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• Designing An ACL Based Permission System

  - by ryanzec

  I am trying to create a permissions system where everything is going to be stored in MySQL (or some database) and pulled using PHP for a project management system I am building.  I am right now trying to do it is an ACL kind of way.  There are a number key features I want to be able to support: 1.  Being able to assign permissions without being tied to a specific object. The reason for this is that I want to be able to selectively show/hide elements of the UI based on permissions at a point where I am not directly looking at a domain object instance.  For instance, a button to create a new project should only should only be shown to users that have the pm.project.create permission but obviously you can assign a create permission to an domain object instance (as it is already created). 2.  Not have to assign permissions for every single object. Obviously creating permissions entries for every single object (projects, tickets, comments, etc…) would become a nightmare to maintain so I want to have some level of permission inheritance. *3.  Be able to filter queries based on permissions. This would be a really nice to have but I am not sure if it is possible.  What I mean by this is say I have a page that list all projects.  I want the query that pulls all projects to incorporate the ACL so that it would not show projects that the current user does not have pm.project.read access to.  This would have to be incorporated into the main query as if it is a process that is done after that main query (which I know I could do) certain features like pagination become much more difficult. Right now this is my basic design for the tables: AclEntities id - the primary key key - the unique identifier for the domain object (usually the primary key of that object) parentId - the parent of the domain object (like the project object if this was a ticket object) aclDomainObjectId - metadata about the domain object AclDomainObjects id - primary key title - simple string to unique identify the domain object(ie. project, ticket, comment, etc…) fullyQualifiedClassName - the fully qualified class name for use in code (I am using namespaces) There would also be tables mapping AclEntities to Users and UserGroups. I also have this interface that all acl entity based object have to implement: IAclEntity getAclKey() - to the the unique key for this specific instance of the acl domain object (generally return the primary key or a concatenated string of a composite primary key) getAclTitle() - to get the unique title for the domain object (generally just returning a static string) getAclDisplayString() - get the string that represents this entity (generally one or more field on the object) getAclParentEntity() - get the parent acl entity object (or null if no parent) getAclEntity() - get the acl enitty object for this instance of the domain object (or null if one has not been created yet) hasPermission($permissionString, $user = null) - whether or not the user has the permission for this instance of the domain object static getFromAclEntityId($aclEntityId) - get a specific instance of the domain object from an acl entity id. Do any of these features I am looking for seems hard to support or are just way off base? Am I missing or not taking in account anything in my implementation? Is performance something I should keep in mind?

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• How should I plan the inheritance structure for my game?

  - by Eric Thoma

  I am trying to write a platform shooter in C++ with a really good class structure for robustness. The game itself is secondary; it is the learning process of writing it that is primary. I am implementing an inheritance tree for all of the objects in my game, but I find myself unsure on some decisions. One specific issue that it bugging me is this: I have an Actor that is simply defined as anything in the game world. Under Actor is Character. Both of these classes are abstract. Under Character is the Philosopher, who is the main character that the user commands. Also under Character is NPC, which uses an AI module with stock routines for friendly, enemy and (maybe) neutral alignments. So under NPC I want to have three subclasses: FriendlyNPC, EnemyNPC and NeutralNPC. These classes are not abstract, and will often be subclassed in order to make different types of NPC's, like Engineer, Scientist and the most evil Programmer. Still, if I want to implement a generic NPC named Kevin, it would nice to be able to put him in without making a new class for him. I could just instantiate a FriendlyNPC and pass some values for the AI machine and for the dialogue; that would be ideal. But what if Kevin is the one benevolent Programmer in the whole world? Now we must make a class for him (but what should it be called?). Now we have a character that should inherit from Programmer (as Kevin has all the same abilities but just uses the friendly AI functions) but also should inherit from FriendlyNPC. Programmer and FriendlyNPC branched away from each other on the inheritance tree, so inheriting from both of them would have conflicts, because some of the same functions have been implemented in different ways on the two of them. 1) Is there a better way to order these classes to avoid these conflicts? Having three subclasses; Friendly, Enemy and Neutral; from each type of NPC; Engineer, Scientist, and Programmer; would amount to a huge number of classes. I would share specific implementation details, but I am writing the game slowly, piece by piece, and so I haven't implemented past Character yet. 2) Is there a place where I can learn these programming paradigms? I am already trying to take advantage of some good design patterns, like MVC architecture and Mediator objects. The whole point of this project is to write something in good style. It is difficult to tell what should become a subclass and what should become a state (i.e. Friendly boolean v. Friendly class). Having many states slows down code with if statements and makes classes long and unwieldy. On the other hand, having a class for everything isn't practical. 3) Are there good rules of thumb or resources to learn more about this? 4) Finally, where does templating come in to this? How should I coordinate templates into my class structure? I have never actually taken advantage of templating honestly, but I hear that it increases modularity, which means good code.

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• Would this be a good web application architecture?

  - by Gustav Bertram

  My problem Our MVC based framework does not allow us to cache only part of our output. Ideally we want to cahce static and semi-static bits, and run dynamic bits. In addition, we need to consider data caching that reacts to database changes. My idea The concept I came up with was to represent a page as a tree of XML fragment objects. (I say XML, but I mean XHTML). Some of the fragments are dynamic, and can pull their data directly from models or other sources, but most of the fragments are static scaffolding. If a subtree of fragments is completely static, then I imagine that they could unfold into pure XML that would then be cached as the text representation of their parent element. This process would ideally continue until we are left with a root element that contains all of the static XML, and has a couple of dynamic XML fragments that are resolved and attached to the relevant nodes of the XML tree just before the page is displayed. In addition to separating content into dynamic and static fragments, some fragments could be dynamic and cached. A simple expiry time which propagates up through the XML fragment tree would indicate that a specific fragment should periodically be refreshed. A newspaper section or front page does not need to be updated each second. Minutes or sometimes even longer is sufficient. Other fragments would be dynamic and uncached. Typically too many articles are viewed for them to be cached - the cache would overflow. Some individual articles may be cached if they are extremely popular. Functional notes The folding mechanism could be to be smart enough to judge when it would be more profitable to fold a dynamic cached fragment and propagate the expiry date to the parent fragment, or to keep it separate and simple attach to the XML tree when resolving the page. If some dynamic cached fragments are associated to database objects through mechanisms like a globally unique content id, then changes to the database could trigger changes to the output cache. If fragments store the identifiers of parent fragments, then they could trigger a refolding process that would then include the updated data. A set of pure XML with an ordered array of fragment objects (that each store the identifying information of the node to which they should be attached), can be resolved in a fairly simple way by walking the XML tree, and merging the data from the fragments. Because it is not necessary to parse and construct the entire tree in memory before attaching nodes, processing should be fairly fast. The identifiers of each fragment would be a combination of relevant identity data and the type of fragment object. Cached parent fragments would contain references to these identifiers, in order to then either pull them from the fragment cache, or to run their code. The controller's responsibility is reduced to making changes to the database, and telling the root XML fragment object to render itself. The Question My question has two parts: Is this a good design? Are there any obvious flaws I'm missing? Has somebody else thought of this before? References? Is there an existing alternative that I should consider? A cool templating engine maybe?

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• Use a custom value object or a Guid as an entity identifier in a distributed system?

  - by Kazark

  tl;dr I've been told that in domain-driven design, an identifier for an entity could be a custom value object, i.e. something other than Guid, string, int, etc. Can this really be advisable in a distributed system? Long version I will invent an situation analogous to the one I am currently facing. Say I have a distributed system in which a central concept is an egg. The system allows you to order eggs and see spending reports and inventory-centric data such as quantity on hand, usage, valuation and what have you. There area variety of services backing these behaviors. And say there is also another app which allows you to compose recipes that link to a particular egg type. Now egg type is broken down by the species—ostrich, goose, duck, chicken, quail. This is fine and dandy because it means that users don't end up with ostrich eggs when they wanted quail eggs and whatnot. However, we've been getting complaints because jumbo chicken eggs are not even close to equivalent to small ones. The price is different, and they really aren't substitutable in recipes. And here we thought we were doing users a favor by not overwhelming them with too many options. Currently each of the services (say, OrderSubmitter, EggTypeDefiner, SpendingReportsGenerator, InventoryTracker, RecipeCreator, RecipeTracker, or whatever) are identifying egg types with an industry-standard integer representation the species (let's call it speciesCode). We realize we've goofed up because this change could effect every service. There are two basic proposed solutions: Use a predefined identifier type like Guid as the eggTypeID throughout all the services, but make EggTypeDefiner the only service that knows that this maps to a speciesCode and eggSizeCode (and potentially to an isOrganic flag in the future, or whatever). Use an EggTypeID value object which is a combination of speciesCode and eggSizeCode in every service. I've proposed the first solution because I'm hoping it better encapsulates the definition of what an egg type is in the EggTypeDefiner and will be more resilient to changes, say if some people now want to differentiate eggs by whether or not they are "organic". The second solution is being suggested by some people who understand DDD better than I do in the hopes that less enrichment and lookup will be necessary that way, with the justification that in DDD using a value object as an ID is fine. Also, they are saying that EggTypeDefiner is not a domain and EggType is not an entity and as such should not have a Guid for an ID. However, I'm not sure the second solution is viable. This "value object" is going to have to be serialized into JSON and URLs for GET requests and used with a variety of technologies (C#, JavaScript...) which breaks encapsulation and thus removes any behavior of the identifier value object (is either of the fields optional? etc.) Is this a case where we want to avoid something that would normally be fine in DDD because we are trying to do DDD in a distributed fashion? Summary Can it be a good idea to use a custom value object as an identifier in a distributed system (solution #2)?

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• Is my class structure good enough?

  - by Rivten

  So I wanted to try out this challenge on reddit which is mostly about how you structure your data the best you can. I decided to challenge my C++ skills. Here's how I planned this. First, there's the Game class. It deals with time and is the only class main has access to. A game has a Forest. For now, this class does not have a lot of things, only a size and a Factory. Will be put in better use when it will come to SDL-stuff I guess A Factory is the thing that deals with the Game Objects (a.k.a. Trees, Lumberjack and Bears). It has a vector of all GameObjects and a queue of Events which will be managed at the end of one month. A GameObject is an abstract class which can be updated and which can notify the Event Listener The EventListener is a class which handles all the Events of a simulation. It can recieve events from a Game Object and notify the Factory if needed, the latter will manage correctly the event. So, the Tree, Lumberjack and Bear classes all inherits from GameObject. And Sapling and Elder Tree inherits from Tree. Finally, an Event is defined by an event_type enumeration (LUMBERJACK_MAWED, SAPPLING_EVOLUTION, ...) and an event_protagonists union (a GameObject or a pair of GameObject (who killed who ?)). I was quite happy at first with this because it seems quite logic and flexible. But I ended up questionning this structure. Here's why : I dislike the fact that a GameObject need to know about the Factory. Indeed, when a Bear moves somewhere, it needs to know if there's a Lumberjack ! Or it is the Factory which handles places and objects. It would be great if a GameObject could only interact with the EventListener... or maybe it's not that much of a big deal. Wouldn't it be better if I separate the Factory in three vectors ? One for each kind of GameObject. The idea would be to optimize research. If I'm looking do delete a dead lumberjack, I would only have to look in one shorter vector rather than a very long vector. Another problem arises when I want to know if there is any particular object in a given case because I have to look for all the gameObjects and see if they are at the given case. I would tend to think that the other idea would be to use a matrix but then the issue would be that I would have empty cases (and therefore unused space). I don't really know if Sapling and Elder Tree should inherit from Tree. Indeed, a Sapling is a Tree but what about its evolution ? Should I just delete the sapling and say to the factory to create a new Tree at the exact same place ? It doesn't seem natural to me to do so. How could I improve this ? Is the design of an Event quite good ? I've never used unions before in C++ but I didn't have any other ideas about what to use. Well, I hope I have been clear enough. Thank you for taking the time to help me !

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• Best way to load application settings

  - by enzom83

  A simple way to keep the settings of a Java application is represented by a text file with ".properties" extension containing the identifier of each setting associated with a specific value (this value may be a number, string, date, etc..). C# uses a similar approach, but the text file must be named "App.config". In both cases, in source code you must initialize a specific class for reading settings: this class has a method that returns the value (as string) associated with the specified setting identifier. // Java example Properties config = new Properties(); config.load(...); String valueStr = config.getProperty("listening-port"); // ... // C# example NameValueCollection setting = ConfigurationManager.AppSettings; string valueStr = setting["listening-port"]; // ... In both cases we should parse strings loaded from the configuration file and assign the ??converted values to the related typed objects (parsing errors could occur during this phase). After the parsing step, we must check that the setting values ??belong to a specific domain of validity: for example, the maximum size of a queue should be a positive value, some values ??may be related (example: min < max), and so on. Suppose that the application should load the settings as soon as it starts: in other words, the first operation performed by the application is to load the settings. Any invalid values for the settings ??must be replaced automatically with default values??: if this happens to a group of related settings, those settings are all set with default values. The easiest way to perform these operations is to create a method that first parses all the settings, then checks the loaded values ??and finally sets any default values??. However maintenance is difficult if you use this approach: as the number of settings increases while developing the application, it becomes increasingly difficult to update the code. In order to solve this problem, I had thought of using the Template Method pattern, as follows. public abstract class Setting { protected abstract bool TryParseValues(); protected abstract bool CheckValues(); public abstract void SetDefaultValues(); /// <summary> /// Template Method /// </summary> public bool TrySetValuesOrDefault() { if (!TryParseValues() || !CheckValues()) { // parsing error or domain error SetDefaultValues(); return false; } return true; } } public class RangeSetting : Setting { private string minStr, maxStr; private byte min, max; public RangeSetting(string minStr, maxStr) { this.minStr = minStr; this.maxStr = maxStr; } protected override bool TryParseValues() { return (byte.TryParse(minStr, out min) && byte.TryParse(maxStr, out max)); } protected override bool CheckValues() { return (0 < min && min < max); } public override void SetDefaultValues() { min = 5; max = 10; } } The problem is that in this way we need to create a new class for each setting, even for a single value. Are there other solutions to this kind of problem? In summary: Easy maintenance: for example, the addition of one or more parameters. Extensibility: a first version of the application could read a single configuration file, but later versions may give the possibility of a multi-user setup (admin sets up a basic configuration, users can set only certain settings, etc..). Object oriented design.

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• Writing a method to 'transform' an immutable object: how should I approach this?

  - by Prog

  (While this question has to do with a concrete coding dilemma, it's mostly about what's the best way to design a function.) I'm writing a method that should take two Color objects, and gradually transform the first Color into the second one, creating an animation. The method will be in a utility class. My problem is that Color is an immutable object. That means that I can't do color.setRGB or color.setBlue inside a loop in the method. What I can do, is instantiate a new Color and return it from the method. But then I won't be able to gradually change the color. So I thought of three possible solutions: 1- The client code includes the method call inside a loop. For example: int duration = 1500; // duration of the animation in milliseconds int steps = 20; // how many 'cycles' the animation will take for(int i=0; i<steps; i++) color = transformColor(color, targetColor, duration, steps); And the method would look like this: Color transformColor(Color original, Color target, int duration, int steps){ int redDiff = target.getRed() - original.getRed(); int redAddition = redDiff / steps; int newRed = original.getRed() + redAddition; // same for green and blue .. Thread.sleep(duration / STEPS); // exception handling omitted return new Color(newRed, newGreen, newBlue); } The disadvantage of this approach is that the client code has to "do part of the method's job" and include a for loop. The method doesn't do it's work entirely on it's own, which I don't like. 2- Make a mutable Color subclass with methods such as setRed, and pass objects of this class into transformColor. Then it could look something like this: void transformColor(MutableColor original, Color target, int duration){ final int STEPS = 20; int redDiff = target.getRed() - original.getRed(); int redAddition = redDiff / steps; int newRed = original.getRed() + redAddition; // same for green and blue .. for(int i=0; i<STEPS; i++){ original.setRed(original.getRed() + redAddition); // same for green and blue .. Thread.sleep(duration / STEPS); // exception handling omitted } } Then the calling code would usually look something like this: // The method will usually transform colors of JComponents JComponent someComponent = ... ; // setting the Color in JComponent to be a MutableColor Color mutableColor = new MutableColor(someComponent.getForeground()); someComponent.setForeground(mutableColor); // later, transforming the Color in the JComponent transformColor((MutableColor)someComponent.getForeground(), new Color(200,100,150), 2000); The disadvantage is - the need to create a new class MutableColor, and also the need to do casting. 3- Pass into the method the actual mutable object that holds the color. Then the method could do object.setColor or similar every iteration of the loop. Two disadvantages: A- Not so elegant. Passing in the object that holds the color just to transform the color feels unnatural. B- While most of the time this method will be used to transform colors inside JComponent objects, other kinds of objects may have colors too. So the method would need to be overloaded to receive other types, or receive Objects and have instanceof checks inside.. Not optimal. Right now I think I like solution #2 the most, than solution #1 and solution #3 the least. However I'd like to hear your opinions and suggestions regarding this.

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• Why is 0 false?

  - by Morwenn

  This question may sound dumb, but why does 0 evaluates to false and any other [integer] value to true is most of programming languages? String comparison Since the question seems a little bit too simple, I will explain myself a little bit more: first of all, it may seem evident to any programmer, but why wouldn't there be a programming language - there may actually be, but not any I used - where 0 evaluates to true and all the other [integer] values to false? That one remark may seem random, but I have a few examples where it may have been a good idea. First of all, let's take the example of strings three-way comparison, I will take C's strcmp as example: any programmer trying C as his first language may be tempted to write the following code: if (strcmp(str1, str2)) { // Do something... } Since strcmp returns 0 which evaluates to false when the strings are equal, what the beginning programmer tried to do fails miserably and he generally does not understand why at first. Had 0 evaluated to true instead, this function could have been used in its most simple expression - the one above - when comparing for equality, and the proper checks for -1 and 1 would have been done only when needed. We would have considered the return type as bool (in our minds I mean) most of the time. Moreover, let's introduce a new type, sign, that just takes values -1, 0 and 1. That can be pretty handy. Imagine there is a spaceship operator in C++ and we want it for std::string (well, there already is the compare function, but spaceship operator is more fun). The declaration would currently be the following one: sign operator<=>(const std::string& lhs, const std::string& rhs); Had 0 been evaluated to true, the spaceship operator wouldn't even exist, and we could have declared operator== that way: sign operator==(const std::string& lhs, const std::string& rhs); This operator== would have handled three-way comparison at once, and could still be used to perform the following check while still being able to check which string is lexicographically superior to the other when needed: if (str1 == str2) { // Do something... } Old errors handling We now have exceptions, so this part only applies to the old languages where no such thing exist (C for example). If we look at C's standard library (and POSIX one too), we can see for sure that maaaaany functions return 0 when successful and any integer otherwise. I have sadly seen some people do this kind of things: #define TRUE 0 // ... if (some_function() == TRUE) { // Here, TRUE would mean success... // Do something } If we think about how we think in programming, we often have the following reasoning pattern: Do something Did it work? Yes -> That's ok, one case to handle No -> Why? Many cases to handle If we think about it again, it would have made sense to put the only neutral value, 0, to yes (and that's how C's functions work), while all the other values can be there to solve the many cases of the no. However, in all the programming languages I know (except maybe some experimental esotheric languages), that yes evaluates to false in an if condition, while all the no cases evaluate to true. There are many situations when "it works" represents one case while "it does not work" represents many probable causes. If we think about it that way, having 0 evaluate to true and the rest to false would have made much more sense. Conclusion My conclusion is essentially my original question: why did we design languages where 0 is false and the other values are true, taking in account my few examples above and maybe some more I did not think of? Follow-up: It's nice to see there are many answers with many ideas and as many possible reasons for it to be like that. I love how passionate you seem to be about it. I originaly asked this question out of boredom, but since you seem so passionate, I decided to go a little further and ask about the rationale behind the Boolean choice for 0 and 1 on Math.SE :)

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• Best Method For Evaluating Existing Software or New Software

  How many of us have been faced with having to decide on an off-the-self or a custom built component, application, or solution to integrate in to an existing system or to be the core foundation of a new system? What is the best method for evaluating existing software or new software still in the design phase? One of the industry preferred methodologies to use is the Active Reviews for Intermediate Designs (ARID) evaluation process.  ARID is a hybrid mixture of the Active Design Review (ADR) methodology and the Architectural Tradeoff Analysis Method (ATAM). So what is ARID? ARD’s main goal is to ensure quality, detailed designs in software. One way in which it does this is by empowering reviewers by assigning generic open ended survey questions. This approach attempts to remove the possibility for allowing the standard answers such as “Yes” or “No”. The ADR process ignores the “Yes”/”No” questions due to the fact that they can be leading based on how the question is asked. Additionally these questions tend to receive less thought in comparison to more open ended questions. Common Active Design Review Questions What possible exceptions can occur in this component, application, or solution? How should exceptions be handled in this component, application, or solution? Where should exceptions be handled in this component, application, or solution? How should the component, application, or solution flow based on the design? What is the maximum execution time for every component, application, or solution? What environments can this component, application, or solution? What data dependencies does this component, application, or solution have? What kind of data does this component, application, or solution require? Ok, now I know what ARID is, how can I apply? Let’s imagine that your organization is going to purchase an off-the-shelf (OTS) solution for its customer-relationship management software. What process would we use to ensure that the correct purchase is made? If we use ARID, then we will have a series of 9 steps broken up by 2 phases in order to ensure that the correct OTS solution is purchases. Phase 1 Identify the Reviewers Prepare the Design Briefing Prepare the Seed Scenarios Prepare the Materials When identifying reviewers for a design it is preferred that they be pulled from a candidate pool comprised of developers that are going to implement the design. The believe is that developers actually implementing the design will have more a vested interest in ensuring that the design is correct prior to the start of code. Design debriefing consist of a summary of the design, examples of the design solving real world examples put in to use and should be no longer than two hours typically. The primary goal of this briefing is to adequately summarize the design so that the review members could actually implement the design. In the example of purchasing an OTS product I would attempt to review my briefing prior to its distribution with the review facilitator to ensure that nothing was excluded that should have not been. This practice will also allow me to test the length of the briefing to ensure that can be delivered in an appropriate about of time. Seed Scenarios are designed to illustrate conceptualized scenarios when applied with a set of sample data. These scenarios can then be used by the reviewers in the actual evaluation of the software, All materials needed for the evaluation should be prepared ahead of time so that they can be reviewed prior to and during the meeting. Materials Included: Presentation Seed Scenarios Review Agenda Phase 2 Present ARID Present Design Brainstorm and prioritize scenarios Apply scenarios Summarize Prior to the start of any ARID review meeting the Facilitator should define the remaining steps of ARID so that all the participants know exactly what they are doing prior to the start of the review process. Once the ARID rules have been laid out, then the lead designer presents an overview of the design which typically takes about two hours. During this time no questions about the design or rational are allowed to be asked by the review panel as a standard, but they are written down for use latter in the process. After the presentation the list of compiled questions is then summarized and sent back to the lead designer as areas that need to be addressed further. In the example of purchasing an OTS product issues could arise regarding security, the implementation needed or even if this is this the correct product to solve the needed solution. After the Design presentation a brainstorming and prioritize scenarios process begins by reducing the seed scenarios down to just the highest priority scenarios.  These will then be used to test the design for suitability. Once the selected scenarios have been defined the reviewers apply the examples provided in the presentation to the scenarios. The intended output of this process is to provide code or pseudo code that makes use of the examples provided while solving the selected seed scenarios. As a standard rule, the designers of the systems are not allowed to help the review board unless they all become stuck. When this occurs it is documented and along with the reason why the designer needed to help the review panel back on track. Once all of the scenarios have been completed the review facilitator reviews with the group issues that arise during the process. Then the reviewers will be polled as to efficacy of the review experience. References: Clements, Paul., Kazman, Rick., Klien, Mark. (2002). Evaluating Software Architectures: Methods and Case Studies Indianapolis, IN: Addison-Wesley

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• High Availability for IaaS, PaaS and SaaS in the Cloud

  - by BuckWoody

  Outages, natural disasters and unforeseen events have proved that even in a distributed architecture, you need to plan for High Availability (HA). In this entry I'll explain a few considerations for HA within Infrastructure-as-a-Service (IaaS), Platform-as-a-Service (PaaS) and Software-as-a-Service (SaaS). In a separate post I'll talk more about Disaster Recovery (DR), since each paradigm has a different way to handle that. Planning for HA in IaaS IaaS involves Virtual Machines - so in effect, an HA strategy here takes on many of the same characteristics as it would on-premises. The primary difference is that the vendor controls the hardware, so you need to verify what they do for things like local redundancy and so on from the hardware perspective. As far as what you can control and plan for, the primary factors fall into three areas: multiple instances, geographical dispersion and task-switching. In almost every cloud vendor I've studied, to ensure your application will be protected by any level of HA, you need to have at least two of the Instances (VM's) running. This makes sense, but you might assume that the vendor just takes care of that for you - they don't. If a single VM goes down (for whatever reason) then the access to it is lost. Depending on multiple factors, you might be able to recover the data, but you should assume that you can't. You should keep a sync to another location (perhaps the vendor's storage system in another geographic datacenter or to a local location) to ensure you can continue to serve your clients. You'll also need to host the same VM's in another geographical location. Everything from a vendor outage to a network path problem could prevent your users from reaching the system, so you need to have multiple locations to handle this. This means that you'll have to figure out how to manage state between the geo's. If the system goes down in the middle of a transaction, you need to figure out what part of the process the system was in, and then re-create or transfer that state to the second set of systems. If you didn't write the software yourself, this is non-trivial. You'll also need a manual or automatic process to detect the failure and re-route the traffic to your secondary location. You could flip a DNS entry (if your application can tolerate that) or invoke another process to alias the first system to the second, such as load-balancing and so on. There are many options, but all of them involve coding the state into the application layer. If you've simply moved a state-ful application to VM's, you may not be able to easily implement an HA solution. Planning for HA in PaaS Implementing HA in PaaS is a bit simpler, since it's built on the concept of stateless applications deployment. Once again, you need at least two copies of each element in the solution (web roles, worker roles, etc.) to remain available in a single datacenter. Also, you need to deploy the application again in a separate geo, but the advantage here is that you could work out a "shared storage" model such that state is auto-balanced across the world. In fact, you don't have to maintain a "DR" site, the alternate location can be live and serving clients, and only take on extra load if the other site is not available. In Windows Azure, you can use the Traffic Manager service top route the requests as a type of auto balancer. Even with these benefits, I recommend a second backup of storage in another geographic location. Storage is inexpensive; and that second copy can be used for not only HA but DR. Planning for HA in SaaS In Software-as-a-Service (such as Office 365, or Hadoop in Windows Azure) You have far less control over the HA solution, although you still maintain the responsibility to ensure you have it. Since each SaaS is different, check with the vendor on the solution for HA - and make sure you understand what they do and what you are responsible for. They may have no HA for that solution, or pin it to a particular geo, or perhaps they have a massive HA built in with automatic load balancing (which is often the case).   All of these options (with the exception of SaaS) involve higher costs for the design. Do not sacrifice reliability for cost - that will always cost you more in the end. Build in the redundancy and HA at the very outset of the project - if you try to tack it on later in the process the business will push back and potentially not implement HA. References: http://www.bing.com/search?q=windows+azure+High+Availability  (each type of implementation is different, so I'm routing you to a search on the topic - look for the "Patterns and Practices" results for the area in Azure you're interested in)

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• How can I implement a database TableView like thing in C++?

  - by Industrial-antidepressant

  How can I implement a TableView like thing in C++? I want to emulating a tiny relation database like thing in C++. I have data tables, and I want to transform it somehow, so I need a TableView like class. I want filtering, sorting, freely add and remove items and transforming (ex. view as UPPERCASE and so on). The whole thing is inside a GUI application, so datatables and views are attached to a GUI (or HTML or something). So how can I identify an item in the view? How can I signal it when the table is changed? Is there some design pattern for this? Here is a simple table, and a simple data item: #include <string> #include <boost/multi_index_container.hpp> #include <boost/multi_index/member.hpp> #include <boost/multi_index/ordered_index.hpp> #include <boost/multi_index/random_access_index.hpp> using boost::multi_index_container; using namespace boost::multi_index; struct Data { Data() {} int id; std::string name; }; struct row{}; struct id{}; struct name{}; typedef boost::multi_index_container< Data, indexed_by< random_access<tag<row> >, ordered_unique<tag<id>, member<Data, int, &Data::id> >, ordered_unique<tag<name>, member<Data, std::string, &Data::name> > > > TDataTable; class DataTable { public: typedef Data item_type; typedef TDataTable::value_type value_type; typedef TDataTable::const_reference const_reference; typedef TDataTable::index<row>::type TRowIndex; typedef TDataTable::index<id>::type TIdIndex; typedef TDataTable::index<name>::type TNameIndex; typedef TRowIndex::iterator iterator; DataTable() : row_index(rule_table.get<row>()), id_index(rule_table.get<id>()), name_index(rule_table.get<name>()), row_index_writeable(rule_table.get<row>()) { } TDataTable::const_reference operator[](TDataTable::size_type n) const { return rule_table[n]; } std::pair<iterator,bool> push_back(const value_type& x) { return row_index_writeable.push_back(x); } iterator erase(iterator position) { return row_index_writeable.erase(position); } bool replace(iterator position,const value_type& x) { return row_index_writeable.replace(position, x); } template<typename InputIterator> void rearrange(InputIterator first) { return row_index_writeable.rearrange(first); } void print_table() const; unsigned size() const { return row_index.size(); } TDataTable rule_table; const TRowIndex& row_index; const TIdIndex& id_index; const TNameIndex& name_index; private: TRowIndex& row_index_writeable; }; class DataTableView { DataTableView(const DataTable& source_table) {} // How can I implement this? // I want filtering, sorting, signaling upper GUI layer, and sorting, and ... }; int main() { Data data1; data1.id = 1; data1.name = "name1"; Data data2; data2.id = 2; data2.name = "name2"; DataTable table; table.push_back(data1); DataTable::iterator it1 = table.row_index.iterator_to(table[0]); table.erase(it1); table.push_back(data1); Data new_data(table[0]); new_data.name = "new_name"; table.replace(table.row_index.iterator_to(table[0]), new_data); for (unsigned i = 0; i < table.size(); ++i) std::cout << table[i].name << std::endl; #if 0 // using scenarios: DataTableView table_view(table); table_view.fill_from_source(); // synchronization with source table_view.remove(data_item1); // remove item from view table_view.add(data_item2); // add item from source table table_view.filter(filterfunc); // filtering table_view.sort(sortfunc); // sorting // modifying from source_able, hot to signal the table_view? // FYI: Table view is atteched to a GUI item table.erase(data); table.replace(data); #endif return 0; }

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• Using mocks to set up object even if you will not be mocking any behavior or verifying any interaction with it?

  - by smp7d

  When building a unit test, is it appropriate to use a mocking tool to assist you in setting up an object even if you will not be mocking any behavior or verifying any interaction with that object? Here is a simple example in pseudo-code: //an object we actually want to mock Object someMockedObject = Mock(Object.class); EqualityChecker checker = new EqualityChecker(someMockedObject); //an object we are mocking only to avoid figuring out how to instantiate or //tying ourselves to some constructor that may be removed in the future ComplicatedObject someObjectThatIsHardToInstantiate = Mock(ComplicatedObject.class); //set the expectation on the mock When(someMockedObject).equals(someObjectThatIsHardToInstantiate).return(false); Assert(equalityChecker.check(someObjectThatIsHardToInstantiate)).isFalse(); //verify that the mock was interacted with properly Verify(someMockedObject).equals(someObjectThatIsHardToInstantiate).oneTime(); Is it appropriate to mock ComplicatedObject in this scenario?

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• C#. Struct design. Why 16 byte is recommended size?

  - by maxima120

  I read Cwalina book (recommendations on development and design of .NET apps). He says that good designed struct has to be less than 16 bytes in size (for performance purpose). My questions is - why exactly is this? And (more important) can I have larger struct with same efficiency if I run my .NET 3.5 (soon to be .NET 4.0) 64-bit application on i7 under Win7 x64 (is this limitation CPU / OS based)? Just to stress again - I need as efficient struct as it is possible. I try to keep it in stack all the time, the application is heavily multi-threaded and runs on sub-millisecond intervals, the current size of the struct is 64 byte.

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• NetFx40_LegacySecurityPolicy in design-time mode

  - by Ilya

  Hi, Is there any way to make legacy design-time code execute with NetFx40_LegacySecurityPolicy switched on? More spicificaly, is there any way to make DevExpress 8.2 winforms designer work in VisualStudio 2010? I got errors due to this issue and found no help about design-time mode, just about run-time: <runtime> <NetFx40_LegacySecurityPolicy enabled="true"/> </runtime> How should I fix problems with winforms designer?

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• beautiful win forms application design in c#

  - by Nano HE

  Hi. How to design a beautiful win forms UI.(a little like MSN message client) I googled and couldn't find the way to start my befault win forms learning. Do i missed some C# win form design tech? Must i need start .net 3.5 study? .net 2.0 vs2005 used.

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• network design to segregate public and staff

  - by barb

  My current setup has: a pfsense firewall with 4 NICs and potential for a 5th 1 48 port 3com switch, 1 24 port HP switch, willing to purchase more subnet 1) edge (Windows Server 2003 for vpn through routing and remote access) and subnet 2) LAN with one WS2003 domain controller/dns/wins etc., one WS2008 file server, one WS2003 running Vipre anti-virus and Time Limit Manager which controls client computer use, and about 50 pcs I am looking for a network design for separating clients and staff. I could do two totally isolated subnets, but I'm wondering if there is anything in between so that staff and clients could share some resources such as printers and anti-virus servers, staff could access client resources, but not vice versa. I guess what I'm asking is can you configure subnets and/or vlans like this: 1)edge for vpn 2)services available to all other internal networks 3)staff which can access services and clients 4)clients which can access services but not staff By access/non-access, I mean stronger separation than domain usernames and passwords.

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• Improving as a coder with respect to design.

  - by dmarakaki

  As a soon-to-be computer science graduate, I have to come realization that I have a long way to go when it comes to the overall design of an application. After spending many semesters of programming from the hip I have come to appreciate the mulling over the needs of an application before diving head first into the coding portion. My question is to the intermediate and expert programmers, how can I improve in the area of the design phase of development?

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• Cancel table design change in SQL Server 2000

  - by Bryce Wagner

  In SQL Server Enterprise Manager and change one of the columns and save it, it will create a table with the new definition, and copy all the data to that new table, and then delete the old table when it's done. But if your table is large (let's say on the order of 100GB), it can take a long time to do this. Even worse, if you don't have sufficient disk space, it doesn't notice ahead of time, and it will spend a long time trying to copy the table, run out of space, and then decide to abort the process. We have other ways to copy the data in smaller chunks, but those require significantly more manual intervention, so it's usually easier to just let Enterprise Manager figure it out, as long as there's enough disk space. So for a long running "Design Table" save like this, is there any way to cancel once it's started? Or do you just have to wait for it to fail?

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• Remote site AD design (2003)

  - by Boy Mars

  A remote site has about 25 of our 50-ish employees. They have their own AD domain presently (2003) but I want to look at getting them onto the same global domain for ease of access/administration. The remote site has a VPN link but line speeds are very poor. I am already aware of tools like ADMT and have done a few migrations in the past (NT/2003 domains), but this is the first time I have the luxury of designing how this domain is organised. So I'm looking for tips on good AD design; would a remote site be better served as a sub-domain? would this reduce traffic? I am only currently looking at 2003 since only existing machine will be used.

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• design a large scale network for an organization

  - by Essam

  i want to design a large scale network for an organization with HQ and two branches. i want to use a class A subnet. if i am using the network address 30.0.0.0 for the whole organization how can it be different from another organization company or whatever which is using the same address in another country? now i have the three locations for this organization,so i need 5 subnets [one for the HQ,two for branch A and branch B , one for connecting A to HQ and one for connecting branch B with HQ since i will use central DHCP server at the HQ,is that (number of subnetting) right? is it advisable to use class A or class B for this organization it term of address that will be wasted (let's say it is a university with two branches in two different states)?!

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• UML or design tools for websites

  - by Malfist

  What is a good tool to design the implementation of websites? I typically use UMl to design applications, but I feel that does not apply well to websites, specifically the heavy emphasis on UI that websites require. What would be a good tool to use to plan a webpage?

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• Online Collaborative Schema Design (leverage google docs?)

  - by AK

  I'm looking for an online, collaborative schema designer. It's important that it can handle revisions (history of changes). This looks cool, and I could host it on a server - but doesn't look like it would handle multi-user: http://ondras.zarovi.cz/sql/demo/ Currently we're doing a lot of design collaboration on google docs/spreadsheets. Has anyone had any success using google spreadsheet for schema design? Even if there were just a gadget for drawing lines/connections, I might give Google Docs a shot.

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• How is architectural design done in an agile environment?

  - by B?????

  I have read Principles for the Agile Architect, where they defined next principles : Principle #1 The teams that code the system design the system. Principle #2 Build the simplest architecture that can possibly work. Principle #3 When in doubt, code it out. Principle #4 They build it, they test it. Principle #5 The bigger the system, the longer the runway. Principle #6 System architecture is a role collaboration. Principle #7 There is no monopoly on innovation. The paper says that most of the architecture design is done during the coding phase, and only system design before that. That is fine. So, how is the system design done? Using UML? Or a document that defines interfaces and major blocks? Maybe something else?

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• Passing a Collection of Java Beans as DataSource to Jasper, How to design this in ireports

  - by Vaishak Suresh

  I need to design a report, that displays the data from a collection(Say List). This list contains multiple POJOs. The POJOs are populated by the data access layer of the application. How do I design a report template for this requirement in iReports?

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• How do we provide valid time estimates during Sprint Planning without doing "too much" design?

  - by Michael Edenfield

  My team is getting up to speed with Scrum, but most of us are more familiar with non-agile or "pseudo-"agile methodologies. The part that is the biggest hurdle for us is running an efficient Sprint Planning meeting where we break our backlog items into tasks, and estimate hours. (I'm using the terminology from the VS2010 Scrum Template; apologies if I use the wrong word somewhere.) When we try to figure out how long a task is going to take, we often fall into the trap of designing the feature at the code level -- table layout, interfaces, etc -- in order to figure out how long that's going to take. I'm pretty sure this is not the appropriate place to be doing that kind of design. We should be scheduling tasks for these design meetings during the sprint. However, we are having trouble figuring out how else to come up with meaningful estimates for the tasks. Are there any practical habits/techniques/etc. for making a judgement call about how long a feature is going to take, without knowing how you plan to implement it? If our time estimates are going to change significantly once the design has been completed, how can we properly budget our Sprint backlog ahead of time? EDIT: Just to clarify, since some of the comments/answers are very valid but I think addressing the wrong question. We know that what we're doing is not right, and that we should be building time into the sprint for this design. Conceptually all of the developers understand that. We also also bringing in a team member with Scrum experience to keep us on track if we start going off into the weeds. The problem is that, without going through this design process, we are finding it difficult to provide concrete time estimates for anything. We are constantly saying things like "well if we design it this way it might take 8 hours but if we end up having to do this other way instead that will take about 32 but it might not be as bad once we start trying to write it...". I also assume that this process will get better once we have some historical velocity to work from, but many of the technologies and architectural patterns we are using are new to us. But if potentially-wildly-wrong estimates are just a natural part of adapting this process then we will just need to recondition ourselves to accept that :)

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