrasal workaround. Something like "fits men or women" is short, by could fall foul of clause-level discard in web scanning. It's not an adjective, so for intuitive reading it's never going to be near the start of a title or description. It would also clutter up search results, and impose cognitive load in list scanning. Sorry kids, it's just worse. Even if "unisex" were an archaism (which it isn't), the only thing that would weigh against its being more usable and concise terminology would be evidence that this archaism were hurting conversions. Good luck with that. We once - briefly - called one of our products a "Can of worms". It was a bundle in a bug-tracking suite, and we thought it sounded terribly cool. Guess how well that sold. We have information and content professionals for a reason: to make sure that whatever we put in front of users is optimised to meet user and business goals. If that thinking doesn't inform style guides, taxonomy, messaging, title structure, and so forth, you might as well be finger painting.

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• Strategy to allow emergency access to colocation crew

  - by itsadok

  I'm setting up a server at a new colocation center half way around the world. They installed the OS for me and sent me the root password, so there's obviously a great amount of trust in them. However, I'm pretty sure I don't want them to have my root password on a regular basis. And anyway, I intend to only allow key-based login. On some cases, though, it might be useful to let their technical support log in through a physical terminal. For example, if I somehow mess up the firewall settings. Should I even bother worrying about that? Should I set up a sudoer account with a one-time password that will change if I ever use it? Is there a common strategy for handling something like this?

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• Online Backup strategy for family individuals

  - by marlon brando

  The majority of my family, including myself, uses Dropbox and Syncplicity free accounts for our syncing needs. However our backup strategy is pretty non-existent, we all have access (via webDav) to our qnap nas located at home, however we copy files accross when we can remember to do so, terrible I know. Is there tools like CrashPlan or Spideroak that allows each the accomodation of each family members syncing and back-up needs under one main account? I'm not sure how this would work, as each family member would need a seperate sub-account or would I manage each computer's syncing and backup lists from a single account? Any thoughts?

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• Datacenter Backup Strategy

  - by EasyEcho

  What are common approaches to backup solutions in remote data centers? I am already familiar with general backup principals and have a very good backup strategy for our local data center but am having great difficulty extending it to a remote data center. We currently do a full backup on Friday, differential Mon - Thu, rotate offsite Friday morning ...rinse and repeat week after week. BTW, we use disks and have been very happy with this approach. We could buy a large storage server and backup everything to it, but this solution doesn't give you offsite. We could encrypt and upload to Amazon or some other online storage but that would take a large amount of time given the data and would be rather expensive paying for the bandwidth leaving the data center and receiving at amazon. We could drive to the data center every Friday and continue to rotate disks as we do now. But that just seems old fashion. What am I missing, are there better options?

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• Advice for an EC2 Architecture and Deployment Strategy

  - by Mark

  My company is currently migrating several websites and PHP web applications (standard LAMP stack) from three in-house servers to Amazon EC2. Because we had only three servers, we clustered several low-traffic websites with perhaps one high-traffic web application, and served them from the same server. The server admin has pretty much copied the previous architecture wholesale onto the EC2 instances, simply upping the instance size to account for the highest traffic client that occupies that particular instance. This architecture might be okay if it wasn't for deployment. Any time one of these sites/apps changes, it means redeploying the entire instance, along with the 30 sites/apps it hosts, instead of just updating one. How can we architect our cloud in a more modular fashion? Should each app get its own appropriately-sized instance? What is the best strategy for deployment in this type of situation?

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• Design pattern to handle queries using multiple models

  - by coderkane

  I am presented with a dilemma while trying to re-designing the class structure for my PHP/MySQL application to make it more elegant and conform it to the SOLID principle. The problem goes like this: Let as assume, there is an abstract class called person which has certain properties to define a generic person, such as name, age, date of birth etc. There are two classes, student, and teacher, that implements this abstract class. They add their own unique properties to it. I have designed all the three classes to include all the operational logic (details of which are not relevant in context of the question). Now, I need to create views/reports/data grids which contain details from multiple classes, for example, say, a list of all students doing projects in Chemistry mentored by a teacher whose name is the parameter to the query. This is just one example of a view, there are many different views in the application, which uses data from 3-4 tables, and each of them have multiple input parameters to generate them. Considering this particular example, I have written the relevant query using JOIN and the results are as expected and proper, now here is the dilemma: Keeping in mind the single responsibility principle, where should I keep this query? It does not belong to either Student class, or Teacher class or any other classes currently present. a) Should I create a new class, say dataView class, and design it as a MVC pattern and keep the query there? What about the other views? how do they fit in this architecture? b) Should I not keep the query in code at all, and make it DB View ? c) Am I completely wrong in the approach? If so what is the right approach? My considerations are as follows: a) should be easy to add new views later on if requirement comes, without having to copy-paste-modify code b) would like to make it as loosely coupled as possible so that if minor db structure changes happen, it does not break I did google searches on report design and OOP report generators, but all the result seem to focus on the visual design of the report rather than fetching the data. I have already taken care of the visual aspect of the report using MVC with html templates. I am sure this is a very fundamental problem with known solution, but I am somehow not able to find it (maybe searching with wrong keyword). Edit1: Modified the title to make it more relevant Edit2: The accepted answer got me thinking in the right direction and identify my design flaws, which eventually led me to find this question and the solution in Stack Overflow which gave me the detailed answer to clear the confusion.

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• AI to move custom-shaped spaceships (shape affecting movement behaviour)

  - by kaoD

  I'm designing a networked turn based 3D-6DOF space fleet combat strategy game which relies heavily on ship customization. Let me explain the game a bit, since you need to know a bit about it to set the question. What I aim for is the ability to create your own fleet of ships with custom shapes and attached modules (propellers, tractor beams...) which would give advantages and disadvantages to each ship, so you have lots of different fleet distributions. E.g., long ship with two propellers at the side would let the ship spin around that plane easily, bigger ships would move slowly unless you place lots of propellers at the back (therefore spending more "construction" points and energy when moving, and it will only move fast towards that direction.) I plan to balance all the game around this feature. The game would revolve around two phases: orders and combat phase. During the orders phase, you command the different ships. When all players finish the order phase, the combat phase begins and the ship orders get resolved in real-time for some time, then the action pauses and there's a new orders phase. The problem comes when I think about player input. To move a ship, you need to turn on or off different propellers if you want to steer, travel forward, brake, rotate in place... These propellers don't have to work at their whole power, so you can achieve more movement combinations with less propellers. I think this approach is a bit boring. The player doesn't want to fiddle with motors or anything, you just want to MOVE and KILL. The way I intend the player to give orders to these ships is by a destination and a rotation, and then the AI would calculate the correct propeller power to achive that movement and rotation. Propulsion doesn't have to be the same throught the entire turn calculation (after the orders have been given) so it would be cool if the ships reacted as they move, adjusting the power of the propellers for their needs dynamically, but it may be too hard to implement and it's not really needed for the game to work. In both cases, how would that AI decide which propellers to activate for the best (or at least not worst) trajectory to be achieved? I though about some approaches: Learning AI: The ship types would learn about their movement by trial and error, adjusting their behaviour with more uses, and finally becoming "smart". I don't want to get involved THAT far in AI coding, and I think it can be frustrating for the player (even if you can let it learn without playing.) Pre-calculated timestep movement: Upon ship creation, ALL possible movements are calculated for each propeller configuration and power for a given delta-time. Memory intensive, ugly, bad. Pre-calculated trajectories: The same as above but not for each delta-time but the whole trajectory, which would then be fitted as much as possible. Requires a fixed propeller configuration for the whole combat phase and is still memory intensive, ugly and bad. Continuous brute forcing: The AI continously checks ALL possible propeller configurations throughout the entire combat phase, precalculates a few time steps and decides which is the best one based on that. Con: what's good now might not be that good later, and it's too CPU intensive, ugly, and bad too. Single brute forcing: Same as above, but only brute forcing at the beginning of the simulation, so it needs constant propeller configuration throughout the entire combat phase. Coninuous angle check: This is not a full movement method, but maybe a way to discard "stupid" propeller configurations. Given the current propeller's normal vector and the final one, you can approximate the power needed for the propeller based on the angle. You must do this continuously throughout the whole combat phase. I figured this one out recently so I didn't put in too much thought. A priori, it has the "what's good now might not be that good later" drawback too, and it doesn't care about the other propellers which may act together to make a better propelling configuration. I'm really stuck here. Any ideas?

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• Validation and Error Generation when using the Data Mapper Pattern

  - by AndyPerlitch

  I am working on saving state of an object to a database using the data mapper pattern, but I am looking for suggestions/guidance on the validation and error message generation step (step 4 below). Here are the general steps as I see them for doing this: (1) The data mapper is used to get current info (assoc array) about the object in db: +=====================================================+ | person_id | name | favorite_color | age | +=====================================================+ | 1 | Andy | Green | 24 | +-----------------------------------------------------+ mapper returns associative array, eg. Person_Mapper::getPersonById($id) : $person_row = array( 'person_id' => 1, 'name' => 'Andy', 'favorite_color' => 'Green', 'age' => '24', ); (2) the Person object constructor takes this array as an argument, populating its fields. class Person { protected $person_id; protected $name; protected $favorite_color; protected $age; function __construct(array $person_row) { $this->person_id = $person_row['person_id']; $this->name = $person_row['name']; $this->favorite_color = $person_row['favorite_color']; $this->age = $person_row['age']; } // getters and setters... public function toArray() { return array( 'person_id' => $this->person_id, 'name' => $this->name, 'favorite_color' => $this->favorite_color, 'age' => $this->age, ); } } (3a) (GET request) Inputs of an HTML form that is used to change info about the person is populated using Person::getters <form> <input type="text" name="name" value="<?=$person->getName()?>" /> <input type="text" name="favorite_color" value="<?=$person->getFavColor()?>" /> <input type="text" name="age" value="<?=$person->getAge()?>" /> </form> (3b) (POST request) Person object is altered with the POST data using Person::setters $person->setName($_POST['name']); $person->setFavColor($_POST['favorite_color']); $person->setAge($_POST['age']); *(4) Validation and error message generation on a per-field basis - Should this take place in the person object or the person mapper object? - Should data be validated BEFORE being placed into fields of the person object? (5) Data mapper saves the person object (updates row in the database): $person_mapper->savePerson($person); // the savePerson method uses $person->toArray() // to get data in a more digestible format for the // db gateway used by person_mapper Any guidance, suggestions, criticism, or name-calling would be greatly appreciated.

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• Recommendation for a Strategy Game Engine for .NET?

  - by Fred F.

  Can anyone recommend a strategy game engine for the .net framework. I downloaded XNA, but it is way beyond my needs. I just want to create a turn based strategy game. I have searched and searched, but all I cannnot find any examples. I have asked for something similiar before, but have not gotten any good answers.

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• How pattern lock disbles screen lock in android

  - by CED

  Hi, In android 2.1, if we enable pattern lock, then the screen lock (slide to unlock) is not displayed and if pattern lock is disabled then screen lock is enabled again. Can someone point me out the java file in framework and the function where this happens. I mean when the screen is about to get locked, how does android decide that whether it will display pattern lock or screen lock and if pattern lock, how it prevents the screen lock from getting displayed.

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• iphone cache strategy

  - by venkat

  hi all i am new to cache strategy....i would like to know how to increase the loading speed of web pages in iphone application... using cache strategy...its fine to have a response with sample code.... advance thanks. with kind regards venkat

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• Design pattern for adding / removing elements

  - by de3

  Wikipedia's definition for Iterator pattern design: the Iterator pattern is a design pattern in which iterators are used to access the elements of an aggregate object sequentially without exposing its underlying implementation. Iterator interface in java provides the following methods hasNext() next() remove() Is there a pattern design, or a java interface for inserting / deleting elements, and getting length of the aggregate object, in addition to iterating them? I know remove() is an optional method that can be used once per call to next(), but I am implementing a circular FIFO array and need a method delete() independent of iterator's next().

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• strategy for observer pattern?

  - by fayer

  I want to use observer pattern for a logging system. We have got logObservers and logObservables. The class that will have to log something will implement iLogObservable and include these methods: private $logObservers = array(); public function addLogObserver($logObserver) { $this->logObservers[] = $logObserver; } public function removeLogObserver($logObserver) { $this->logObservers[] = $logObserver; } public function write($type, $message) { foreach($this->logObservers as $logObserver) { $logObserver->log($level, $message); ; } } Then I noticed, that a lot of classes that will use logging will have these methods and I have to copy paste. So isn't it better to have these methods in a class I call LogObservable or just Log and then use strategy (instantiate this class inside all classes that will have to log). When I change the methods in Log, all logObservables will be affected. However, I have not seen anyone use observer pattern with strategy pattern yet, but it seems to be very efficient and remove the duplications. What do you think?

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• WCF Rest services for use with the repository pattern?

  - by mark smith

  Hi there, I am considering moving my Service Layer and my data layer (repository pattern) to a WCF Rest service. So basically i would have my software installed locally (WPF client) which would call the Service Layer that exists via a Rest Service... The service layer would then call my data layer using a WCF Rest Service also OR maybe just call it via the DLL assembly I was hoping to understand what the performance would be like. Currently I have my datalayer and servicelayer installed locally via DLL Assemblies locally on the pc. Also i presume the WCF REST services won't support method overloading hance the same name but with a different signature?? I would really appreciate any feedback anyone can give. Thanks

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• Supporting users if they're not on your site

  - by Roger Hart

  Have a look at this Read Write Web article, specifically the paragraph in bold and the comments. Have a wry chuckle, or maybe weep for the future of humanity - your call. Then pause, and worry about information architecture. The short story: Read Write Web bumps up the Google rankings for "Facebook login" at the same time as Facebook makes UI changes, and a few hundred users get confused and leave comments on Read Write Web complaining about not being able to log in to their Facebook accounts.* Blindly clicking the first Google result is not a navigation behaviour I'd anticipated for folks visiting big names sites like Facebook. But then, I use Launchy and don't know where any of my files are, depend on Firefox auto-complete, view Facebook through my IM client, and don't need a map to find my backside with both hands. Not all our users behave in the same way, which means not all of our architecture is within our control, and people can get to your content in all sorts of ways. Even if the Read Write Web episode is a prank of some kind (there are, after all, plenty of folks who enjoy orchestrated trolling) it's still a useful reminder. Your users may take paths through and to your content you cannot control, and they are unlikely to deconstruct their assumptions along the way. I guess the meaningful question is: can you still support those users? If they get to you from Google instead of your front door, does what they find still make sense? Does your information architecture still work if your guests come in through the bathroom window? Ok, so here they broke into the house next door - you can't be expected to deal with that. But the rest is well worth thinking about. Other off-site interaction It's rarely going to be as funny as the comments at Read Write Web, but your users are going to do, say, and read things they think of as being about you and your products, in places you don't control. That's good. If you pay attention to it, you get data. Your users get a better experience. There are easy wins, too. Blogs, forums, social media &c. People may look for and find help with your product on blogs and forums, on Twitter, and what have you. They may learn about your brand in the same way. That's fine, it's an interaction you can be part of. It's time-consuming, certainly, but you have the option. You won't get a blogger to incorporate your site navigation just in case your users end up there, but you can be there when they do. Again, Anne Gentle, Gordon McLean and others have covered this in more depth than I could. Direct contact Sales people, customer care, support, they all talk to people. Are they sending links to your content? if so, which bits? Do they know about all of it? Do they have the content they need to support them - messaging that funnels sales, FAQ that are realistically frequent, detailed examples of things people want to do, that kind of thing. Are they sending links because users can't find the good stuff? Are they sending précis of your content, or re-writes, or brand new stuff? If so, does that mean your content isn't up to scratch, or that you've got content missing? Direct sales/care/support interactions are enormously valuable, and can help you know what content your users find useful. You can't have a table of contents or a "See also" in a phonecall, but your content strategy can support more interactions than browsing. *Passing observation about Facebook. For plenty if folks, it is  the internet. Its services are simple versions of what a lot of people use the internet for, and they're aggregated into one stop. Flickr, Vimeo, Wordpress, Twitter, LinkedIn, and all sorts of games, have Facebook doppelgangers that are not only friendlier to entry-level users, they're right there, behind only one layer of authentication. As such, it could own a lot of interaction convention. Heavy users may well not be tech-savvy, and be quite change averse. That doesn't make this episode not dumb, but I'm happy to go easy on 'em.

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• Best Design Pattern for Coupling User Interface Components and Data Structures

  - by szahn

  I have a windows desktop application with a tree view. Due to lack of a sound data-binding solution for a tree view, I've implemented my own layer of abstraction on it to bind nodes to my own data structure. The requirements are as follows: Populate a tree view with nodes that resemble fields in a data structure. When a node is clicked, display the appropriate control to modify the value of that property in the instance of the data structure. The tree view is populated with instances of custom TreeNode classes that inherit from TreeNode. The responsibility of each custom TreeNode class is to (1) format the node text to represent the name and value of the associated field in my data structure, (2) return the control used to modify the property value, (3) get the value of the field in the control (3) set the field's value from the control. My custom TreeNode implementation has a property called "Control" which retrieves the proper custom control in the form of the base control. The control instance is stored in the custom node and instantiated upon first retrieval. So each, custom node has an associated custom control which extends a base abstract control class. Example TreeNode implementation: //The Tree Node Base Class public abstract class TreeViewNodeBase : TreeNode { public abstract CustomControlBase Control { get; } public TreeViewNodeBase(ExtractionField field) { UpdateControl(field); } public virtual void UpdateControl(ExtractionField field) { Control.UpdateControl(field); UpdateCaption(FormatValueForCaption()); } public virtual void SaveChanges(ExtractionField field) { Control.SaveChanges(field); UpdateCaption(FormatValueForCaption()); } public virtual string FormatValueForCaption() { return Control.FormatValueForCaption(); } public virtual void UpdateCaption(string newValue) { this.Text = Caption; this.LongText = newValue; } } //The tree node implementation class public class ExtractionTypeNode : TreeViewNodeBase { private CustomDropDownControl control; public override CustomControlBase Control { get { if (control == null) { control = new CustomDropDownControl(); control.label1.Text = Caption; control.comboBox1.Items.Clear(); control.comboBox1.Items.AddRange( Enum.GetNames( typeof(ExtractionField.ExtractionType))); } return control; } } public ExtractionTypeNode(ExtractionField field) : base(field) { } } //The custom control base class public abstract class CustomControlBase : UserControl { public abstract void UpdateControl(ExtractionField field); public abstract void SaveChanges(ExtractionField field); public abstract string FormatValueForCaption(); } //The custom control generic implementation (view) public partial class CustomDropDownControl : CustomControlBase { public CustomDropDownControl() { InitializeComponent(); } public override void UpdateControl(ExtractionField field) { //Nothing to do here } public override void SaveChanges(ExtractionField field) { //Nothing to do here } public override string FormatValueForCaption() { //Nothing to do here return string.Empty; } } //The custom control specific implementation public class FieldExtractionTypeControl : CustomDropDownControl { public override void UpdateControl(ExtractionField field) { comboBox1.SelectedIndex = comboBox1.FindStringExact(field.Extraction.ToString()); } public override void SaveChanges(ExtractionField field) { field.Extraction = (ExtractionField.ExtractionType) Enum.Parse(typeof(ExtractionField.ExtractionType), comboBox1.SelectedItem.ToString()); } public override string FormatValueForCaption() { return string.Empty; } The problem is that I have "generic" controls which inherit from CustomControlBase. These are just "views" with no logic. Then I have specific controls that inherit from the generic controls. I don't have any functions or business logic in the generic controls because the specific controls should govern how data is associated with the data structure. What is the best design pattern for this?

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• techniques for an AI for a highly cramped turn-based tactics game

  - by Adam M.

  I'm trying to write an AI for a tactics game in the vein of Final Fantasy Tactics or Vandal Hearts. I can't change the game rules in any way, only upgrade the AI. I have experience programming AI for classic board games (basically minimax and its variants), but I think the branching factor is too great for the approach to be reasonable here. I'll describe the game and some current AI flaws that I'd like to fix. I'd like to hear ideas for applicable techniques. I'm a decent enough programmer, so I only need the ideas, not an implementation (though that's always appreciated). I'd rather not expend effort chasing (too many) dead ends, so although speculation and brainstorming are good and probably helpful, I'd prefer to hear from somebody with actual experience solving this kind of problem. For those who know it, the game is the land battle mini-game in Sid Meier's Pirates! (2004) and you can skim/skip the next two paragraphs. For those who don't, here's briefly how it works. The battle is turn-based and takes place on a 16x16 grid. There are three terrain types: clear (no hindrance), forest (hinders movement, ranged attacks, and sight), and rock (impassible, but does not hinder attacks or sight). The map is randomly generated with roughly equal amounts of each type of terrain. Because there are many rock and forest tiles, movement is typically very cramped. This is tactically important. The terrain is not flat; higher terrain gives minor bonuses. The terrain is known to both sides. The player is always the attacker and the AI is always the defender, so it's perfectly valid for the AI to set up a defensive position and just wait. The player wins by killing all defenders or by getting a unit to the city gates (a tile on the other side of the map). There are very few units on each side, usually 4-8. Because of this, it's crucial not to take damage without gaining some advantage from it. Units can take multiple actions per turn. All units on one side move before any units on the other side. Order of execution is important, and interleaving of actions between units is often useful. Units have melee and ranged attacks. Melee attacks vary widely in strength; ranged attacks have the same strength but vary in range. The main challenges I face are these: Lots of useful move combinations start with a "useless" move that gains no immediate advantage, or even loses advantage, in order to set up a powerful flank attack in the future. And, since the player units are stronger and have longer range, the AI pretty much always has to take some losses before they can start to gain kills. The AI must be able to look ahead to distinguish between sacrificial actions that provide a future benefit and those that don't. Because the terrain is so cramped, most of the tactics come down to achieving good positioning with multiple units that work together to defend an area. For instance, two defenders can often dominate a narrow pass by positioning themselves so an enemy unit attempting to pass must expose itself to a flank attack. But one defender in the same pass would be useless, and three units can defend a slightly larger pass. Etc. The AI should be able to figure out where the player must go to reach the city gates and how to best position its few units to cover the approaches, shifting, splitting, or combining them appropriately as the player moves. Because flank attacks are extremely deadly (and engineering flank attacks is key to the player strategy), the AI should be competent at moving its units so that they cover each other's flanks unless the sacrifice of a unit would give a substantial benefit. They should also be able to force flank attacks on players, for instance by threatening a unit from two different directions such that responding to one threat exposes the flank to the other. The AI should attack if possible, but sometimes there are no good ways to approach the player's position. In that case, the AI should be able to recognize this and set up a defensive position of its own. But the AI shouldn't be vulnerable to a trivial exploit where the player repeatedly opens and closes a hole in his defense and shoots at the AI as it approaches and retreats. That is, the AI should ideally be able to recognize that the player is capable of establishing a solid defense of an area, even if the defense is not currently in place. (I suppose if a good unit allocation algorithm existed, as needed for the second bullet point, the AI could run it on the player units to see where they could defend.) Because it's important to choose a good order of action and interleave actions between units, it's not as simple as just finding the best move for each unit in turn. All of these can be accomplished with a minimax search in theory, but the search space is too large, so specialized techniques are needed. I thought about techniques such as influence mapping, but I don't see how to use the technique to great effect. I thought about assigning goals to the units. This can help them work together in some limited way, and the problem of "how do I accomplish this goal?" is easier to solve than "how do I win this battle?", but assigning good goals is a hard problem in itself, because it requires knowing whether the goal is achievable and whether it's a good use of resources. So, does anyone have specific ideas for techniques that can help cleverize this AI? Update: I found a related question on Stackoverflow: http://stackoverflow.com/questions/3133273/ai-for-a-final-fantasy-tactics-like-game The selected answer gives a decent approach to choosing between alternative actions, but it doesn't seem to have much ability to look into the future and discern beneficial sacrifices from wasteful ones. It also focuses on a single unit at a time and it's not clear how it could be extended to support cooperation between units in defending or attacking.

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• Design Pattern for Complex Data Modeling

  - by Aaron Hayman

  I'm developing a program that has a SQL database as a backing store. As a very broad description, the program itself allows a user to generate records in any number of user-defined tables and make connections between them. As for specs: Any record generated must be able to be connected to any other record in any other user table (excluding itself...the record, not the table). These "connections" are directional, and the list of connections a record has is user ordered. Moreover, a record must "know" of connections made from it to others as well as connections made to it from others. The connections are kind of the point of this program, so there is a strong possibility that the number of connections made is very high, especially if the user is using the software as intended. A record's field can also include aggregate information from it's connections (like obtaining average, sum, etc) that must be updated on change from another record it's connected to. To conserve memory, only relevant information must be loaded at any one time (can't load the entire database in memory at load and go from there). I cannot assume the backing store is local. Right now it is, but eventually this program will include syncing to a remote db. Neither the user tables, connections or records are known at design time as they are user generated. I've spent a lot of time trying to figure out how to design the backing store and the object model to best fit these specs. In my first design attempt on this, I had one object managing all a table's records and connections. I attempted this first because it kept the memory footprint smaller (records and connections were simple dicts), but maintaining aggregate and link information between tables became....onerous (ie...a huge spaghettified mess). Tracing dependencies using this method almost became impossible. Instead, I've settled on a distributed graph model where each record and connection is 'aware' of what's around it by managing it own data and connections to other records. Doing this increases my memory footprint but also let me create a faulting system so connections/records aren't loaded into memory until they're needed. It's also much easier to code: trace dependencies, eliminate cycling recursive updates, etc. My biggest problem is storing/loading the connections. I'm not happy with any of my current solutions/ideas so I wanted to ask and see if anybody else has any ideas of how this should be structured. Connections are fairly simple. They contain: fromRecordID, fromTableID, fromRecordOrder, toRecordID, toTableID, toRecordOrder. Here's what I've come up with so far: Store all the connections in one big table. If I do this, either I load all connections at once (one big db call) or make a call every time a user table is loaded. The big issue here: the size of the connections table has the potential to be huge, and I'm afraid it would slow things down. Store in separate tables all the outgoing connections for each user table. This is probably the worst idea I've had. Now my connections are 'spread out' over multiple tables (one for each user table), which means I have to make a separate DB called to each table (or make a huge join) just to find all the incoming connections for a particular user table. I've avoided making "one big ass table", but I'm not sure the cost is worth it. Store in separate tables all outgoing AND incoming connections for each user table (using a flag to distinguish between incoming vs outgoing). This is the idea I'm leaning towards, but it will essentially double the total DB storage for all the connections (as each connection will be stored in two tables). It also means I have to make sure connection information is kept in sync in both places. This is obviously not ideal but it does mean that when I load a user table, I only need to load one 'connection' table and have all the information I need. This also presents a separate problem, that of connection object creation. Since each user table has a list of all connections, there are two opportunities for a connection object to be made. However, connections objects (designed to facilitate communication between records) should only be created once. This means I'll have to devise a common caching/factory object to make sure only one connection object is made per connection. Does anybody have any ideas of a better way to do this? Once I've committed to a particular design pattern I'm pretty much stuck with it, so I want to make sure I've come up with the best one possible.

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• Effective backup and archive strategy for database and linked files

  - by busyspin

  I am using Postgres to store a variety of application data for a webapp. Part of the application involves storing and retrieving user uploaded files. I am storing the files in the filesystem with some associated metadata in the database. I am trying to come up with a backup and archive strategy so that I can effectively backup and archive/restore the database and the linked files. Here are the things I want to accomplish. Perform routine backups that can be used for recovery from failures and which include all DB data and the linked files. Ideally, this backup would be done while the app is running. Live backup is certainly possible with a DB but I am not sure how to keep the linked files consistent with the database during the backup process Archive chunks of data as they become "old". These chunks must includes the database data plus any linked files. It should be possible to put the archived data back into production again. It would be ideal if it were easy to determine which ranges of objects were stored in each chunk. Do you have any advice for how to accomplish these goals? If the files were in the database as BLOBS these tasks would be much easier since normal database backup and restore functionality would handle this. I am not sure how to accomplish the same thing when file data is linked to database rows.

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• Strategy for Incremental Datasource fetchings in Excel

  - by user1352530

  I am in an scenario with a table that is refresh by a third app every week. I need to keep accumulating all data in Excel, using an ODBC connection to the database. I am wondering Approach 1: Is there a way to force Excel to append results for every update (this update would be triggered according to a parameter that indicates week)? I tried to define the table for which the connection loads using a dynamic reference but once is anchored first time, table position is never redefined Approach 2: Use an ETL to accumulate all weekly results into a staging table and then connect Excel to it in real time. But, I would need a mechanism for caching old data, as I cannot grow exponentially the time Excel opens. Imagine after 10 years, Excel would need to update at opening 10 years fo data before showing it. Is there a way to store already fetched data and increment it at real time (when book is opened) by selecting new data (with a query/filter of something) Thanks EDIT: Maybe it's better to ask it that way: What is the optimal strategy for a table that keeps growing and needs to be read in real time by Excel? I just don't want to fetch absolutely all data after some months...

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• Design Patterns for Coordinating Change Event Listeners

  - by mkraken

  I've been working with the Observer pattern in JavaScript using various popular libraries for a number of years (YUI & jQuery). It's often that I need to observe a set of property value changes (e.g. respond only when 2 or more specific values change). Is there a elegant way to 'subscribe' the handler so that it is only called one time? Is there something I'm missing or doing wrong in my design?

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