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• How Visual WebGui helps ASP.NET Cloud-based apps

  - by Visual WebGui

  Everyone is talking about Cloud computing and moving to the cloud (public or private), but very few have actually done it so far. The reason is that the process of migrating existing applications to the cloud is a lot more complicated than one might think which is exactly where the Visual WebGui technology comes in for a rescue. In the past year the Visual WebGui R&D Team have been intensively working on a tool-based solution that gives Microsoft application developers and enterprises a simpler...(read more)

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• Developing a Cost Model for Cloud Applications

  - by BuckWoody

  Note - please pay attention to the date of this post. As much as I attempt to make the information below accurate, the nature of distributed computing means that components, units and pricing will change over time. The definitive costs for Microsoft Windows Azure and SQL Azure are located here, and are more accurate than anything you will see in this post: http://www.microsoft.com/windowsazure/offers/  When writing software that is run on a Platform-as-a-Service (PaaS) offering like Windows Azure / SQL Azure, one of the questions you must answer is how much the system will cost. I will not discuss the comparisons between on-premise costs (which are nigh impossible to calculate accurately) versus cloud costs, but instead focus on creating a general model for estimating costs for a given application. You should be aware that there are (at this writing) two billing mechanisms for Windows and SQL Azure: “Pay-as-you-go” or consumption, and “Subscription” or commitment. Conceptually, you can consider the former a pay-as-you-go cell phone plan, where you pay by the unit used (at a slightly higher rate) and the latter as a standard cell phone plan where you commit to a contract and thus pay lower rates. In this post I’ll stick with the pay-as-you-go mechanism for simplicity, which should be the maximum cost you would pay. From there you may be able to get a lower cost if you use the other mechanism. In any case, the model you create should hold. Developing a good cost model is essential. As a developer or architect, you’ll most certainly be asked how much something will cost, and you need to have a reliable way to estimate that. Businesses and Organizations have been used to paying for servers, software licenses, and other infrastructure as an up-front cost, and power, people to the systems and so on as an ongoing (and sometimes not factored) cost. When presented with a new paradigm like distributed computing, they may not understand the true cost/value proposition, and that’s where the architect and developer can guide the conversation to make a choice based on features of the application versus the true costs. The two big buckets of use-types for these applications are customer-based and steady-state. In the customer-based use type, each successful use of the program results in a sale or income for your organization. Perhaps you’ve written an application that provides the spot-price of foo, and your customer pays for the use of that application. In that case, once you’ve estimated your cost for a successful traversal of the application, you can build that into the price you charge the user. It’s a standard restaurant model, where the price of the meal is determined by the cost of making it, plus any profit you can make. In the second use-type, the application will be used by a more-or-less constant number of processes or users and no direct revenue is attached to the system. A typical example is a customer-tracking system used by the employees within your company. In this case, the cost model is often created “in reverse” - meaning that you pilot the application, monitor the use (and costs) and that cost is held steady. This is where the comparison with an on-premise system becomes necessary, even though it is more difficult to estimate those on-premise true costs. For instance, do you know exactly how much cost the air conditioning is because you have a team of system administrators? This may sound trivial, but that, along with the insurance for the building, the wiring, and every other part of the system is in fact a cost to the business. There are three primary methods that I’ve been successful with in estimating the cost. None are perfect, all are demand-driven. The general process is to lay out a matrix of: components units cost per unit and then multiply that times the usage of the system, based on which components you use in the program. That sounds a bit simplistic, but using those metrics in a calculation becomes more detailed. In all of the methods that follow, you need to know your application. The components for a PaaS include computing instances, storage, transactions, bandwidth and in the case of SQL Azure, database size. In most cases, architects start with the first model and progress through the other methods to gain accuracy. Simple Estimation The simplest way to calculate costs is to architect the application (even UML or on-paper, no coding involved) and then estimate which of the components you’ll use, and how much of each will be used. Microsoft provides two tools to do this - one is a simple slider-application located here: http://www.microsoft.com/windowsazure/pricing-calculator/  The other is a tool you download to create an “Return on Investment” (ROI) spreadsheet, which has the advantage of leading you through various questions to estimate what you plan to use, located here: https://roianalyst.alinean.com/msft/AutoLogin.do?d=176318219048082115  You can also just create a spreadsheet yourself with a structure like this: Program Element Azure Component Unit of Measure Cost Per Unit Estimated Use of Component Total Cost Per Component Cumulative Cost               Of course, the consideration with this model is that it is difficult to predict a system that is not running or hasn’t even been developed. Which brings us to the next model type. Measure and Project A more accurate model is to actually write the code for the application, using the Software Development Kit (SDK) which can run entirely disconnected from Azure. The code should be instrumented to estimate the use of the application components, logging to a local file on the development system. A series of unit and integration tests should be run, which will create load on the test system. You can use standard development concepts to track this usage, and even use Windows Performance Monitor counters. The best place to start with this method is to use the Windows Azure Diagnostics subsystem in your code, which you can read more about here: http://blogs.msdn.com/b/sumitm/archive/2009/11/18/introducing-windows-azure-diagnostics.aspx This set of API’s greatly simplifies tracking the application, and in fact you can use this information for more than just a cost model. After you have the tracking logs, you can plug the numbers into ay of the tools above, which should give a representative cost or in some cases a unit cost. The consideration with this model is that the SDK fabric is not a one-to-one comparison with performance on the actual Windows Azure fabric. Those differences are usually smaller, but they do need to be considered. Also, you may not be able to accurately predict the load on the system, which might lead to an architectural change, which changes the model. This leads us to the next, most accurate method for a cost model. Sample and Estimate Using standard statistical and other predictive math, once the application is deployed you will get a bill each month from Microsoft for your Azure usage. The bill is quite detailed, and you can export the data from it to do analysis, and using methods like regression and so on project out into the future what the costs will be. I normally advise that the architect also extrapolate a unit cost from those metrics as well. This is the information that should be reported back to the executives that pay the bills: the past cost, future projected costs, and unit cost “per click” or “per transaction”, as your case warrants. The challenge here is in the model itself - statistical methods are not foolproof, and the larger the sample (in this case I recommend the entire population, not a smaller sample) is key. References and Tools Articles: http://blogs.msdn.com/b/patrick_butler_monterde/archive/2010/02/10/windows-azure-billing-overview.aspx http://technet.microsoft.com/en-us/magazine/gg213848.aspx http://blog.codingoutloud.com/2011/06/05/azure-faq-how-much-will-it-cost-me-to-run-my-application-on-windows-azure/ http://blogs.msdn.com/b/johnalioto/archive/2010/08/25/10054193.aspx http://geekswithblogs.net/iupdateable/archive/2010/02/08/qampa-how-can-i-calculate-the-tco-and-roi-when.aspx   Other Tools: http://cloud-assessment.com/ http://communities.quest.com/community/cloud_tools

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• Windows Cloud Services Aren’t Exclusive to Microsoft

  - by Ken Cox [MVP]

  The Windows Azure brand has captured mindshare for the buzzword-du-jour, ‘cloud computing’. However, Microsoft certainly isn’t the only option for cranking up virtual machines to meet unexpected or peak demands. For example, I see that OrcsWeb has released its Windows Cloud Servers product , starting at $99.99 a month*.  Competition is a good thing - and make sure you do some cost comparisons when researching cloud resources. Some of us were unpleasantly surprised by Azure’s pricing structure...(read more)

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• Come up with a real-world problem in which only the best solution will do (a problem from Introduction to algorithms) [closed]

  - by Mike

  EDITED (I realized that the question certainly needs a context) The problem 1.1-5 in the book of Thomas Cormen et al Introduction to algorithms is: "Come up with a real-world problem in which only the best solution will do. Then come up with one in which a solution that is “approximately” the best is good enough." I'm interested in its first statement. And (from my understanding) it is asked to name a real-world problem where only the exact solution will work as opposed to a real-world problem where good-enough solution will be ok. So what is the difference between the exact and good enough solution. Consider some physics problem for example the simulation of the fulid flow in the permeable medium. To make this simulation happen some simplyfing assumptions have to be made when deriving a mathematical model. Otherwise the model becomes at least complex and unsolvable. Virtually any particle in the universe has its influence on the fluid flow. But not all particles are equal. Those that form the permeable medium are much more influental than the ones located light years away. Then when the mathematical model needs to be solved an exact solution can rarely be found unless the mathematical model is simple enough (wich probably means the model isn't close to reality). We take an approximate numerical method and after hours of coding and days of verification come up with the program or algorithm which is a solution. And if the model and an algorithm give results close to a real problem by some degree that is good enough soultion. Its worth noting the difference between exact solution algorithm and exact computation result. When considering real-world problems and real-world computation machines I believe all physical problems solutions where any calculations are taken can not be exact because universal physical constants are represented approximately in the computer. Any numbers are represented with the limited precision, at least limited by amount of memory available to computing machine. I can imagine plenty of problems where good-enough, good to some degree solution will work, like train scheduling, automated trading, satellite orbit calculation, health care expert systems. In that cases exact solutions can't be derived due to constraints on computation time, limitations in computer memory or due to the nature of problems. I googled this question and like what this guy suggests: there're kinds of mathematical problems that need exact solutions (little note here: because the question is taken from the book "Introduction to algorithms" the term "solution" means an algorithm or a program, which in this case gives exact answer on each input). But that's probably more of theoretical interest. So I would like to narrow down the question to: What are the real-world practical problems where only the best (exact) solution algorithm or program will do (but not the good-enough solution)? There are problems like breaking of cryptographic ciphers where only exact solution matters in practice and again in practice the process of deciphering without knowing a secret should take reasonable amount of time. Returning to the original question this is the problem where good-enough (fast-enough) solution will do there's no practical need in instant crack though it's desired. So the quality of "best" can be understood in any sense: exact, fastest, requiring least memory, having minimal possible network traffic etc. And still I want this question to be theoretical if possible. In a sense that there may be example of computer X that has limited resource R of amount Y where the best solution to problem P is the one that takes not more than available Y for inputs of size N*Y. But that's the problem of finding solution for P on computer X which is... well, good enough. My final thought that we live in a world where it is required from programming solutions to practical purposes to be good enough. In rare cases really very very good but still not the best ones. Isn't it? :) If it's not can you provide an example? Or can you name any such unsolved problem of practical interest?

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• What is Quantum Computing? Microsoft’s video explains it in simple language

  - by Gopinath

  Quantum Computing is the next promising big thing to happen in computer science and its going to revolutionize the way we solve problem using computers. To explain the concepts of Quantum Computing to common man, Microsoft released a nice video which gives brief introduction to the concepts, explains the benefits and the work being carried out by Microsoft to make this technology research a reality. Check out this embedded video and visit Microsoft’s website for more details on Quantum Computing.

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• Windows Azure Use Case: Agility

  - by BuckWoody

  This is one in a series of posts on when and where to use a distributed architecture design in your organization's computing needs. You can find the main post here: http://blogs.msdn.com/b/buckwoody/archive/2011/01/18/windows-azure-and-sql-azure-use-cases.aspx  Description: Agility in this context is defined as the ability to quickly develop and deploy an application. In theory, the speed at which your organization can develop and deploy an application on available hardware is identical to what you could deploy in a distributed environment. But in practice, this is not always the case. Having an option to use a distributed environment can be much faster for the deployment and even the development process. Implementation: When an organization designs code, they are essentially becoming a Software-as-a-Service (SaaS) provider to their own organization. To do that, the IT operations team becomes the Infrastructure-as-a-Service (IaaS) to the development teams. From there, the software is developed and deployed using an Application Lifecycle Management (ALM) process. A simplified view of an ALM process is as follows: Requirements Analysis Design and Development Implementation Testing Deployment to Production Maintenance In an on-premise environment, this often equates to the following process map: Requirements Business requirements formed by Business Analysts, Developers and Data Professionals. Analysis Feasibility studies, including physical plant, security, manpower and other resources. Request is placed on the work task list if approved. Design and Development Code written according to organization’s chosen methodology, either on-premise or to multiple development teams on and off premise. Implementation Code checked into main branch. Code forked as needed. Testing Code deployed to on-premise Testing servers. If no server capacity available, more resources procured through standard budgeting and ordering processes. Manual and automated functional, load, security, etc. performed. Deployment to Production Server team involved to select platform and environments with available capacity. If no server capacity available, standard budgeting and procurement process followed. If no server capacity available, systems built, configured and put under standard organizational IT control. Systems configured for proper operating systems, patches, security and virus scans. System maintenance, HA/DR, backups and recovery plans configured and put into place. Maintenance Code changes evaluated and altered according to need. In a distributed computing environment like Windows Azure, the process maps a bit differently: Requirements Business requirements formed by Business Analysts, Developers and Data Professionals. Analysis Feasibility studies, including budget, security, manpower and other resources. Request is placed on the work task list if approved. Design and Development Code written according to organization’s chosen methodology, either on-premise or to multiple development teams on and off premise. Implementation Code checked into main branch. Code forked as needed. Testing Code deployed to Azure. Manual and automated functional, load, security, etc. performed. Deployment to Production Code deployed to Azure. Point in time backup and recovery plans configured and put into place.(HA/DR and automated backups already present in Azure fabric) Maintenance Code changes evaluated and altered according to need. This means that several steps can be removed or expedited. It also means that the business function requesting the application can be held directly responsible for the funding of that request, speeding the process further since the IT budgeting process may not be involved in the Azure scenario. An additional benefit is the “Azure Marketplace”, In effect this becomes an app store for Enterprises to select pre-defined code and data applications to mesh or bolt-in to their current code, possibly saving development time. Resources: Whitepaper download- What is ALM?  http://go.microsoft.com/?linkid=9743693  Whitepaper download - ALM and Business Strategy: http://go.microsoft.com/?linkid=9743690  LiveMeeting Recording on ALM and Windows Azure (registration required, but free): http://www.microsoft.com/uk/msdn/visualstudio/contact-us.aspx?sbj=Developing with Windows Azure (ALM perspective) - 10:00-11:00 - 19th Jan 2011

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• Storing Projects on Google Drive (Cloud)

  - by JamesKraw

  I've started using Google Drive for my cloud needs and backing up pretty much everything. I've got the app installed so it auto-sync's all my content in most things. My question is this, I am currently coding for iOS (although this applies to any coding project) and am split on storing my project files on Google Drive while using sync. My theory is that if I did use it, I'd never have to worry about system crashes or lost code before backups, but if I do use it it will be sync'ing a-lot and I thought there might be problems with it detecting changes and trying to sync for example half way through compiling. Bandwidth isn't an issue as I have fast connection and unlimited monthly allowance. Has anyone ever used this, or similar cloud-based sync'ing (dropbox etc) for this and knows whether it works or not or whether there are any potential problems etc.

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• Has RFC2324 been implemented?

  - by anthony-arnold

  I know RFC2324 was an April Fools joke. However, it seems pretty well thought out, and after reading it I figured it wouldn't be out of the question to design an automated coffee machine that used this extension to HTTP. We programmers love to reference this RFC when arguing web standards ("418 I'm a Teapot lolz!") but the joke's kind of on us. Ubiquitous computing research assumes that network-connected coffee machines are probably going to be quite common in the future, along with Internet-connected fruit and just about everything else. Has anyone actually implemented a coffee machine that is controlled via HTCPCP? Not necessarily commercial, but hacked together in a garage, maybe? I'm not talking about just a web server that responds to HTCPCP requests; I mean a real coffee machine that actually makes coffee. I haven't seen an example of that.

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• Microsoft launches two new Data Centres for Azure in US to meet growing demand

  - by Gopinath

  In order to meet the growing demand for Windows Azure in US, Microsoft has launched two new data centres in US – East US and West US. With the addition of these two data centres the number of Azure data centres across the globe has grown to 8 and 4 among them are located in US. The two new data centres are providing Computer and Storage resources and few enthusiastic customers already deployed their applications. The other services like SQL Azure and AppFabric will be offered by these data centres in the coming months. The addition of new data centres is a good sign to Microsoft as the customer demand for their Cloud offering is growing. Amazon Web Services is the pioneer in Cloud Computing and they offer wider range of Cloud Services compared to Microsoft. Source: Windows Azure Blog

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• Using Resources the Right Way

  - by BuckWoody

  It’s an interesting time in computing technology. At one point there was a dearth of information available for solving a given problem, or educating ourselves on broader topics so that we can solve problems in the future. With dozens, perhaps hundreds or thousands of web sites and content available (for free, in many cases) from vendors, peers, even colleges and universities, it seems like there is actually too much information. Who has the time to absorb all this information and training? Even if you had the inclination, where to start? In fact, it seems so overwhelming that I often hear people saying that they can’t find the training they need, or that vendor X or Y “doesn’t help their users”. On questioning these folks, however, I often find that they – and sometimes I - haven’t put in the effort to learn what resources we have. That’s where blogs, like this one, can help. If you follow a blog, either by checking it often or perhaps subscribing to the Really Simple Syndication (RSS) feed, you’ll be able to spread out the search or create a mental filter for the information you need. But it’s not enough just read a blog or a web page. The creators need real feedback – what doesn’t work, and what does. Yes, you’re allowed to tell a vendor or writer “This helped me because…” so that you reinforce the positives. To be sure, bring up what doesn’t work as well –  that’s fine. But be specific, and be constructive. You’d be surprised at how much it matters. I know for a fact at Microsoft we listen – there is a real live person that reads your comments. I’m sure this is true of other vendors, and I also know that most blog authors – yours truly most especially – wants to know what you think.   In this blog entry I’d to call your attention to three resources you have at your disposal, and how you can use them to help. I’ll try to bring up things like this from time to time that I find useful, and cover in them in more depth like this. Think of this as a synopsis of a longer set of resources that you can use to filter whether you want to research further, bookmark, or forward on to a circle of friends where you think it might help them.   Data Driven Design Concepts http://msdn.microsoft.com/en-us/library/windowsazure/jj156154 I’ll start with a great site that walks you through the process of designing a solution from a data-first perspective. As you know, I believe all computing is merely re-arranging data. If you follow that logic as well, you’ll realize that whenever you create a solution, you should start at the data-end of the application. This resource helps you do that. Even if you don’t use the specific technologies the instructions use, the concepts hold for almost any other technology that deals with data. This should be a definite bookmark for a developer, DBA, or Data Architect. When I mentioned my admiration for this resource here at Microsoft, the team that created it contacted me and asked if I’d share an e-mail address to my readers so that you can comment on it. You’re guaranteed to be heard – you can suggest changes, talk about how useful – or not – it is, and so on. Here’s that address:  [email protected]   End-to-End Example of a complete Hybrid Application – with Live Demo https://azurestocktrader.cloudapp.net/Default.aspx I learn by example. I also like having ready-made, live, functional demos that show the completed solution at work. If you’ve ever wanted to learn how a complex, complete, hybrid application that bridges on-premises systems with cloud-based databases, code, functions and more, this is it. It’s a stock-trading simulator, and you can get everything from the design to the code itself, or you can just play with the application. It’s running on Windows Azure, the actual production servers we use for everything else. Using a Cloud-Based Service https://azureconfigweb.cloudapp.net/Default.aspx Along with that stock-trading application, you have a full demonstration and usable code sample of a web-based service available. If you’re a developer, this is a style of code you need to understand for everything from iPhone development to a full Service-Oriented Architecture (SOA) environment. So check out these resources. I’ll post more from time to time as I run across them. Hopefully they’ll be as useful to you as they are to me. Oh, and if you have a comment on any of the resources, let them know. And if you have any comments about these or any of my entries, feel free to post away. To quote a famous TV Show: “Hello Seattle – I’m listening…”

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• Ray-box Intersection Theory

  - by Myx

  Hello: I wish to determine the intersection point between a ray and a box. The box is defined by its min 3D coordinate and max 3D coordinate and the ray is defined by its origin and the direction to which it points. Currently, I am forming a plane for each face of the box and I'm intersecting the ray with the plane. If the ray intersects the plane, then I check whether or not the intersection point is actually on the surface of the box. If so, I check whether it is the closest intersection for this ray and I return the closest intersection. The way I check whether the plane-intersection point is on the box surface itself is through a function bool PointOnBoxFace(R3Point point, R3Point corner1, R3Point corner2) { double min_x = min(corner1.X(), corner2.X()); double max_x = max(corner1.X(), corner2.X()); double min_y = min(corner1.Y(), corner2.Y()); double max_y = max(corner1.Y(), corner2.Y()); double min_z = min(corner1.Z(), corner2.Z()); double max_z = max(corner1.Z(), corner2.Z()); if(point.X() >= min_x && point.X() <= max_x && point.Y() >= min_y && point.Y() <= max_y && point.Z() >= min_z && point.Z() <= max_z) return true; return false; } where corner1 is one corner of the rectangle for that box face and corner2 is the opposite corner. My implementation works most of the time but sometimes it gives me the wrong intersection. I was wondering if the way I'm checking whether the intersection point is on the box is correct or if I should use some other algorithm. Thanks.

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• Database theory - relationship between two tables

  - by iansinke

  I have a database with two tables - let's call them Foo and Bar. Each foo may be related to any number of bars, and each bar may be related to any number of foos. I want to be able to retrieve, with one query, the foos that are associated with a certain bar, and the bars that are associated with a certain foo. My question is, what is the best way of recording these relationships? Should I have a separate table with records of each relationship (e.g. two columns, foo and bar)? Should the foo table have a column for a list of bars, and vice versa? Is there another option that I'm overlooking? I'm using SQL Server, if that makes a difference.

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• Traceroute Theory

  - by Hamza Yerlikaya

  I am toying with trace route, my application send a ICMP echo request with a ttl of 0 every time i receive a time exceeded message i increment the ttl by one and resent the package, but what happens is I have 2 routers on my network i can trace the route through these router but third hop always ends up being one of the open dns servers same ip every time no matter where i traceroute to. AFAIK this is the correct traceroute implementation, can anyone tell me what i am doing wrong?

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• Discrete mathematics problem - Probability theory and counting

  - by Mohammad

  Hello All, I'm taking a discrete mathematics course, and I encountered a question and I need your help. I don't know if this is the right place for that though :) It says: Each user on a computer system has a password, which is six to eight characters long, where each character is an uppercase letter or a digit. Each password must contain at least one digit. How many possible passwords are there? The book solves this by adding the probabilities of having six,seven and eight characters long password. However, when he solves for probability of six characters he does this P6 = 36^6 - 26^6 and does P7 = 36^7 - 26^7 and P8 = 36^8 - 26^8 and then add them all I understand the solution, but my question is why doesn't calculating, P6 = 10*36^5 and the same for P7 and P8, work? 10 for the digit and 36 for the alphanumeric? Also, if anyone could give me another solution, other than the one in the book. Thank you very much :)

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• Significant new inventions in computing since 1980

  - by Alan Kay

  This question arose from comments about different kinds of progress in computing over the last 50 years or so. I was asked by some of the other participants to raise it as a question to the whole forum. Basic idea here is not to bash the current state of things but to try to understand something about the progress of coming up with fundamental new ideas and principles. I claim that we need really new ideas in most areas of computing, and I would like to know of any important and powerful ones that have been done recently. If we can't really find them, then we should ask "Why?" and "What should we be doing?"

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• Pros and cons of cloud computing?

  - by Vimvq1987

  After 3 months of research, my thesis is nearly complete. Now I'm writing the report. Interesting parts are finished, now the boring and hard-to-write parts. I need to write about pros and cons of cloud computing. What it gives us and what it take us. I've searched much but there's only list, no explains. So I need your helps, to list and explains all of pros and cons of cloud computing. Thank you so much for this.

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• Theory of Game Interface Design

  - by anon

  Anyone know of a good book on Game Interface Design (not game play mechanics; the actual UI). I'm particular interested in theories of cognition, and how game interfaces are designed to allow the enduser efficient communication with the game (whether it in FPS, RTS, or so on). In a modern game, the amount of information conveyed to the user, the amount of choices the user can make; and the support for the user to make said decisions is simply astounding (think UIs for Starcraft II / WoW). Any insights into this would be greatly appreciated.

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• How to put theory into practise

  - by Dave greg

  I like to read alot of IT books e.g programming / functional. But the problem is that after reading I cannot find reasons to put it into practise and I soon forget what I read. Any advise?

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• Permutations distinct under given symmetry (Mathematica 8 group theory)

  - by Yaroslav Bulatov

  Given a list of integers like {2,1,1,0} I'd like to list all permutations of that list that are not equivalent under given group. For instance, using symmetry of the square, the result would be {{2, 1, 1, 0}, {2, 1, 0, 1}}. Approach below (Mathematica 8) generates all permutations, then weeds out the equivalent ones. I can't use it because I can't afford to generate all permutations, is there a more efficient way? Update: actually, the bottleneck is in DeleteCases. The following list {2, 2, 2, 2, 2, 2, 2, 1, 1, 1, 1, 1, 1, 0, 0, 0} has about a million permutations and takes 0.1 seconds to compute. Apparently there are supposed to be 1292 orderings after removing symmetries, but my approach doesn't finish in 10 minutes removeEquivalent[{}] := {}; removeEquivalent[list_] := ( Sow[First[list]]; equivalents = Permute[First[list], #] & /@ GroupElements[group]; DeleteCases[list, Alternatives @@ equivalents] ); nonequivalentPermutations[list_] := ( reaped = Reap@FixedPoint[removeEquivalent, Permutations@list]; reaped[[2, 1]] ); group = DihedralGroup[4]; nonequivalentPermutations[{2, 1, 1, 0}]

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• Goldbach theory in C

  - by nofe

  I want to write some code which takes any positive, even number (greater than 2) and gives me the smallest pair of primes that sum up to this number. I need this program to handle any integer up to 9 digits long. My aim is to make something that looks like this: Please enter a positive even integer ( greater than 2 ) : 10 The first primes adding : 3+7=10. Please enter a positive even integer ( greater than 2 ) : 160 The first primes adding : 3+157=160. Please enter a positive even integer ( greater than 2 ) : 18456 The first primes adding : 5+18451=18456. I don't want to use any library besides stdio.h. I don't want to use arrays, strings, or anything besides for the most basic toolbox: scanf, printf, for, while, do-while, if, else if, break, continue, and the basic operators (<,, ==, =+, !=, %, *, /, etc...). Please no other functions especially is_prime. I know how to limit the input to my needs so that it loops until given a valid entry. So now I'm trying to figure out the algorithm. I thought of starting a while loop like something like this: #include <stdio.h> long first, second, sum, goldbach, min; long a,b,i,k; //indices int main (){ while (1){ printf("Please enter a positive integer :\n"); scanf("%ld",&goldbach); if ((goldbach>2)&&((goldbach%2)==0)) break; else printf("Wrong input, "); } while (sum!=goldbach){ for (a=3;a<goldbach;a=(a+2)) for (i=2;(goldbach-a)%i;i++) first = a; for (b=5;b<goldbach;b=(b+2)) for (k=2;(goldbach-b)%k;k++) sum = first + second; } }

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• SQL Query Theory Question...

  - by Keng

  I have a large historical transaction table (15-20 million rows MANY columns) and a table with one row one column. The table with one row contains a date (last processing date) which will be used to pull the data in the trasaction table ('process_date'). Question: Should I inner join the 'process_date' table to the transaction table or the transaction table to the 'process_date' table?

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• C: theory on how to extract files from an archived file

  - by donok

  In C I have created a program which can archive multiple files into an archive file via the command line. e.g. $echo 'file1/2' > file1/2.txt $./archive file1.txt file2.txt arhivedfile $cat archivedfile file1 file2 How do I create a process so that in my archivedfile I have: header file1 end header file2 end They are all stored in the archive file one after another after another. I know that perhaps a header file is needed(containing filename, size of filename, start and end of file) for extracting these files back out into their original form, but how would I go about doing this. I am stuck on where and how to start. Please could someone help me on some logic as to how to approach extracting files back out of an archived file.

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• Very basic database theory.

  - by John R

  I have a set of tables to show the relationship between organziations and supporters below. Although I have done some basic mySQL querries, I know very little about database 'design'. I plan to querry the database for: -a list of contributors to a specific organization... or, -a list of organizations that a specific suporter supports. The database tables for organiations and contributors may have other columns in the future and recieve a lesser amount of querries based on that information. A | X A | Y A | Z B | X B | Y C | X C | Z How should the tables be set up? I assume that there should be a third table, but there is still redundent information in the third table. Is there a better way of setting up the tables? +----+-------+ +-------------+----------+ +----+-------+ | id | org | | org | contr | | id | contr.| +----+-------+ +-------------+----------+ +----+-------+ | 1 | A | | 1 | 1 | | 1 | X | | 2 | B | | 1 | 2 | | 2 | Y | | 3 | C | | 1 | 3 | | 3 | Z | +----+-------+ | 2 | 1 | +----+-------+ | 2 | 2 | | 3 | 1 | | 3 | 3 | +-------------+----------+

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• Lançamento do Oracle Enterprise Manager 11g - (27/Mai/10)

  - by Claudia Costa

  Não perca este evento exclusivo para executivos, responsáveis de TI e Parceiros Oracle, e explore em que medida a versão mais recente do Oracle Enterprise Manager permite que a gestão das TI seja orientada para o negócio. Registe-se hoje! Descubra as novas capacidades do Oracle Enterprise Manager 11g, que incluem: ·         Gestão integrada, desda a aplicação até ao Cloud Computing, visando a maximização do retorno do investimento em TI ·         Gestão de aplicações orientadas para o negócio, que permte ao departamento de TI identificar e corrigir os problemas antes de estes terem impacto no negócio ·         Gestão e suporte intregrados dos sistemas, fornecendo notificações e correcções proactivas, associadas à partilha de conhecimento entre pares, para aumentar a satisfação dos clientes Junte-se a nós e fique a saber como somente o Oracle Enterprise Manager 11g pode ajudar as TI a melhorarem proactivamente o valor empresarial em diversas tecnologias, incluindo sistemas Sun; sistema operativo Oracle Solaris; Oracle Database; Oracle Fusion Middleware; Oracle E Business Suite; soluções Siebel, PeopleSoft e JD Edwards da Oracle; tecnologias de virtualização e ambientes de nuvem privada. Irá decorrer uma sessão exclusiva para parceiros da Oracle onde falará de temas como a especialização e exploração de oportunidades de negócio conjunto nas áreas de Gestão de aplicações e sitemas. Agenda - Sana Lisboa Park Hotel Avenida Fontes Pereira de Melo, 8 Lisboa Quinta-Feira, 27 de Maio de 2010 Horario: 9:00- 15:30h 9:00    Registo e Café 9:30    Introdução 9:40    Keynote: Business-driven IT Mnagement with Oracle Enterprise Manager 11g 10:25  Experiências de Cliente 11:00  Pausa 11:15  Integrated Application-to-disk Mangement 11:45  Business-driven Application Management 12:15  Integrated Cloud Management 12:45  Integrated Systems Management and Support Experience 13:15  Almoço 14:30  Sessão para Parceiros - Especialização e Oportunidades de negócio com Oracle      Enterprise Manager   Registe-se hoje mesmo para reservar o seu lugar neste evento exclusivo.      

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• Building a Redundant / Distrubuted Application

  - by MattW

  This is more of a "point me in the right direction" question. I (and my team of 3) have built a hosted web app that queues and routes customer chat requests to available customer service agents (It does other things as well, but this is enough background to illustrate the issue). The basic dev architecture today is: a single page ajax web UI (ASP.NET MVC) with floating chat windows (think Gmail) a backend Windows service to queue and route the chat requests this service also logs the chats, calculates service levels, etc a Comet server product that routes data between the web frontend and the backend Windows service this also helps us detect which Agents are still connected (online) And our hardware architecture today is: 2 servers to host the web UI portion of the application a load balancer to route requests to the 2 different web app servers a third server to host the SQL Server DB and the backend Windows service responsible for queuing / delivering chats So as it stands today, one of the web app servers could go down and we would be ok. However, if something would happen to the SQL Server / Windows Service server we would be boned. My question - how can I make this backend Windows service logic be able to be spread across multiple machines (distributed)? The Windows service is written to accept requests from the Comet server, check for available Agents, and route the chat to those agents. How can I make this more distributed? How can I make it so that I can distribute the work of the backend Windows service can be spread across multiple machines for redundancy and uptime purposes? Will I need to re-write it with distributed computing in mind? I should also note that I am hosting all of this on Rackspace Cloud instances - so maybe it is something I should be less concerned about? Thanks in advance for any help!

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