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• Implementing the transport layer for a SIP UAC

  - by Jonathan Henson

  I have a somewhat simple, but specific, question about implementing the transport layer for a SIP UAC. Do I expect the response to a request on the same socket that I sent the request on, or do I let the UDP or TCP listener pick up the response and then route it to the correct transaction from there? The RFC does not seem to say anything on the matter. It seems that especially using UDP, which is connection-less, that I should just let the listeners pick up the response, but that seems sort of counter intuitive. Particularly, I have seen plenty of UAC implementations which do not depend on having a Listener in the transport layer. Also, most implementations I have looked at do not have the UAS receiving loop responding on the socket at all. This would tend to indicate that the client should not be expecting a reply on the socket that it sent the request on. For clarification: Suppose my transport layer consists of the following elements: TCPClient (Sends Requests for a UAC via TCP) UDPClient (Sends Requests for a UAC vid UDP) TCPSever (Loop receiving Requests and dispatching to transaction layer via TCP) UDPServer (Loop receiving Requests and dispatching to transaction layer via UDP) Obviously, the *Client sends my Requests. The question is, what receives the Response? The *Client waiting on a recv or recvfrom call on the socket it used to send the request, or the *Server? Conversely, the *Server receives my requests, What sends the Response? The *Client? doesn't this break the roles of each member a bit?

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• Object oriented EDI handling in PHP

  - by Robert van der Linde

  I'm currently starting a new sub project where I will: Retrieve the order information from our mainframe Save the order information to our web-apps' database Send the order as EDI (either D01b or D93a) Receive the order response, despatch advice and invoice messages Do all kinds of fun things with the resulting datasets. However I am struggling with my initial class designs. The order information will be retrieved from the mainframe which will result in a "AOrder" class, this isn't a problem, I am not sure about how to mold this local object into an EDI string. Should I create EDIOrder/EDIOrderResponse/etc classes with matching decorators (EDIOrderD01BDecorator, EDIOrderD93ADecorator)? Do I need builder objects or can I do: // $myOrder is instance of AOrder $myOrder->toEDIOrder(); $decorator = new EDIOrderD01BDecorator($myOrder); $edi = $decorator->getEDIString(); And it'll have to work the other way around as well. Is the following code a good way of handling this problem or should I go about this differently? $ediString = $myEDIMessageBroker->fetch(); $ediOrderResponse = EDIOrderResponse::fromString($ediString); I'm just not so sure about how I should go about designing the classes and interactions between them. Thanks for reading and helping.

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• What good books are out there on program execution models? [on hold]

  - by murungu

  Can anyone out there name a few books that address the topic of program execution models?? I want a book that can answer questions such as... What is the difference between interpreted and compiled languages and what are the performance consequences at runtime?? What is the difference between lazy evaluation, eager evaluation and short circuit evaluation?? Why would one choose to use one evaluation strategy over another?? How do you simulate lazy evaluation in a language that favours eager evaluation??

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• What is required for a scope in an injection framework?

  - by johncarl

  Working with libraries like Seam, Guice and Spring I have become accustomed to dealing with variables within a scope. These libraries give you a handful of scopes and allow you to define your own. This is a very handy pattern for dealing with variable lifecycles and dependency injection. I have been trying to identify where scoping is the proper solution, or where another solution is more appropriate (context variable, singleton, etc). I have found that if the scope lifecycle is not well defined it is very difficult and often failure prone to manage injections in this way. I have searched on this topic but have found little discussion on the pattern. Is there some good articles discussing where to use scoping and what are required/suggested prerequisites for scoping? I interested in both reference discussion or your view on what is required or suggested for a proper scope implementation. Keep in mind that I am referring to scoping as a general idea, this includes things like globally scoped singletons, request or session scoped web variable, conversation scopes, and others. Edit: Some simple background on custom scopes: Google Guice custom scope Some definitions relevant to above: “scoping” - A set of requirements that define what objects get injected at what time. A simple example of this is Thread scope, based on a ThreadLocal. This scope would inject a variable based on what thread instantiated the class. Here's an example of this: “context variable” - A repository passed from one object to another holding relevant variables. Much like scoping this is a more brute force way of accessing variables based on the calling code. Example: methodOne(Context context){ methodTwo(context); } methodTwo(Context context){ ... //same context as method one, if called from method one } “globally scoped singleton” - Following the singleton pattern, there is one object per application instance. This applies to scopes because there is a basic lifecycle to this object: there is only one of these objects instantiated. Here's an example of a JSR330 Singleton scoped object: @Singleton public void SingletonExample{ ... } usage: public class One { @Inject SingeltonExample example1; } public class Two { @Inject SingeltonExample example2; } After instantiation: one.example1 == two.example2 //true;

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• Which data structure you will use to for a witness list?

  - by mateen

  I'm making a game where the plot is a bank robbery. Lots of people witness that robbery. The game will load a list of suspects, while the players (witnesses) will have to identify the suspects of this robbery. The game should load a list of suspects to identify the one as quickly as possible. Admin can add/remove suspects in the lists and two or more lists of suspects can also be merged into one (to show it to the player). The question is which data structure will be suitable to develop the lists?

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• Should I incorporate exit cost into choosing a solution

  - by Mr Happy

  I'm currently choosing between two viable software designs/solutions. Solution 1 is easy to implement, but will lock some data in a propriaty format, and will be hard to change later. Solution 2 is hard to implement, but will be a lot easier to change later on. Should I go YAGNI on this or should I incorporate the exit cost in the decision making? Or asked differently, is the exit cost part of the TCO? I'm thinking of going back to the customer with this to ask wether or not he thinks the exit costs are relevant, but I'd like to know what the community thinks first. P.S. Is exit cost the correct term?

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• Procedural terrains in 3D: what has been done ? Are there common algo and/or theories about it ?

  - by jokoon

  Besides programming, modeling an environment takes a great deal of time. I don't know about the work time involved, for example, in a WoW dungeon level, or other beautiful city-like, future environment, jungles, fantasy, etc, but this kind of work is made from scratch by artists. What are the techniques involved in the TorchLight level randomizer, and does other titles have similarities with this ? Is there a family name for such techniques ?

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• Identifying the best pattern

  - by Daniel Grillo

  I'm developing a software to program a device. I have some commands like Reset, Read_Version, Read_memory, Write_memory, Erase_memory. Reset and Read_Version are fixed. They don't need parameters. Read_memory and Erase_memory need the same parameters that are Length and Address. Write_memory needs Lenght, Address and Data. For each command, I have the same steps in sequence, that are something like this sendCommand, waitForResponse, treatResponse. I'm having difficulty to identify which pattern should I use. Factory, Template Method, Strategy or other pattern.

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• Relationships in a Chen ERD

  - by Nibroc A Rehpotsirhc

  I am working on a Chen ERD to model our organizations merchandise. Our central entity is a Style. We have supplemental entities of Color and Season. I am defining our assortment as the relationship between these three entities, and this relationship itself will have attributes and is defined by the three entities which participate in the mandatory relationship. The rules are; Many Styles can be offered in a Season, and a Style can be offered in many Seasons. Within a Season, a Style can be offered in Many Colors. I then have 2 other entities, one of which I believe is a weak entity, Climate, and the other may be weak, but I am not sure, this being Transaction Channel. I am thinking of these as relationships off of a relationship? Meaning, for a given Style/Color combination offered in a Season, it can be available through 1 or more Transaction Channels. Additionally, within a season, a given Style/Color combination can be intended for 1 or more Climates. Is it valid to have relationships off of relationships? Or does this requirement dictate that I should think of this Style/Color/Season relationship as an entity itself, and define the relationships to Climate and Transaction Channel off of this entity?

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• Relationship between Repository and Unit of Work

  - by NullOrEmpty

  I am going to implement a repository, and I would like to use the UOW pattern since the consumer of the repository could do several operations, and I want to commit them at once. After read several articles about the matter, I still don't get how to relate this two elements, depending on the article it is being done in a way u other. Sometimes the UOW is something internal to the repository: public class Repository { UnitOfWork _uow; public Repository() { _uow = IoC.Get<UnitOfWork>(); } public void Save(Entity e) { _uow.Track(e); } public void SubmittChanges() { SaveInStorage(_uow.GetChanges()); } } And sometimes it is external: public class Repository { public void Save(Entity e, UnitOfWork uow) { uow.Track(e); } public void SubmittChanges(UnitOfWork uow) { SaveInStorage(uow.GetChanges()); } } Other times, is the UOW whom references the Repository public class UnitOfWork { Repository _repository; public UnitOfWork(Repository repository) { _repository = repository; } public void Save(Entity e) { this.Track(e); } public void SubmittChanges() { _repository.Save(this.GetChanges()); } } How are these two elements related? UOW tracks the elements that needs be changed, and repository contains the logic to persist those changes, but... who call who? Does the last make more sense? Also, who manages the connection? If several operations have to be done in the repository, I think using the same connection and even transaction is more sound, so maybe put the connection object inside the UOW and this one inside the repository makes sense as well. Cheers

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• Representing heightmaps, on disk and when drawing

  - by gardian06

  This is a conglomeration question when answering please specify which part you are addressing. I am looking at creating a maze type game that utilizes elevation. I have a few features I would like to have, but am unsure as to some of the implementation. I have done work doing fileIO maze generation (using a key to read the file, and then generate the level based on that file), but I am unsure how to think about this with elevation in the mix. I think height maps might be a good approach, but don't know how to represent them effectively. for a height map which is more beneficial XML(containing h[u,v] data and key definition), CSV (item1 is key reference, item2 is elevation), or another approach that I have not thought of yet? When it comes to placing the elevation values themselves what kind of deltah values are appropriate to have it noticeable at about a 60degree angle while not really effecting gravity driven physics (assuming some effect while moving up/down hill)? I am thinking of maybe going to procedural generation at some point, but am wondering if it is practical to have a procedurally generated grid (wall squares possibly same dimensions as the open space squares), or if designing to a thin wall open spaces is better? this decision will effect the amount of work need on the graphics end for uniform vs. irregular walls. EDIT: Game will be a elevation maze shooter. Levels/maps will be mazes with elevation the player has to negotiate. Elevations will have effects on "combat" vision, and movement.

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• Developing a live video-streaming website

  - by cawecoy

  I'm a computer science student and know a little about some technology to start developing my website, like PHP, RubyOnRails and Python, and MySQL and PostgreSQL for Database. I need to know what are the best (secure, stable, low-price, etc) to get started, based on my business information: My website will be a live video-streaming one, similar to livestream.com We need to provide a secure service for our customers. They need to have a page to create and configure their own Live-Streaming-Videos, get statistics, etc. We work with Wowza Media Server ruuning on an Apache Server In addition, I would like to know some good practices for this kind of website development, as I am new to this. Thanks in advance!

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• Are there any examples of a temporal field/object updater?

  - by Bryan Agee

  The system in question has numerous examples of temporal objects and fields--ones which are a certain variable at a certain point in time. An example of this would be someone's rate of pay--there are different answers depending on when you ask and what the constraints might be; eg, can there ever be more than one of a certain temporal object concurrently, etc. Ideally, there would be an object that handles those constraints when a new state/stateful object is introduced; when a new value is set, it would prevent creating negative ranges and overlaps. Martin Fowler has written some great material on this (such as this description of Temporal Objects) , but what I've found of it tends to be entirely theoretic, with no concrete implementations. PHP is the target language, but examples in any language would be most helpful.

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• Modular enterprise architecture using MVC and Orchard CMS

  - by MrJD

  I'm making a large scale MVC application using Orchard. And I'm going to be separating my logic into modules. I'm also trying to heavily decouple the application for maximum extensibility and testability. I have a rudimentary understanding of IoC, Repository Pattern, Unit of Work pattern and Service Layer pattern. I've made myself a diagram. I'm wondering if it is correct and if there is anything I have missed regarding an extensible application. Note that each module is a separate project. Update So I have many UI modules that use the db module, that's why they've been split up. There are other services the UI modules will use. The UI modules have been split up because they will be made over time, independent of each other.

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• Isn't MVC anti OOP?

  - by m3th0dman

  The main idea behind OOP is to unify data and behavior in a single entity - the object. In procedural programming there is data and separately algorithms modifying the data. In the Model-View-Controller pattern the data and the logic/algorithms are placed in distinct entities, the model and the controller respectively. In an equivalent OOP approach shouldn't the model and the controller be placed in the same logical entity?

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• Why does Clang/LLVM warn me about using default in a switch statement where all enumerated cases are covered?

  - by Thomas Catterall

  Consider the following enum and switch statement: typedef enum { MaskValueUno, MaskValueDos } testingMask; void myFunction(testingMask theMask) { switch theMask { case MaskValueUno: {}// deal with it case MaskValueDos: {}// deal with it default: {} //deal with an unexpected or uninitialized value } }; I'm an Objective-C programmer, but I've written this in pure C for a wider audience. Clang/LLVM 4.1 with -Weverything warns me at the default line: Default label in switch which covers all enumeration values Now, I can sort of see why this is there: in a perfect world, the only values entering in the argument theMask would be in the enum, so no default is necessary. But what if some hack comes along and throws an uninitialized int into my beautiful function? My function will be provided as a drop in library, and I have no control over what could go in there. Using default is a very neat way of handling this. Why do the LLVM gods deem this behaviour unworthy of their infernal device? Should I be preceding this by an if statement to check the argument?

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• Infrastructure to effectively set up experiements and learn from them

  - by David

  Open-org.com is in the early stages of creating our first product, a place on the web, where one can ask lawyers questions at a fraction of their normal costs. An early stage front page can be found here. I got inspired by this video, which is recommended by Jeff Atwood, which talks about getting feedback faster, which is the reason for this question. The problem Needless to say, we want our conversion rates to be as high as possible. Therefore, we want to be able to rapidly set up a new experiment where we change something on the site (like moving an image slightly, rewriting a sentence etc.). We then want to present the modified page to a random subset of the users. After that we will compare the conversion rates of the experiment with another version. I could very well imagine that we want to run 10-100 experiments simultaneously and it would be nice to have features, where experiments that obviously have worse results will be ended before schedule. My question Does infrastructure to support the whole process exist? A short description of our infrastructure... We use EC2 and PHP and have a script to automatically start up new instances with all needed software. Still, starting up a new server for every experiment, seems like a bit of overkill, so I am wondering what other options exist. Btw. If you feel like working for Open-org.com, you can pick a task, and start working, or suggest a new task. All profits are given out to the contributors.

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• Vernon's book Implementing DDD and modeling of underlying concepts

  - by EdvRusj

  Following questions all refer to examples presented in Implementing DDD In article we can see from Figure 6 that both BankingAccount and PayeeAccount represent the same underlying concept of Banking Account BA 1. On page 64 author gives an example of a publishing organization, where the life-cycle of a book goes through several stages ( proposing a book, editorial process, translation of the book ... ) and at each of those stages this book has a different definition. Each stage of the book is defined in a different Bounded Context, but do all these different definitions still represent the same underlying concept of a Book, just like both BankingAccount and PayeeAccount represent the same underlying concept of a BA? 2. a) I understand why User shouldn't exist in Collaboration Context ( CC ), but instead should be defined within Identity and Access Context IAC ( page 65 ). But still, do User ( IAC ), Moderator ( CC ), Author ( CC ),Owner ( CC ) and Participant ( CC ) all represent different aspects of the same underlying concept? b) If yes, then this means that CC contains several model elements ( Moderator, Author, Owner and Participant ), each representing different aspect of the same underlying concept ( just like both BankingAccount and PayeeAccount represent the same underlying concept of a BA ). But isn't this considered a duplication of concepts ( Evan's book, page 339 ), since several model elements in CC represent the same underlying concept? c) If Moderator, Author ... don't represent the same underlying concept, then what underlying concept does each represent? 3. In an e-commerce system, the term Customer has multiple meanings ( page 49 ): When user is browsing the Catalog, Customer has different meaning than when user is placing an Order. But do these two different definitions of a Customer represent the same underlying concept, just like both BankingAccount and PayeeAccount represent the same underlying concept of a BA? thanks

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• Frames per Second and Updates per Second [on hold]

  - by matt murray

  So this is more a general resources question, as I am seeking knowledge on how best to conserve resources in a game (I am writing in Java, and please this is not a thread on what language I should write it in, I have already chosen Java) so that the updates and frames per second could be the highest they could be. In general I am just searching for any articles you may have, any personal experience, anything what so ever that could be of use to a pretty new Java game developer on the subject! Thanks in advance!

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• Is it evil to model JSON responses to classes when they are mostly smilar?

  - by Aybe

  Here's the problem : While implementing a C# wrapper for an online API (Discogs) I've been faced to a dilemma : quite often the responses returned have mostly similar members and while modeling these responses to classes, some questions surfaces on which way to go would be the best. Example : Querying for a 'release' or a 'master' will return an object that contains an array of 'artist', however these 'artists' do not exactly have the same members. Currently I decided to represent these 'artists' as a single 'Artist' class, against having respective 'ReleaseArtist' and 'MasterArtist' classes which soon becomes very confusing even though another problem arises : when a category (master or release) does not return these members, they will be null. Though it might sound confusing as well I find it less confusing than the former situation as I've tackled the problem by simply not showing null members when visualizing these objects. Is this the right approach to follow ? An example of these differences : public class Artist { public List<Alias> Aliases { get; set; } public string DataQuality { get; set; } public List<Image> Images { get; set; } public string Name { get; set; } public List<string> NameVariations { get; set; } public string Profile { get; set; } public string Realname { get; set; } public string ReleasesUrl { get; set; } public string ResourceUrl { get; set; } public string Uri { get; set; } public List<string> Urls { get; set; } } public class ReleaseArtist { public string Join { get; set; } public string Name { get; set; } public string Anv { get; set; } public string Tracks { get; set; } public string Role { get; set; } public string ResourceUrl { get; set; } public int Id { get; set; } }

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• How do I start correctly in building database classes in c#?

  - by e4rthdog

  I am new in C# programming and in OOP. I need to dive into web applications for my company, and I need to do it fast and correct. So even that I know ASP.NET MVC is the way to go, I want to start with some simple applications with ASP.NET Webforms and then advance to MVC logic. Also regarding my db classes: I plan to create common database classes in order to be able to use them either from WinForms or ASP.NET applications. I also know that the way to go is to learn about ORM and EF. BUT I also want to start from where I am feeling comfortable and that is the traditional ADO.NET way. So about my Data Access Layer classes: Should I return my results in datasets or arraylists/lists? Should my methods do their own connect/disconnect from the db, or have separate methods and let the application maintain the connection?

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• My Last "Catch-Up" Post for 2010 Content

  - by KKline

  I did a lot of writing in 2010. Unfortunately, I didn't do a good job of keeping all of that writing equally distributed throughout all of the channels where I'm active. So here are a few more posts from my blog, put on-line during the months of November and December 2010, that I didn't get posted here on SQLBlog.com: 1. It's Time to Upgrade! So many of my customers and many of you, dear readers, are still on SQL Server 2005. Join Kevin Kline , SQL Server MVP and SQL Server Technology Strategist...(read more)

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• Using MVC with a retained mode renderer

  - by David Gouveia

  I am using a retained mode renderer similar to the display lists in Flash. In other words, I have a scene graph data structure called the Stage to which I add the graphical primitives I would like to see rendered, such as images, animations, text. For simplicity I'll refer to them as Sprites. Now I'm implementing an architecture which is becoming very similar to MVC, but I feel that that instead of having to create View classes, that the sprites already behave pretty much like Views (except for not being explicitly connected to the Model). And since the Model is only changed through the Controller, I could simply update the view together with the Model in the controller, as in the example below: Example 1 class Controller { Model model; Sprite view; void TeleportTo(Vector2 position) { model.Position = view.Position = position; } } The alternative, I think, would be to create View classes that wrap the sprites, make the model observable, and make the view react to changes on the model. This seems like a lot of extra work and boilerplate code, and I'm not seeing the benefits if I'm just going to have one view per controller. Example 2 class Controller { Model model; View view; void TeleportTo(Vector2 position) { model.Position = position; } } class View { Model model; Sprite sprite; View() { model.PropertyChanged += UpdateView; } void UpdateView() { sprite.Position = model.Position; } } So, how is MVC or more specifically, the View, usually implemented when using a retained-mode renderer? And is there any reason why I shouldn't stick with example 1?

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• How to keep balance / Unlock items / achievement rules

  - by Mark Knol

  I'm working on an engine for a game, too learn javascript and just because its fun. I'm a flashdeveloper, I know how to build websites. Now making games is a different challenge, javascript is a challenge, but I'd love to learn how to structure code and what patterns are common. I dont mind if the game ever finish, I'm mostly interested in the programming part of it. I dont have a particular endresult in mind, so I'll see where it takes me. I currently have a system where you can buy items. The items cost a specified amount of gold, silver, diamonds etc. When you have selected and bought the item, it takes time before getting rewarded. When time is over, you are getting rewarded with other properties (gold, energy, diamonds). For example, you can buy an apple for 50gold, It takes a minute, you get rewarded with 75energy. Or if you take a run, it cost 50energy, it takes 5minutes, reward is 25gold and 25silver. These definitions is what i call actions. Currently I already have a system where this already works and I can define as much actions with as much properties as I want. The definitions I have kinda looks like this: {id:101, category:544, onInit:{gold:-75}, onComplete:{energy:75}, time:2000, name:"Apple", locked: false} {id:102, category:544, onInit:{gold:-135}, onComplete:{energy:145}, time:2000, name:"Banana", locked: false} {id:106, category:302, onInit:{energy:-50, power: -25}, onComplete:{gold:100, diamonds:2}, time:10000, name:"Run", locked: false} {id:107, category:302, onInit:{energy:-70, silver: -55}, onComplete:{gold:100}, time:10000, name:"Dance", locked: false} {id:108, category:302, onInit:{energy:-230, power: -355}, onComplete:{gold:70, silver:70}, time:10000, name:"Fitness", locked: false} Now, I would love to add a system where I can lock/unlock the actions using achievement rules. Lets say, if you buy 10 apples, you unlock a new action, like bananas which cost more, and reward more. In the future I maybe want to restrict achievements and actions to levels. I am kinda stuck how to structure this. I have 2 questions: Which patterns are used to define achievements? How/where are they defined? Should it be part of the action, or should it be a separate controller? Is it a good idea to register all completed actions to it? I think I want multiple types of achievement rules, Id love to hear some ideas how to develop it. How do you create/find a good balance, so the user does not get stuck or can cheat by repeat a pattern of actions to get too much rewards. I know there is not a simple answer and i'm lacking of a good game-concept, but I wonder if anyone created such a game and how you dealed and played with it.

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• Write own messaging system vs. utilize existing ones

  - by A.Rashad

  We are trying to have our own startup, with a middleware application to glue small applications with enterprise legacy systems. for such middle-ware to function properly, we will need some sort of messaging system to make different components talk to each other in a reliable way. the alternatives are: use an existing messaging system, such as 0MQ, jBOSS, WebSphere MQ, etc. build our own messaging system the way we see the problem I am more biased towards the later option for the following reasons: to have more control over our final product to avoid any licensing problems later on to learn about messaging while writing the code to invent something new, that might cost us lots of $$$ if reused an existing system What would you do if in my shoes?

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