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  • How can I test a parser for a bespoke XML schema?

    - by Greg B
    I'm parsing a bespoke XML format into an object graph using .NET 4.0. My parser is using the System.XML namespace internally, I'm then interrogating the relevant properties of XmlNodes to create my object graph. I've got a first cut of the parser working on a basic input file and I want to put some unit tests around this before I progress on to more complex input files. Is there a pattern for how to test a parser such as this? When I started looking at this, my first move was to new up and XmlDocument, XmlNamespaceManager and create an XmlElement. But it occurs to me that this is quite lengthy and prone to human error. My parser is quite recursive as you can imagine and this might lead to testing the full system rather than the individual units (methods) of the system. So a second question might be What refactoring might make a recursive parser more testable?

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  • Where to download replacement "Explorerframe.DLL" Files for x64 Windows 7 Pro?

    - by Ben Franchuk
    After posting this question, I did some research to reveal what the problem likely was, and found what I need to fix. Following this is the original post, then my updated question. A few months ago I ended up requiring to change my computer's SID to fix a problem it had been having- Instead of fixing the problem, though, it screwed up my at-the-time current install of windows, to the point of me needing to do a fresh install. As I am in possession of an OEM copy of Windows 7 Pro 64 Bit, I successfully reinstalled over the dead copy with that (all the files that were on the computer previous to this windows install were put in a Windows.old folder). Everything installed and worked absolutely fine, except for one thing. The problem I am experiencing is that, in some Windows Explorer windows, the explorer pane doesn't show. Instead, it simply shows a white area where the pane would show. This makes some software not usable, I recently realized; Software such as Cubase, which use just the explorer pane to select file save locations, cannot save at all as the pane itself is... not operational. Below is a screenshot of this problem as it occurs in cubase; ...and again as it shows in UTorrent in the save location selector window. The highlighted area is where the sidebar would NORMALLY be. Pardon my scribbling over some of the things in the window- I would personally rather the internet did not get a glimpse of my files. I have yet to find a common reason why the pane works in some applications when they pull explorer, and others not. I have yet to see it go away, and the software affected by it has been affected since I reinstalled my copy of windows. Initially, I was able to live with it as I can type out save locations in the file name bar to navigate, but with software like Cubase, I do not have this option. Reinstalling windows again is NOT an option. Here's the updated question. After posting this question originally, I did some research on the problem in question, and it turns out that this is extremely easily fixable via replacing the file "ExplorerFrame.DLL" which is located in the System32 and SystemWOW64 Folders, in the windows folder, on the C:\ drive. As I quite frequently customize my computer, this is a normal thing for me to do and I know exactly how to safely and properly replace this file. The only problem is that I cannot for the life of me find a download of this file that actually works with my computer. I tried a couple from some different sites but they all caused explorer to not restart (I was given an error when starting the application from Task Manager) and was forced to revert to the broken .DLL files. Since there are 2 separate "ExplorerFrame.DLL" files; one for 64 bit and the other for 32 bit, I am assuming that I will need to download 2 separate versions to replace the corrupted ones. Where can I acquire these files? I am currently running Windows 7 Professional x64 Bit.

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  • What does RESTful web applications mean? [closed]

    - by John Cooper
    Possible Duplicate: What is REST (in simple English) What does RESTful web applications mean? A web service is a function that can be accessed by other programs over the web (Http). To clarify a bit, when you create a website in PHP that outputs HTML its target is the browser and by extension the human being reading the page in the browser. A web service is not targeted at humans but rather at other programs. SOAP and REST are two ways of creating WebServices. Correct me if i am wrong? What are other ways i can create a WebService? What does it mean fully RESTful web Application?

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  • Process development lifecycle in Oracle BPM 11g

    - by mesriniv
       Oracle BPM 11g platform provides two modeling tools tailored to different audience. The BPM Process Composer component is a web-based, role-driven, collaborative platform for discovery, design and documentation of business processes aimed at business audience. It empowers the business user to participate in the definition, feedback and design of business processes. The other modeling tool is Oracle BPM Studio that runs in the JDeveloper IDE .  Irrespective of the tool used, same BPMN and related artifacts are authored - that is , this is not import/export but just multiple tools working with same assets. In addition to BPMN 2.0, both tools provides editors for process data, organizational roles, human tasks (including assignment and user interface), business rules. The Oracle BPM design-time repository (Oracle Metadata Services Repository) is the glue that facilitates shared work environment across multiple BPM Composer and Studio clients.This document explains how to create snapshots and versions of your BPM projects and captures best practices for shared process development lifecycle. http://java.net/projects/oraclebpmsuite11g/downloads/directory/Samples/bpm-122-processdevelopment-lifecycle

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  • What is the worst software bug in history? [closed]

    - by Amir Rezaei
    By having for example money and human suffering as the metric. What is the worst software bug in history? Note this is a specific question. Last month automaker Toyota announced a recall of 160,000 of its Prius hybrid vehicles following reports of vehicle warning lights illuminating for no reason, and cars' gasoline engines stalling unexpectedly. But unlike the large-scale auto recalls of years past, the root of the Prius issue wasn't a hardware problem -- it was a programming error in the smart car's embedded code. The Prius had a software bug.

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  • What are best practices for testing programs with stochastic behavior?

    - by John Doucette
    Doing R&D work, I often find myself writing programs that have some large degree of randomness in their behavior. For example, when I work in Genetic Programming, I often write programs that generate and execute arbitrary random source code. A problem with testing such code is that bugs are often intermittent and can be very hard to reproduce. This goes beyond just setting a random seed to the same value and starting execution over. For instance, code might read a message from the kernal ring buffer, and then make conditional jumps on the message contents. Naturally, the ring buffer's state will have changed when one later attempts to reproduce the issue. Even though this behavior is a feature it can trigger other code in unexpected ways, and thus often reveals bugs that unit tests (or human testers) don't find. Are there established best practices for testing systems of this sort? If so, some references would be very helpful. If not, any other suggestions are welcome!

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  • Evidence for automatic browsing - Log file analysis

    - by Nilani Algiriyage
    I'm analyzing web server logs both in Apache and IIS log formats. I want to find the evidence for automatic browsing, like web robots, spiders, bots, etc. I used python robot-detection 0.2.8 for detecting robots in my log files, but I know there may be other robots (automatic programs) which have traversed through the web site but robot-detection can not identify. So I want to ask: Are there any specific clues that can be found in log files that human users do not leave but automated software would? Do they follow a specific navigation pattern? I saw some requests for favicon.ico - does this implicate that it is a automatic browsing?. I found this article and this question with some valuable points.

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  • if ('constant' == $variable) vs. if ($variable == 'constant')

    - by Tom Auger
    Lately, I've been working a lot in PHP and specifically within the WordPress framework. I'm noticing a lot of code in the form of: if ( 1 == $options['postlink'] ) Where I would have expected to see: if ( $options['postlink'] == 1 ) Is this a convention found in certain languages / frameworks? Is there any reason the former approach is preferable to the latter (from a processing perspective, or a parsing perspective or even a human perspective?) Or is it merely a matter of taste? I have always thought it better when performing a test, that the variable item being tested against some constant is on the left. It seems to map better to the way we would ask the question in natural language: "if the cake is chocolate" rather than "if chocolate is the cake".

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  • 1 Zettabyte Is Equal to 1 Million Petabytes

    - by Gopinath
    Geeks recently coined a new English term, Zettabyte, to measure the rapidly growing digital information footprint. So what is a Zettabyte? A Zettabyte is equal to 1 million Petabytes or 1 trillion terabytes and 1 quadrillion gigabytes. Symbol To Represent Zettabyte According to wikipedia the symbol ZB is used to represent a Zettabyte. So we can write 10 ZB to represent 10 Zettabytes. Human’s Digital Output Will be 1.2 Zettabytes By End Of 2010 Are you wondering why do we need a term to measure digital data? Tech research firm IDC has recently published a report that estimates current digital footprint created by us so far at 8 million Petabytes – the equivalent of 8,000,000,000,000 GB. This foot print is expected to pass 1.2 Zettabytes by the end of 2010. cc image credit:flickr Join us on Facebook to read all our stories right inside your Facebook news feed.

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  • UIView with IrrlichtScene - iOS

    - by user1459024
    i have a UIViewController in a Storyboard and want to draw a IrrlichtScene in this View Controller. My Code: WWSViewController.h #import <UIKit/UIKit.h> @interface WWSViewController : UIViewController { IBOutlet UILabel *errorLabel; } @end WWSViewController.mm #import "WWSViewController.h" #include "../../ressources/irrlicht/include/irrlicht.h" using namespace irr; using namespace core; using namespace scene; using namespace video; using namespace io; using namespace gui; @interface WWSViewController () @end @implementation WWSViewController -(void)awakeFromNib { errorLabel = [[UILabel alloc] init]; errorLabel.text = @""; IrrlichtDevice *device = createDevice( video::EDT_OGLES1, dimension2d<u32>(640, 480), 16, false, false, false, 0); /* Set the caption of the window to some nice text. Note that there is an 'L' in front of the string. The Irrlicht Engine uses wide character strings when displaying text. */ device->setWindowCaption(L"Hello World! - Irrlicht Engine Demo"); /* Get a pointer to the VideoDriver, the SceneManager and the graphical user interface environment, so that we do not always have to write device->getVideoDriver(), device->getSceneManager(), or device->getGUIEnvironment(). */ IVideoDriver* driver = device->getVideoDriver(); ISceneManager* smgr = device->getSceneManager(); IGUIEnvironment* guienv = device->getGUIEnvironment(); /* We add a hello world label to the window, using the GUI environment. The text is placed at the position (10,10) as top left corner and (260,22) as lower right corner. */ guienv->addStaticText(L"Hello World! This is the Irrlicht Software renderer!", rect<s32>(10,10,260,22), true); /* To show something interesting, we load a Quake 2 model and display it. We only have to get the Mesh from the Scene Manager with getMesh() and add a SceneNode to display the mesh with addAnimatedMeshSceneNode(). We check the return value of getMesh() to become aware of loading problems and other errors. Instead of writing the filename sydney.md2, it would also be possible to load a Maya object file (.obj), a complete Quake3 map (.bsp) or any other supported file format. By the way, that cool Quake 2 model called sydney was modelled by Brian Collins. */ IAnimatedMesh* mesh = smgr->getMesh("/Users/dbocksteger/Desktop/test/media/sydney.md2"); if (!mesh) { device->drop(); if (!errorLabel) { errorLabel = [[UILabel alloc] init]; } errorLabel.text = @"Konnte Mesh nicht laden."; return; } IAnimatedMeshSceneNode* node = smgr->addAnimatedMeshSceneNode( mesh ); /* To let the mesh look a little bit nicer, we change its material. We disable lighting because we do not have a dynamic light in here, and the mesh would be totally black otherwise. Then we set the frame loop, such that the predefined STAND animation is used. And last, we apply a texture to the mesh. Without it the mesh would be drawn using only a color. */ if (node) { node->setMaterialFlag(EMF_LIGHTING, false); node->setMD2Animation(scene::EMAT_STAND); node->setMaterialTexture( 0, driver->getTexture("/Users/dbocksteger/Desktop/test/media/sydney.bmp") ); } /* To look at the mesh, we place a camera into 3d space at the position (0, 30, -40). The camera looks from there to (0,5,0), which is approximately the place where our md2 model is. */ smgr->addCameraSceneNode(0, vector3df(0,30,-40), vector3df(0,5,0)); /* Ok, now we have set up the scene, lets draw everything: We run the device in a while() loop, until the device does not want to run any more. This would be when the user closes the window or presses ALT+F4 (or whatever keycode closes a window). */ while(device->run()) { /* Anything can be drawn between a beginScene() and an endScene() call. The beginScene() call clears the screen with a color and the depth buffer, if desired. Then we let the Scene Manager and the GUI Environment draw their content. With the endScene() call everything is presented on the screen. */ driver->beginScene(true, true, SColor(255,100,101,140)); smgr->drawAll(); guienv->drawAll(); driver->endScene(); } /* After we are done with the render loop, we have to delete the Irrlicht Device created before with createDevice(). In the Irrlicht Engine, you have to delete all objects you created with a method or function which starts with 'create'. The object is simply deleted by calling ->drop(). See the documentation at irr::IReferenceCounted::drop() for more information. */ device->drop(); } - (void)viewDidLoad { [super viewDidLoad]; // Do any additional setup after loading the view, typically from a nib. } - (void)viewDidUnload { [super viewDidUnload]; // Release any retained subviews of the main view. } - (BOOL)shouldAutorotateToInterfaceOrientation:(UIInterfaceOrientation)interfaceOrientation { return (interfaceOrientation != UIInterfaceOrientationPortraitUpsideDown); } @end Sadly the result is just a black View in the Simulator. :( Hope here is anyone who can explain me how i draw the scene in a UIView. Furthermore I'm getting this Error: Could not load sprite bank because the file does not exist: #DefaultFont How can i fix it ?

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  • How can I repair a corrupt kernel if no others are installed?

    - by Willi Ballenthin
    I've been running Ubuntu 10.04 on my laptop for quite some time. When I went to boot it up this morning, BAM! kernel panic (which immediately lead to human panic) when loading the kernel. So I've spent much of the day troubleshooting, and my current theory is that the FS is fine, but that the kernel image may be corrupt. Let's go with this current theory for the sake of this question, as I am interested how it is done. How can I replace the kernel image if I have no bootable kernels? Can I boot to a 10.04 live CD, copy the the vmlinuz-2.6.3x... to the HD and go from there? Wouldn't I want to copy the initramfs as well, but configured for the desktop system? Can I generate this from the live CD?

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  • Locomotion-system with irregular IK

    - by htaunay
    Im having some trouble with locomtions (Unity3D asset) IK feet placement. I wouldn't call it "very bad", but it definitely isn't as smooth as the Locomotion System Examples. The strangest behavior (that is probably linked to the problem) are the rendered foot markers that "guess" where the characters next step will be. In the demo, they are smooth and stable. However, in my project, they keep flickering, as if Locomotion changed its "guess" every frame, and sometimes, the automatic defined step is too close to the previous step, or sometimes, too distant, creating a very irregular pattern. The configuration is (apparently)Identical to the human example in the demo, so I guessing the problem is my model and/or animation. Problem is, I can't figure out was it is =S Has anyone experienced the same problem? I uploaded a video of the bug to help interpreting the issue (excuse the HORRIBLE quality, I was in a hurry).

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  • Upcoming Customer WebCast: SOA 11g Database: Guide for Administrators

    - by MariaSalzberger
    The SOA infrastructure database is used by SOA Suite products like BPEL PM, BAM, BPM, Human Worklow, B2B and Mediator. A SOA administrator is involved in many different tasks like installation, upgrade, performance tuning and other administrative topics. Another important one is purging - see the posting for this: SOA Suite 11g Purging Guide. We have implemented a guide to help with thess tasks: SOA 11g Infrastructure Database: Installation, Maintenance and Administration Guide. An upcoming advisor webcast planned for Wednesday, April 11 2012 at 15:00 UK / 16:00 CET / 07:00 am Pacific / 8:00 am Mountain / 10:00 am Eastern will walk you through the guide and show some of the highligts. Registration for this webcast is available in SOA 11g Database: Guide for Administrators [ID 1422913.1]. The presentation recording can by found here after the webcast. (https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&doctype=ANNOUNCEMENT&id=740964.1) The schedule for future webcasts can be found here (https://support.oracle.com/CSP/main/article?cmd=show&type=NOT&doctype=ANNOUNCEMENT&id=740966.1)

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  • Content in Context: The right medicine for your business applications

    - by Lance Shaw
    For many of you, your companies have already invested in a number of applications that are critical to the way your business is run. HR, Payroll, Legal, Accounts Payable, and while they might need an upgrade in some cases, they are all there and handling the lifeblood of your business. But are they really running as efficiently as they could be? For many companies, the answer is no. The problem has to do with the important information caught up within documents and paper. It’s everywhere except where it truly needs to be – readily available right within the context of the application itself. When the right information cannot be easily found, business processes suffer significantly. The importance of this recently struck me when I recently went to meet my new doctor and get a routine physical. Walking into the office lobby, I couldn't help but notice rows and rows of manila folders in racks from floor to ceiling, filled with documents and sensitive, personal information about various patients like myself.  As I looked at all that paper and all that history, two things immediately popped into my head.  “How do they find anything?” and then the even more alarming, “So much for information security!” It sure looked to me like all those documents could be accessed by anyone with a key to the building. Now the truth is that the offices of many general practitioners look like this all over the United States and the world.  But it had me thinking, is the same thing going on in just about any company around the world, involving a wide variety of important business processes? Probably so. Think about all the various processes going on in your company right now. Invoice payments are being processed through Accounts Payable, contracts are being reviewed by Procurement, and Human Resources is reviewing job candidate submissions and doing background checks. All of these processes and many more like them rely on access to forms and documents, whether they are paper or digital. Now consider that it is estimated that employee’s spend nearly 9 hours a week searching for information and not finding it. That is a lot of very well paid employees, spending more than one day per week not doing their regular job while they search for or re-create what already exists. Back in the doctor’s office, I saw this trend exemplified as well. First, I had to fill out a new patient form, even though my previous doctor had transferred my records over months previously. After filling out the form, I was later introduced to my new doctor who then interviewed me and asked me the exact same questions that I had answered on the form. I understand that there is value in the interview process and it was great to meet my new doctor, but this simple process could have been so much more efficient if the information already on file could have been brought directly together with the new patient information I had provided. Instead of having a highly paid medical professional re-enter the same information into the records database, the form I filled out could have been immediately scanned into the system, associated with my previous information, discrepancies identified, and the entire process streamlined significantly. We won’t solve the health records management issues that exist in the United States in this blog post, but this example illustrates how the automation of information capture and classification can eliminate a lot of repetitive and costly human entry and re-creation, even in a simple process like new patient on-boarding. In a similar fashion, by taking a fresh look at the various processes in place today in your organization, you can likely spot points along the way where automating the capture and access to the right information could be significantly improved. As you evaluate how content-process flows through your organization, take a look at how departments and regions share information between the applications they are using. Business applications are often implemented on an individual department basis to solve specific problems but a holistic approach to overall information management is not taken at the same time. The end result over the years is disparate applications with separate information repositories and in many cases these contain duplicate information, or worse, slightly different versions of the same information. This is where Oracle WebCenter Content comes into the story. More and more companies are realizing that they can significantly improve their existing application processes by automating the capture of paper, forms and other content. This makes the right information immediately accessible in the context of the business process and making the same information accessible across departmental systems which has helped many organizations realize significant cost savings. Here on the Oracle WebCenter team, one of our primary goals is to help customers find new ways to be more effective, more cost-efficient and manage information as effectively as possible. We have a series of three webcasts occurring over the next few weeks that are focused on the integration of enterprise content management within the context of business applications. We hope you will join us for one or all three and that you will find them informative. Click here to learn more about these sessions and to register for them. There are many aspects of information management to consider as you look at integrating content management within your business applications. We've barely scratched the surface here but look for upcoming blog posts where we will discuss more specifics on the value of delivering documents, forms and images directly within applications like Oracle E-Business Suite, PeopleSoft Enterprise, JD Edwards Enterprise One, Siebel CRM and many others. What do you think?  Are your important business processes as healthy as they can be?  Do you have any insights to share on the value of delivering content directly within critical business processes? Please post a comment and let us know the value you have realized, the lessons learned and what specific areas you are interested in.

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  • What *exactly* gets screwed when I kill -9 or pull the power?

    - by Mike
    Set-Up I've been a programmer for quite some time now but I'm still a bit fuzzy on deep, internal stuff. Now. I am well aware that it's not a good idea to either: kill -9 a process (bad) spontaneously pull the power plug on a running computer or server (worse) However, sometimes you just plain have to. Sometimes a process just won't respond no matter what you do, and sometimes a computer just won't respond, no matter what you do. Let's assume a system running Apache 2, MySQL 5, PHP 5, and Python 2.6.5 through mod_wsgi. Note: I'm most interested about Mac OS X here, but an answer that pertains to any UNIX system would help me out. My Concern Each time I have to do either one of these, especially the second, I'm very worried for a period of time that something has been broken. Some file somewhere could be corrupt -- who knows which file? There are over 1,000,000 files on the computer. I'm often using OS X, so I'll run a "Verify Disk" operation through the Disk Utility. It will report no problems, but I'm still concerned about this. What if some configuration file somewhere got screwed up. Or even worse, what if a binary file somewhere is corrupt. Or a script file somewhere is corrupt now. What if some hardware is damaged? What if I don't find out about it until next month, in a critical scenario, when the corruption or damage causes a catastrophe? Or, what if valuable data is already lost? My Hope My hope is that these concerns and worries are unfounded. After all, after doing this many times before, nothing truly bad has happened yet. The worst is I've had to repair some MySQL tables, but I don't seem to have lost any data. But, if my worries are not unfounded, and real damage could happen in either situation 1 or 2, then my hope is that there is a way to detect it and prevent against it. My Question(s) Could this be because modern operating systems are designed to ensure that nothing is lost in these scenarios? Could this be because modern software is designed to ensure that nothing lost? What about modern hardware design? What measures are in place when you pull the power plug? My question is, for both of these scenarios, what exactly can go wrong, and what steps should be taken to fix it? I'm under the impression that one thing that can go wrong is some programs might not have flushed their data to the disk, so any highly recent data that was supposed to be written to the disk (say, a few seconds before the power pull) might be lost. But what about beyond that? And can this very issue of 5-second data loss screw up a system? What about corruption of random files hiding somewhere in the huge forest of files on my hard drives? What about hardware damage? What Would Help Me Most Detailed descriptions about what goes on internally when you either kill -9 a process or pull the power on the whole system. (it seems instant, but can someone slow it down for me?) Explanations of all things that could go wrong in these scenarios, along with (rough of course) probabilities (i.e., this is very unlikely, but this is likely)... Descriptions of measures in place in modern hardware, operating systems, and software, to prevent damage or corruption when these scenarios occur. (to comfort me) Instructions for what to do after a kill -9 or a power pull, beyond "verifying the disk", in order to truly make sure nothing is corrupt or damaged somewhere on the drive. Measures that can be taken to fortify a computer setup so that if something has to be killed or the power has to be pulled, any potential damage is mitigated. Thanks so much!

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  • Language Design: Are languages like phyton and coffescript really more comprehendable?

    - by kittensatplay
    the "Verbally Readable !== Quicker Comprehension" arguement on http://ryanflorence.com/2011/case-against-coffeescript/ is really potent and interesting. i and im sure other would be very interested in evidence arguing against this. there's clear evidence for this and i believe it. ppl naturally think in images, not words, so we should be designing languages dissimilar to human language like english, french, whatever. being "readable" is quicker comprehension. most articles on wikipedia are not readable as they are long, boring, dry, sluggish, very very wordy, and because wikipedia documents a ton of info, is not especially helpful when compared to much more helpful sites with more practical, useful, and relevant info. but languages like phyton and coffescript are "verbally readable" in that they are closer to the english language syntax, and programming firstly and mainly in python, im not so sure this is really a good thing. the second interesting argument is that coffeescript is an intermediator so thereby another step between to ends, which may increase chances of bugs. while coffeescript has other practical benefits, this question is focused specifically on evidence showing support for the counter-case of language "readability"

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  • Snooker Android Application [closed]

    - by Rzarect
    I am working currently on my final year project / dissertation for the university and I have a "crazy" idea for it. I was thinking of designing an android app for Snooker players, different bars or tournaments, an app that will use the mobile camera to detect every movement and change on the table and in the same time will keep the score for the players without any human input. I want to know if it is an impossible thing. If it is plausible I really need some ideas, advices from where to start. I got to say that I have some experience in Android development and I already started to read a lot of articles, projects about the shape detection, color detection and edge detection.

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  • How i can sign and/or group a specific set of vertices in a 3D file container like OBJ ? - in Blender

    - by user827992
    I would like to export a 3D model with each part having a name or a label if you will. For example i would like to export a model of an human body and name each part in specifics vertex groups like: left hand, right hand, right foot, head, ears, ... and you got the idea; so i can have a single 3D model that i can explode in various parts if needed. If there is a better technique about how to mark vertex groups in a 3D file please share your solution. As 3D editor i use Blender.

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  • Coherence Data Guarantees for Data Reads - Basic Terminology

    - by jpurdy
    When integrating Coherence into applications, each application has its own set of requirements with respect to data integrity guarantees. Developers often describe these requirements using expressions like "avoiding dirty reads" or "making sure that updates are transactional", but we often find that even in a small group of people, there may be a wide range of opinions as to what these terms mean. This may simply be due to a lack of familiarity, but given that Coherence sits at an intersection of several (mostly) unrelated fields, it may be a matter of conflicting vocabularies (e.g. "consistency" is similar but different in transaction processing versus multi-threaded programming). Since almost all data read consistency issues are related to the concept of concurrency, it is helpful to start with a definition of that, or rather what it means for two operations to be concurrent. Rather than implying that they occur "at the same time", concurrency is a slightly weaker statement -- it simply means that it can't be proven that one event precedes (or follows) the other. As an example, in a Coherence application, if two client members mutate two different cache entries sitting on two different cache servers at roughly the same time, it is likely that one update will precede the other by a significant amount of time (say 0.1ms). However, since there is no guarantee that all four members have their clocks perfectly synchronized, and there is no way to precisely measure the time it takes to send a given message between any two members (that have differing clocks), we consider these to be concurrent operations since we can not (easily) prove otherwise. So this leads to a question that we hear quite frequently: "Are the contents of the near cache always synchronized with the underlying distributed cache?". It's easy to see that if an update on a cache server results in a message being sent to each near cache, and then that near cache being updated that there is a window where the contents are different. However, this is irrelevant, since even if the application reads directly from the distributed cache, another thread update the cache before the read is returned to the application. Even if no other member modifies a cache entry prior to the local near cache entry being updated (and subsequently read), the purpose of reading a cache entry is to do something with the result, usually either displaying for consumption by a human, or by updating the entry based on the current state of the entry. In the former case, it's clear that if the data is updated faster than a human can perceive, then there is no problem (and in many cases this can be relaxed even further). For the latter case, the application must assume that the value might potentially be updated before it has a chance to update it. This almost aways the case with read-only caches, and the solution is the traditional optimistic transaction pattern, which requires the application to explicitly state what assumptions it made about the old value of the cache entry. If the application doesn't want to bother stating those assumptions, it is free to lock the cache entry prior to reading it, ensuring that no other threads will mutate the entry, a pessimistic approach. The optimistic approach relies on what is sometimes called a "fuzzy read". In other words, the application assumes that the read should be correct, but it also acknowledges that it might not be. (I use the qualifier "sometimes" because in some writings, "fuzzy read" indicates the situation where the application actually sees an original value and then later sees an updated value within the same transaction -- however, both definitions are roughly equivalent from an application design perspective). If the read is not correct it is called a "stale read". Going back to the definition of concurrency, it may seem difficult to precisely define a stale read, but the practical way of detecting a stale read is that is will cause the encompassing transaction to roll back if it tries to update that value. The pessimistic approach relies on a "coherent read", a guarantee that the value returned is not only the same as the primary copy of that value, but also that it will remain that way. In most cases this can be used interchangeably with "repeatable read" (though that term has additional implications when used in the context of a database system). In none of cases above is it possible for the application to perform a "dirty read". A dirty read occurs when the application reads a piece of data that was never committed. In practice the only way this can occur is with multi-phase updates such as transactions, where a value may be temporarily update but then withdrawn when a transaction is rolled back. If another thread sees that value prior to the rollback, it is a dirty read. If an application uses optimistic transactions, dirty reads will merely result in a lack of forward progress (this is actually one of the main risks of dirty reads -- they can be chained and potentially cause cascading rollbacks). The concepts of dirty reads, fuzzy reads, stale reads and coherent reads are able to describe the vast majority of requirements that we see in the field. However, the important thing is to define the terms used to define requirements. A quick web search for each of the terms in this article will show multiple meanings, so I've selected what are generally the most common variations, but it never hurts to state each definition explicitly if they are critical to the success of a project (many applications have sufficiently loose requirements that precise terminology can be avoided).

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  • What is Pseudocode?

    - by Jae
    I've seen a lot of mentions of Pseudocode lately, on this site and others. But I don't get it: What is Pseudocode? For example, the Wikipedia article below says "It uses the structural conventions of a programming language, but is intended for human reading rather than machine reading." Does this mean that it isn't actually used to make programs? Why is it used? How is it used? Is it considered a Programming Language? See the above Wikipedia quote. Is it commonly known/used? Anything else... I honestly don't know where to start with this. I have Googled it and I've seen the Wikipedia article on the topic, but I still don't fully understand what it is.

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  • New customer references for Exadata-based projects

    - by Javier Puerta
    Milletech Systems, Inc. shows a large state university how to improve query response times 15-fold using its grant management solution built on Oracle’s Extreme Performance Infrastructure. Read More. Ação Informática helped Valdecard realize a 15-Fold Improvement in Fleet-Management and Benefit Card Data Processing using Oracle Exadata Machine. Read More. Neusoft deployed Benxi Municipal Human Resources and Social Security Bureau’s cloud-based database platform to process social insurance payments 50-times faster using Oracle Exadata Database Machine. Read More.

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  • What are the benefits vs costs of comment annotation in PHP?

    - by Patrick
    I have just started working with symfony2 and have run across comment annotations. Although comment annotation is not an inherent part of PHP, symfony2 adds support for this feature. My understanding of commenting is that it should make the code more intelligible to the human. The computer shouldn't care what is in comments. What benefits come from doing this type of annotation versus just putting a command in the normal PHP code? ie- /** * @Route("/{id}") * @Method("GET") * @ParamConverter("post", class="SensioBlogBundle:Post") * @Template("SensioBlogBundle:Annot:post.html.twig", vars={"post"}) * @Cache(smaxage="15") */ public function showAction(Post $post) { }

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  • Implementing a Custom Coherence PartitionAssignmentStrategy

    - by jpurdy
    A recent A-Team engagement required the development of a custom PartitionAssignmentStrategy (PAS). By way of background, a PAS is an implementation of a Java interface that controls how a Coherence partitioned cache service assigns partitions (primary and backup copies) across the available set of storage-enabled members. While seemingly straightforward, this is actually a very difficult problem to solve. Traditionally, Coherence used a distributed algorithm spread across the cache servers (and as of Coherence 3.7, this is still the default implementation). With the introduction of the PAS interface, the model of operation was changed so that the logic would run solely in the cache service senior member. Obviously, this makes the development of a custom PAS vastly less complex, and in practice does not introduce a significant single point of failure/bottleneck. Note that Coherence ships with a default PAS implementation but it is not used by default. Further, custom PAS implementations are uncommon (this engagement was the first custom implementation that we know of). The particular implementation mentioned above also faced challenges related to managing multiple backup copies but that won't be discussed here. There were a few challenges that arose during design and implementation: Naive algorithms had an unreasonable upper bound of computational cost. There was significant complexity associated with configurations where the member count varied significantly between physical machines. Most of the complexity of a PAS is related to rebalancing, not initial assignment (which is usually fairly simple). A custom PAS may need to solve several problems simultaneously, such as: Ensuring that each member has a similar number of primary and backup partitions (e.g. each member has the same number of primary and backup partitions) Ensuring that each member carries similar responsibility (e.g. the most heavily loaded member has no more than one partition more than the least loaded). Ensuring that each partition is on the same member as a corresponding local resource (e.g. for applications that use partitioning across message queues, to ensure that each partition is collocated with its corresponding message queue). Ensuring that a given member holds no more than a given number of partitions (e.g. no member has more than 10 partitions) Ensuring that backups are placed far enough away from the primaries (e.g. on a different physical machine or a different blade enclosure) Achieving the above goals while ensuring that partition movement is minimized. These objectives can be even more complicated when the topology of the cluster is irregular. For example, if multiple cluster members may exist on each physical machine, then clearly the possibility exists that at certain points (e.g. following a member failure), the number of members on each machine may vary, in certain cases significantly so. Consider the case where there are three physical machines, with 3, 3 and 9 members each (respectively). This introduces complexity since the backups for the 9 members on the the largest machine must be spread across the other 6 members (to ensure placement on different physical machines), preventing an even distribution. For any given problem like this, there are usually reasonable compromises available, but the key point is that objectives may conflict under extreme (but not at all unlikely) circumstances. The most obvious general purpose partition assignment algorithm (possibly the only general purpose one) is to define a scoring function for a given mapping of partitions to members, and then apply that function to each possible permutation, selecting the most optimal permutation. This would result in N! (factorial) evaluations of the scoring function. This is clearly impractical for all but the smallest values of N (e.g. a partition count in the single digits). It's difficult to prove that more efficient general purpose algorithms don't exist, but the key take away from this is that algorithms will tend to either have exorbitant worst case performance or may fail to find optimal solutions (or both) -- it is very important to be able to show that worst case performance is acceptable. This quickly leads to the conclusion that the problem must be further constrained, perhaps by limiting functionality or by using domain-specific optimizations. Unfortunately, it can be very difficult to design these more focused algorithms. In the specific case mentioned, we constrained the solution space to very small clusters (in terms of machine count) with small partition counts and supported exactly two backup copies, and accepted the fact that partition movement could potentially be significant (preferring to solve that issue through brute force). We then used the out-of-the-box PAS implementation as a fallback, delegating to it for configurations that were not supported by our algorithm. Our experience was that the PAS interface is quite usable, but there are intrinsic challenges to designing PAS implementations that should be very carefully evaluated before committing to that approach.

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  • HTG Explains: What is DNS?

    - by Chris Hoffman
    Did you know you could be connected to facebook.com – and see facebook.com in your web browser’s address bar – while not actually being connected to Facebook’s real website? To understand why, you’ll need to know a bit about DNS. DNS underpins the world wide web we use every day. It works transparently in the background, converting human-readable website names into computer-readable numerical IP addresses. Image Credit: Jemimus on Flickr How To Switch Webmail Providers Without Losing All Your Email How To Force Windows Applications to Use a Specific CPU HTG Explains: Is UPnP a Security Risk?

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  • Programming to ANSI standards (for engineering)

    - by Jake
    I am currently tasked to write a software to help engineers design standard compliant designs. If there is a bad design, software will report an error or warning. Maybe it's just me, but anyone who has done this should be familiar with the massive amounts of ANSI standards tables like this one: http://en.wikipedia.org/wiki/Nominal_Pipe_Size Computers are, as its name suggest, computing machines, not lookup machines. I feel that feeding formulas into computers and churning out standard compliant designs is much more efficient than doing memory intensive data lookups that are prone to human input errors and susceptible to "data updates". I actually think that there are formulas to calculate all those numbers, but nobody so far could give me that information. Anyone been through this before? What is THE best approach to this? Thanks for sharing.

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