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• Are log records removed from ldf file for rollbacks?

  - by TiborKaraszi

  Seems like a simple enough question, right? This question (but more targeted, read on) was raised in an MCT forum. While the discussion was on-going and and I tried to come up with answers, I realized that this question are really several questions. First, what is a rollback? I can see three different types of rollbacks (there might be more, of course): Regular rollback, as in ROLLBACK TRAN (or lost/terminated connection) Rollback done by restore recovery. I.e., end-time of backup included some transaciton...(read more)

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• Misconceptions about purely functional languages?

  - by Giorgio

  I often encounter the following statements / arguments: Pure functional programming languages do not allow side effects (and are therefore of little use in practice because any useful program does have side effects, e.g. when it interacts with the external world). Pure functional programming languages do not allow to write a program that maintains state (which makes programming very awkward because in many application you do need state). I am not an expert in functional languages but here is what I have understood about these topics until now. Regarding point 1, you can interact with the environment in purely functional languages but you have to explicitly mark the code (functions) that introduces them (e.g. in Haskell by means of monadic types). Also, AFAIK computing by side effects (destructively updating data) should also be possible (using monadic types?) but is not the preferred way of working. Regarding point 2, AFAIK you can represent state by threading values through several computation steps (in Haskell, again, using monadic types) but I have no practical experience doing this and my understanding is rather vague. So, are the two statements above correct in any sense or are they just misconceptions about purely functional languages? If they are misconceptions, how did they come about? Could you write a (possibly small) code snippet illustrating the Haskell idiomatic way to (1) implement side effects and (2) implement a computation with state?

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• Changes to talk/ytalk or alternative chat in the Linux terminal

  - by cascaval

  While looking for a piece of software that provides chat between 2 Linux server users logged in the terminal, I tried talk/ytalk. Unfortuntaley it provides chat between users on separate walls (each user has its own wall) and the messages lack timestamps. Is it possible to set it up so that at least timestamps are provided? Alternatively, is there any other software that could provide one wall on which users write messages prepended with time? Simple chat with messages listed in the order of submission would be ideal: 13:05:48 [bridgekeeper@...]: What is the air-speed velocity of an unladen swallow? 13:06:28 [cascaval@...]: What do you mean? An African or European swallow? I already tried wall and write but they don't fit the bill. OS: Debian 6.0

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• RPi and Java Embedded GPIO: Hooking Up Your Wires for Java

  - by hinkmond

  So, you bought your blue jumper wires, your LEDs, your resistors, your breadboard, and your fill of Fry's for the day. How do you hook this cool stuff up to write Java code to blink them LEDs? I'll step you through it. First look at that pinout diagram of the GPIO header that's on your RPi. Find the pins in the corner of your RPi board and make sure to orient it the right way. The upper left corner pin should have the characters "P1" next to it on the board. That pin next to "P1" is your Pin #1 (in the diagram). Then, you can start counting left, right, next row, left, right, next row, left, right, and so on: Pins # 1, 2, next row, 3, 4, next row, 5, 6, and so on. Take one blue jumper wire and connect to Pin # 3 (GPIO0). Connect the other end to a resistor and then the other end of the resistor into the breadboard. Each row of grouped-together holes on a breadboard are connected, so plug in the short-end of a common cathode LED (long-end of a common anode LED) into a hole that is in the same grouping as where the resistor is plugged in. Then, connect the other end of the LED back to Pin # 6 (GND) on the RPi GPIO header. Now you have your first LED connected ready for you to write some Java code to turn it on and off. (As, extra credit you can connect 7 other LEDs the same way to with one lead to Pins # 5, 7, 11, 13, 15, 19 & 21). Whew! That wasn't so bad, was it? Next blog post on this thread will have some Java source code for you to try... Hinkmond

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• perfmon reporting higher IOPs than possible?

  - by BlueToast

  We created a monitoring report for IOPs on performance counters using Disk reads/sec and Disk writes/sec on four servers (physical boxes, no virtualization) that have 4x 15k 146GB SAS drives in RAID10 per server, set to check and record data every 1 second, and logged for 24 hours before stopping reports. These are the results we got: Server1 Maximum disk reads/sec: 4249.437 Maximum disk writes/sec: 4178.946 Server2 Maximum disk reads/sec: 2550.140 Maximum disk writes/sec: 5177.821 Server3 Maximum disk reads/sec: 1903.300 Maximum disk writes/sec: 5299.036 Server4 Maximum disk reads/sec: 8453.572 Maximum disk writes/sec: 11584.653 The average disk reads and writes per second were generally low. I.e. for one particular server it was like average 33 writes/sec, but when monitoring in real-time it would often spike up to several hundreds and also sometimes into the thousands. Could someone explain to me why these numbers are significantly higher than theoretical calculations assuming each drive can do 180 IOPs? Additional details (RAID card): HP Smart Array P410i, Total cache size of 1GB, Write cache is disabled, Array accelerator cache ratio is 25% read and 75% write

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• Can Clojure's thread-based agents handle c10k performance?

  - by elliot42

  I'm writing a c10k-style service and am trying to evaluate Clojure's performance. Can Clojure agents handle this scale of concurrency with its thread-based agents? Other high performance systems seem to be moving towards async-IO/events/greenlets, albeit at a seemingly higher complexity cost. Suppose there are 10,000 clients connected, sending messages that should be appended to 1,000 local files--the Clojure service is trying to write to as many files in parallel as it can, while not letting any two separate requests mangle the same single file by writing at the same time. Clojure agents are extremely elegant conceptually--they would allow separate files to be written independently and asynchronously, while serializing (in the database sense) multiple requests to write to the same file. My understanding is that agents work by starting a thread for each operation (assume we are IO-bound and using send-off)--so in this case is it correct that it would start 1,000+ threads? Can current-day systems handle this number of threads efficiently? Most of them should be IO-bound and sleeping most of the time, but I presume there would still be a context-switching penalty that is theoretically higher than async-IO/event-based systems (e.g. Erlang, Go, node.js). If the Clojure solution can handle the performance, it seems like the most elegant thing to code. However if it can't handle the performance then something like Erlang or Go's lightweight processes might be preferable, since they are designed to have tens of thousands of them spawned at once, and are only moderately more complex to implement. Has anyone approached this problem in Clojure or compared to these other platforms? (Thanks for your thoughts!)

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• 2011 Tech Goal Review

  - by kerry

  A year ago I wrote a post listing my professional goals for 2011.  I thought I would review them and see how I did. Release an Android app to the marketplace – Didn’t do it.  In fact, haven’t really touched Android much since I wrote that.  I still have some ideas but am not sure if I will get around to it. Contribute free software to the community – I did do this.  I have been collaborating with others via github more lately. Regularly attend a user group meetings outside of Java – Did not do this.  Family life being what it is makes this not that much of a priority right now. Obtain the Oracle Certified Web Developer Certification – Did not do this.  This is not much of a priority to me any more. Learn scala – I am about 50/50 on this one.  I read a few scala books but did not write an actual application. Write an app using JSF – Did not do this.  Still interested. Present at a user group meeting – I did a Maven presentation at the Java user group. Use git more, and more effectively – Definitely did this.  Using it on a daily basis now. Overall, I got about halfway on my goals.  It’s not too bad since I did do a few things that weren’t on my list. Learned to develop applications using GWT and deploy them to Google App Engine Converted one of my sites from PHP to Ruby / Sinatra (learning to use it in the process) Studied up on the HTML 5 features and did a lot of Javascript development

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• Create a share on iscsi drive in Windows Server 2012

  - by Crash893

  I am brand new to server administration but I don't belive im trying to do anything to exotic I have a windows server 2012 (standard) and a drobo 800i My goal is to setup company shares on the iscsi target I have setup on the drobo So far I have: initialized the iscsi and connected made the iscsi disk read/write(it default started as read only) formatted and mounted it (as drive E:) from the server local desktop I can see and write files to the E:\ drive in shares wizard I do not see it as a volume option when I view the volumes window I see (e: drobo Fixed 16tb 16tb) I'm new to everything but I would think since its a mounted drive I should be able to share a folder on it but it appears its not that straight forward suggestions?

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• Do PHP-FPM (and other PHP handlers) need execute permissions on the PHP files they're serving?

  - by Andrew Cheong

  I read in a post at Server Fault that PHP-FPM needs execute permissions. However, the answer in When creating a website, what permissions and directory structure? only grants read and write permissions to PHP-FPM. Maybe I don't quite understand how PHP handlers (or CGI in general) work, but the two claims seem contradictory to me. As I understand, when Apache / Nginx gets a request for foobar.php, it "passes" the file to an appropriate handler. That is, I imagine it's as if www-root (or apache or whomever the webserver's running as) were to run some command, /usr/sbin/php-fpm foobar.php Actually, no, that's naive, I just realized. PHP-FPM must be a running instance (if it's to be performant, and cache, etc.), so probably PHP-FPM is just being told, "Hey, quick, process this file for me!" In either case, I don't see why execute permissions are necessary. It's not like the webserver needs to literally execute the file, i.e. ./foobar.php Is the Server Fault answer simply mistaken?

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• VPS Server OS differences

  - by silvercover

  I have two VPS servers. one of them is running Linux and the other is Windows one. I've uploaded same file to their public_html folders and could see them in my browser via static IP address of each one like http://178.63.165.178/getorder/file.xml and http://178.63.165.178/getorder/file.xml. On the other side there is a device called SMSPrinter that configured to read those XML files using GPRS and need static IP address to reach destination server. unfortunately this device can only read file from windows server and could not reach the file on Linux server. There is no note in this device manual suggesting Windows server or specific OS! I've also set file permission on Linux server to 777 to have no limitation. what could be the cause of our problem? Thanks.

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• C# Simple Twitter Update

  - by mroberts

  For what it's worth a simple twitter update. using System; using System.IO; using System.Net; using System.Text; namespace Server.Actions { public class TwitterUpdate { public string Body { get; set; } public string Login { get; set; } public string Password { get; set; } public override void Execute() { try { //encode user name and password string creds = Convert.ToBase64String(Encoding.ASCII.GetBytes(string.Format("{0}:{1}", this.Login, this.Password))); //encode tweet byte[] tweet = Encoding.ASCII.GetBytes("status=" + this.Body); //setup request HttpWebRequest request = (HttpWebRequest)WebRequest.Create("http://twitter.com/statuses/update.xml"); request.Method = "POST"; request.ServicePoint.Expect100Continue = false; request.Headers.Add("Authorization", string.Format("Basic {0}", creds)); request.ContentType = "application/x-www-form-urlencoded"; request.ContentLength = tweet.Length; //write to stream Stream reqStream = request.GetRequestStream(); reqStream.Write(tweet, 0, tweet.Length); reqStream.Close(); //check response HttpWebResponse response = (HttpWebResponse)request.GetResponse(); //... } catch (Exception e) { //... } } } }

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• How do I query the gvfs metadata for a specific attribute?

  - by Mathieu Comandon

  A nice feature in evince is that when you close the program and later reopen the same pdf, it automatically jumps to the page you were reading. The problem I have is that I often read ebooks on several computers and I have to find were I was on the last computer I was reading the pdf. I think syncing these bookmarks in UbuntuOne would be a killer feature for people like me who read pdfs on different computers. By investigating a bit, I found where evince was storing this data, it's in the gvfs metadata and it can be accessed for a particular document by typing gvfs-ls -a "metadata::evince::page" myEbook.pdf Rather that querying a particular file, I'd like to query the whole metadata file (located in ~/.local/share/gvfs-metadata/home for the home directory) for any file where this particular attribute is set to some value. The biggest issue is that gvfs metadata and stored in binary files and we all know it's not easy to get something out of a binary file. So, do you know any way to query the gvfs metadata for some attribute?

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• Creating floppy drive special devices under Quantal

  - by JCCyC

  First, I'd like for the various special devices for different floppy capacities (like /dev/fd0u720 etc.) to be available. I tried to adapt some udev rules I found online. I tried this, which I saved as /etc/udev/rules.d/70-persistent-floppy.rules: # change floppy device ownership and permissions # default permissions are 640, which prevents group users from having write access # first fix primary devices (/dev/fd0, /dev/fd1, etc.) # also change group ownership from disk to floppy SUBSYSTEM=="block", KERNEL=="fd[0-9]*", GROUP="floppy", MODE="0660" # next recreate secondary devices (/dev/fd0u720, /dev/fd0u1440, etc.) SUBSYSTEM=="block", KERNEL=="fd[0-9]*", ACTION=="add", RUN+="create_floppy_devices -c -t $attr{cmos} -m %M -M 0660 -G floppy $root/%k" But to no avail. It seems the create_floppy_devices script isn't provided with 12.10. How do I obtain it? Second: I'm using MATE, and whenever I log in I get a message box saying it tried to mount the drive but failed. How do I disable this? Third (which is probably related to the second): Whenever there's a disk in the drive, the motor won't stop spinning. If I do a mdir of it, after it returns, the motor stops, and then starts again. I suspect there's some process in MATE doing this. UPDATE: For CentOS 6 (who does have a create_floppy_devices program) the following rules file worked. Saved as /etc/udev/rules.d/98-floppy.rules: # change floppy device ownership and permissions # default permissions are 640, which prevents group users from having write access # first fix primary devices (/dev/fd0, /dev/fd1, etc.) # also change group ownership from disk to floppy KERNEL=="fd[0-9]*", GROUP="floppy", MODE="0660" # next recreate secondary devices (/dev/fd0u720, /dev/fd0u1440, etc.) # drive A: is type 4 (1.44MB) - add other lines for other drives KERNEL=="fd0*", ACTION=="add", RUN+="/lib/udev/create_floppy_devices -c -t 4 -m %M -M 0660 -G floppy $root/%k"

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• How do install Ubuntu from a USB stick?

  - by Sophia

  When I go to the boot menu on my computer and select USB stick, the screen goes black and there comes a flickering underline. Like I could write something. But I can't. Whatever I push, nothing happens. Except the PrintScrn/SysRq button. When I push it, mu computer beeps. I get no choose menu. Nothing. I found out the usb stick is in msdos format. So what format should I use and how can I format it? I am not a computer geek who knows everything. I'm just a beginner. And only 16 years old. I've got a new problem. The screen isn't black anymore. Now there comes an error message: SYSLINUX 4.04 CHS 20110518 Copyright (C) 1994-2011 H.Peter Anvin et al ERROR:No configurationfile found No DEFAULT or UI configuration directive found! boot: And when I write something: boot:example Could not find kernel image:example boot: Why does this fail all the time? ps. I'm using Ubuntu Oneiric 11.10.

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• Criteria for selecting timeout value?

  - by stijn

  Situation: a piece of software reads frames of data from a file in a seperate thread and puts it on a queue, emptied by another thread. That second thread periodically checks on the queue and fails rather gracefully, by showing an error message stating the read timed out, if no data is available within a certain amount of time. Initially this timeout was set to 200mSec. There was no real reasoning behind that constant though, but it worked fine. We measured on a couple of machines and for large data frames, larger than what would be used by customers, a read took like 20mSec whith no other load on the machine. However one customer now gets timeout errors now and then (on the second try all is fine, probably the file is in cache or the virus scanner leaves it alone). The programmers are like 'well, yeah, but that customer's machine is full of cruft, virus scanners, tons of unneeded background processes etc'. Of course the customer is like 'hey this should just work, shouldn't it'? While the programers have a point, since the software is heavy enough to validate the need for a dedicated machine, that does not make the customer happy. Increasing the timeout to 2 seconds, for example, solves the problem. But I'd like to make a proper decision now instead of just randomly pick some magic constant that is probably ok in 99% of cases. What criteria should be used for that? We could just pick a large number, but that feels wrong. (and then we end up with a program that has the horrible bahaviour of hanging when trying to read from a disconnected drive for instance, whereas we'd rather make it show an error right away). Or we could make the timeout value a user setting, but then we need to ducument it clearly and even then not all customers are tech savy enough to really understand what it does. Or we could try and wait until another customer reports timeouts and increase the value again. And again. Until we find something ok for 99.99% of the cases.. Any good practice for this type of situation?

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• Almost Realtime Data and Web application

  - by Chris G.

  I have a computer that is recording 100 different data points into an OPC server. I've written a simple OPC client that can read all of this data. I have a front-end website on a different network that I would like to consume this data. I could easily set the OPC client to send the data to a SQL server and the website could read from it, but that would be a lot of writes. If I wanted the data to be updated every 10 seconds I'd be writing to the database every 10 seconds. (I could probably just serialize the 100 points to get 1 write / 10 seconds but that would also limit my ability to search the data later). This solution wouldn't scale very well. If I had 100 of these computers the situation would quickly grow out of hand. Obviously I am well out of my league here and I have no experience with working with a large amount of data like this. What are my options and what should I research?

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• DataSets and XML - The Simplistic Approach

  One of the first ways I learned how to read xml data from external data sources was by using a DataSet’s ReadXML function. This function takes file path for an XML document and then converts it to a Dataset. This functionality is great when you need a simple way to process an XML document.  In addition the DataSet object also offers a simple way to save data in an xml format by using the WriteXML function. This function saves the current data in the DataSet to an XML file to be used later. DataSet ds  = New DataSet();String filePath = “http://www.yourdomain.com/someData.xml”;String fileSavePath = “C:\Temp\Test.xml”//Read file for this locationds.readxml(filePath);//Save file to this locationds.writexml(fileSavePath); I have used the ReadXML function before when consuming data from external Rss feeds to display on one of my sites.  It allows me to quickly pull in data from external sites with little to no processing. Example site: MyCreditTech.com

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• Book Review: Expert Cube Development with Microsoft SQL Server 2008 Analysis Services

  - by Greg Low

  I spent last week on campus in Redmond with the SQL Server Analysis Services Maestro program. It was great to have a chance to focus on SSAS for a week. As part of that, I did quite a bit of reading as I had quite a bit of travelling time. Ironically, I re-read a few books. The first was Marco Russo, Alberto Ferrari and Chris Webb's book Expert Cube Development with Microsoft SQL Server 2008 Analysis Services . I've often told BI classes that I've been teaching that this is a really good book and...(read more)

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• HALEVT troubleshooting: VFAT usb storage device gets mounted with root:root user:group

  - by Nova deViator

  Hi, i'm banging my head for number of days around this problem. using Halevt for automounting, everything mostly works, but the only thing is that Halevt mounts external USB storage devices as root. So, as user i cannot write to files on them. Halevt gets run as halevt user on boot through /etc/init.d script. This is Ubuntu Lucid with Awesome WM. No GDM. Running halevt as user seem to not work (halevt runs but doesn't respond on Insert) I know HAL is deprecated and removed and i should probably write my own UDEV rules, but until then it seems there must a be simple hack that enables mounting VFAT/NTFS devices with specific uid/gid. this question/answer helps a lot, but not specifically to the above.

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• Aliasing resellers domain to primary domain

  - by Ashkan Mobayen Khiabani

  I have designed a website that accepts re-sellers and actually the concept of this website is having local re-sellers for each province (or should we say branches). I have designed this website in a way that anybody who has a domain, can point to our website (a record or cname). well most of the website content are the same, the only difference is that re-sellers website doesn't have some items on the main menu and may have some small descriptions of their own branch in some pages. I read that Google may ban websites with duplicate content (or which are significantly similar). I want to know will this be a problem for me? If yes, what else can I do? we have had considered asking our reseller to use iframe that loads our website but wanted that each reseller can have its own SEO and try harder but what I read about this duplicate thing worries me.

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• WebLogic Application Server: free for developers!

  - by Bruno.Borges

  Great news! Oracle WebLogic Server is now free for developers! What does this mean for you? That you as a developer are permited to: "[...] deploy the programs only on your single developer desktop computer (of any type, including physical, virtual or remote virtual), to be used and accessed by only (1) named developer." But the most interesting part of the license change is this one: "You may continue to develop, test, prototype and demonstrate your application with the programs under this license after you have deployed the application for any internal data processing, commercial or production purposes" (Read the full license agreement here) If you want to take advantage of this licensing change and start developing Java EE applications with the #1 Application Server in the world, read now the previous post, How To Install WebLogic Zip on Linux!

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• It could be worse....

  - by Darryl Gove

  As "guest" pointed out, in my file I/O test I didn't open the file with O_SYNC, so in fact the time was spent in OS code rather than in disk I/O. It's a straightforward change to add O_SYNC to the open() call, but it's also useful to reduce the iteration count - since the cost per write is much higher: ... #define SIZE 1024 void test_write() { starttime(); int file = open("./test.dat",O_WRONLY|O_CREAT|O_SYNC,S_IWGRP|S_IWOTH|S_IWUSR); ... Running this gave the following results: Time per iteration 0.000065606310 MB/s Time per iteration 2.709711563906 MB/s Time per iteration 0.178590114758 MB/s Yup, disk I/O is way slower than the original I/O calls. However, it's not a very fair comparison since disks get written in large blocks of data and we're deliberately sending a single byte. A fairer result would be to look at the I/O operations per second; which is about 65 - pretty much what I'd expect for this system. It's also interesting to examine at the profiles for the two cases. When the write() was trapping into the OS the profile indicated that all the time was being spent in system. When the data was being written to disk, the time got attributed to sleep. This gives us an indication how to interpret profiles from apps doing I/O. It's the sleep time that indicates disk activity.

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• Today is my first day in the land of backbone.js

  - by Andrew Siemer - www.andrewsiemer.com

  I am semi-excited to say that today is my first day into the land of backbone.js.  This will of course take me into many other new javascript-y areas.  As I have primarily been focused on building backend systems for the past many years…with no focus on client side bits…this will be all new ground for me.  Very exciting! I am sure that this endeavor will lead to writing about many new findings along the way.  Expect the subject of near future postings to not be related to MVC or server side code. I am starting this journey by reading through the online book “Backbone Fundamentals”.  http://addyosmani.com/blog/backbone-fundamentals/  Has anyone read this yet?  Any feed back on that title. I have read though Derrick Bailey’s thoughts here and here…also very good. Any suggestions on other nuggets of learning backbone?

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• Windows 8: SL and HTML

  - by xamlnotes

  I  was just pointed to comment on my friend Andrew Brust’s blog about Silverlight versus HTML 5. Andrews blog is here: http://geekswithblogs.net/andrewbrust/archive/2011/11/23/windows-8-will-be-here-tomorrow-but-should-silverlight-be.aspx#600915 You can get another idea from another friend of mine Billy Hollis here: http://geekswithblogs.net/jalexander/archive/2011/04/09/the-eternal-battle-rich-v.-reachhellip--guest-blogger-billy-hollis.aspx The commenter is raving about HTML 5 and how that’s the future and SL is not. Well, my reaction is “hogwash”. Sure, HTML 5 is important and does some interesting stuff. Checkout what Bing.com is doing with it on some days and you can see. But to say that XAML is dead is nuts. I have been wrapping up bugs on a cross browser version of an application for awhile now. Whats the state of cross browser today? Well, better than a few years ago but far from perfect.  Each browser vendor interprets the specs in a little different way and you must account for them. The worst offender for major browsers? Apple and its Safari.  I had to make more changes for it than any other. Whats that got to do with XAML and SL/WPF?  Well, you write your SL code once and it runs in all browsers that support it, no changes. ipad does not? Well, they should be taken to court and forced too just like MS and others have been in the past for locking out competitors. Line of business applications? Write them in SL or WPF or both.  Use the power of XAML witch far out reaches html in any flavor and move on. We do need HTML 5 but its not a panacea nor will it replace all other technologies.

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• Where to put business logic in MVC design?

  - by BriskLabs Pakistan

  I have created a simple MVC java application that adds records through data forms to a database. my app collects data, it also validates it and stores it. This is because the data is being sourced online from different users. the data is mostly numeric in nature. now on the numeric data being stored into database (SQL server) , i wish that my app should be able to perform computations... and display it. the user is not interested in how computations are done so they must be encapsulated. the user must only be able to view the simple computed data which for example A column data - B Column data / C column data etc... and just display it to the user... i know how to write stored procedures for same but i want a 3 tier app I want the data, that I put into the database as a record, worked upon by performing calculations on it. However, the original data should remain unaffected, while the new data, post-calculations, must be stored as a new entity record into the database. Where should I write the code for this background calculation? As it is the rules and business logic... in a new java beans files ?

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