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• Clarification of atomic memory access for different OSs

  - by murrekatt

  I'm currently porting a Windows C++ library to MacOS as a hobby project as a learning experience. I stumbled across some code using the Win Interlocked* functions and thus I've been trying to read up on the subject in general. Reading related questions here in SO, I understand there are different ways to do these operations depending on the OS. Interlocked* in Windows, OSAtomic* in MacOS and I also found that compilers have builtin (intrinsic) operations for this. After reading gcc builtin atomic memory access, I'm left wondering what is the difference between intrinsic and the OSAtomic* or Interlocked* ones? I mean, can I not choose between OSAtomic* or gcc builtin if I'm on MacOS when I use gcc? The same if I'd be on Windows using gcc. I also read that on Windows Interlocked* come as both inline and intrinsic versions. What to consider when choosing between intrinsic or inline? In general, are there multiple options on OSs what to use? Or is this again "it depends"? If so, what does it depend on? Thanks!

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• greasemonkey: perform GM_xmlhttpRequest() from eval (follow up)

  - by Paul Tarjan

  How can you call GM_xmlhttpRequest inside of an eval where you are evaling some complicated code, some of which calls GM_xmlhttpRequest. This is a follow up to http://stackoverflow.com/questions/1074236 Here is some sample code: // ==UserScript== // @name Test GM AJAX // ==/UserScript== console = unsafeWindow.console; function fetch(msg) { console.log('fetching: '+msg); GM_xmlhttpRequest({ method: 'GET', url: 'http://google.com', onload: function(responseDetails) { console.log(msg); } }); } function complicated(arg1, arg2) { fetch(arg1 + arg2); } console.log('trying'); var code = 'complicated("Ya", "y!")'; function myEval(code) { eval(code); eval('setTimeout(function(){'+code+'},0)'); eval('setTimeout(fetch,0)'); eval('setTimeout(function(){console.log("here");fetch("cool")},0)'); fetch("BOO"); } myEval(code); which outputs: trying fetching: Yay! fetching: BOO fetching: Yay! fetching: 30 here fetching: cool BOO 30 So the only fetch that worked was the setTimeout(fetch,0) but I need to actually execute the code which includes come complicated code. Any ideas?

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• Entity Framework 5 Enum Naming

  - by Tyrel Van Niekerk

  I am using EF 5 with migrations and code first. It all works rather nicely, but there are some issues/questions I would like to resolve. Let's start with a simple example. Lets say I have a User table and a user type table. The user type table is an enum/lookup table in my app. So the user table has a UserTypeId column and a foreign key ref etc to UserType. In my poco, I have a property called UserType which has the enum type. To add the initial values to the UserType table (or add/change values later) and to create the table in the initial migrator etc. I need a UserType table poco to represent the actual table in the database and to use in the map files. I mapped the UserType property in the User poco to UserTypeId in the UserType poco. So now I have a poco for code first/migrations/context mapping etc and I have an enum. Can't have the same name for both, so do I have a poco called UserType and something else for the enum or have the poco for UserType be UserTypeTable or something? More importantly however, am I missing some key element in how code first works? I tried the example above, ran Add-Migration and it does not add the lookup table for the enum.

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• How can i iterate through QListWidget items and work with each item?

  - by Hossein

  In CSharp its as simple as writting : listBox1.Items.Add("Hello"); listBox1.Items.Add("There"); foreach (string item in listBox1.Items ) { MessageBox.Show(item.ToString()); } and i can easily add different objects to a list box and then retrieve them using foreach. I tried the same approach in Qt 4.8.2 but it seems they are different.though they look very similar at first.I found that Qt supports foreach so i went on and tried something like : foreach(QListWidgetItem& item,ui->listWidget->items()) { item.setTextColor(QColor::blue()); } which failed clearly.It says the items() needs a parameter which confuses me.I am trying to iterate through the ListBox itself, so what does this mean? I tried passing the ListBox object as the parameter itself this again failed too: foreach(QListWidgetItem& item,ui->listWidget->items(ui->listWidget)) { item.setTextColor(QColor::blue()); } So here are my questions: How can I iterate through a QListWidget items in Qt? Can i store objects as items in QListWidgets like C#? How can i convert an object in QListWidgets to string(C#s ToString counter part in Qt) ? (suppose i want to use a QMessagBox instead of that setTextColor and want to print out all string items in the QlistWidget.)

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• What are the lengths/limits C preprocessor as a language creation tool? Where can I learn more about

  - by Weston C

  In his FAQ @ http://www2.research.att.com/~bs/bs_faq.html#bootstrapping, Bjarne Stroustrup says: To build [Cfront, the first C++ compiler], I first used C to write a "C with Classes"-to-C preprocessor. "C with Classes" was a C dialect that became the immediate ancestor to C++... I then wrote the first version of Cfront in "C with Classes". When I read this, it piqued my interest in the C preprocessor. I'd seen its macro capabilities as suitable for simplifying common expressions but hadn't thought about its ability to significantly add to syntax and semantics on the level that I imagine bringing classes to C took. So now I have a couple of questions on my mind: 1) Are there other examples of this approach to bootstrapping a language off of C? 2) Is the source to Stroustrup's original work available anywhere? 3) Where could I learn more about the specifics of utilizing this technique? 4) What are the lengths/limits of that approach? Could one, say, create a set of preprocessor macros that let someone write in something significantly Lisp/Scheme like?

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• Start developing a database application using Oracle + Net Beans

  - by Ranhiru

  I have thought of creating my first database application for one of my projects using Oracle and Java. I have chosen Netbeans as my development environment. I have a few questions to getting started. Please bare with me as I'm a complete beginner to Oracle + Netbeans This will be a data intensive (yet still for a college project) database application. I do not need 1000 user concurrency or any other very advanced features but basic stuff such as triggers, stored procedures etc. Will the 11g "Express" (XE) suffice for my requirements? Do i need any Java to Oracle bridge (database connectivity driver eg. ODBC etc) for Netbeans to connect to the oracle database? If yes, what are they? Does Netbeans support Oracle databases natively? Any easy to follow guide on how do i connect to the database and insert/retrieve/display data on a J2SE application? (I know that i should Google this but if there's any guide previously followed by anyone and is considered easy, it would be greatly appreciated.)

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• Java ternary operator and boxing Integer/int?

  - by Markus

  I tripped across a really strange NullPointerException the other day caused by an unexpected type-cast in the ternary operator. Given this (useless exemplary) function: Integer getNumber() { return null; } I was expecting the following two code segments to be exactly identical after compilation: Integer number; if (condition) { number = getNumber(); } else { number = 0; } vs. Integer number = (condition) ? getNumber() : 0; . Turns out, if condition is true, the if-statement works fine, while the ternary opration in the second code segment throws a NullPointerException. It seems as though the ternary operation has decided to type-cast both choices to int before auto-boxing the result back into an Integer!?! In fact, if I explicitly cast the 0 to Integer, the exception goes away. In other words: Integer number = (condition) ? getNumber() : 0; is not the same as: Integer number = (condition) ? getNumber() : (Integer) 0; . So, it seems that there is a byte-code difference between the ternary operator and an equivalent if-else-statement (something I didn't expect). Which raises three questions: Why is there a difference? Is this a bug in the ternary implementation or is there a reason for the type cast? Given there is a difference, is the ternary operation more or less performant than an equivalent if-statement (I know, the difference can't be huge, but still)?

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• Safari Web Inspector is not updating when I update an element with ajax

  - by Ashley

  I have a checkout page http://www.oipolloi.com/oipolloi/shop/viewbasket.php with multiple ajax calls after certain items update (EG look up postage cost when country is changed, then update discount boxes etc). I've asked for help in the past about the best method of making sure ALL calls have returned before allowing the form to be submitted for payment processing: http://stackoverflow.com/questions/2290372/how-do-i-prevent-form-submission-until-multiple-ajax-calls-have-finished-jquery I was fairly happy that the logic in the finished solution was correct, but I have still been receiving reports that people using Safari are able to submit the form without the ajax calls returning properly. I have tried using the Safari Web Inspector to debug but it seems that when you Inspect Element, then update an element with an ajax call, the Inspector doesn't seem to update. I am updating hidden fields, so it's hard to be able to know whether the problem lies with the DOM not being updated properly, or the Inspector itself. I'm using Safari 4.0.5 on PC and you can reproduce the problem above by looking for a div id="countryFieldsBilling" with Web Inspector. It should contain three hidden fields that are initially empty. You can try to make it update (or not) by choosing a country from the select menu at the bottom of 'Shipping Address' box, and then clicking the 'click to use Shipping Address' link at the top of the 'Billing Address' just below. The behaviour I am seeing is that the country chosen in the shipping select gets copied correctly to the country in the billing select, but the hidden inputs in the Web Inspector do not get updated. When these hidden inputs do not get updated, this causes the problem that Mac Safari users report. If you can let me know either how to get Web Inspector to work properly, or something else I may have missed in the behaviour of Mac Safari that may cause these problems, that would be great. Thanks in advance

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• Understanding how software testing works and what to test.

  - by RHaguiuda

  Intro: I've seen lots of topics here on SO about software testing and other terms I don't understand. Problem: As a beginner developer I, unfortunately, have no idea how software testing works, not even how to test a simple function. This is a shame, but thats the truth. I also hope this question can help others beginners developers too. Question: Can you help me to understand this subject a little bit more? Maybe some questions to start would help: When I develop a function, how should I test it? For example: when working with a sum function, should I test every input value possible or just some limits? How about testing functions with strings as parameters? In a big program, do I have to test every single piece of code of it? When you guys program do you test every code written? How automated test works and how can I try one? How tools for automated testing works and what they do? I`ve heard about unit testing. Can I have a brief explanation on this? What is a testing framework? If possible please post some code with examples to clarify the ideas. Any help on this topic is very welcome! Thanks.

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• Windows 7 versus Windows XP multithreading - Delphi app not acting right

  - by Robert Oschler

  I'm having a problem with a Delphi Pro 6 application that I wrote on my Windows XP machine when it runs on Windows 7. I don't have Windows 7 to test yet and I'm trying to see if Windows 7 might be the source of the trouble. Is there a fundamental difference between the way Windows 7 handles threads compared to Windows XP? I am seeing things happen out of sequence in my error logs on Windows 7 and it's causing problems. For example, objects that should have been initialized are uninitialized when running on Windows 7, yet those objects are initialized on Windows XP by the time they are needed. Some questions: 1) Are there any core differences that could cause threads/processes to behave differently between the two operating system versions? 2) I know this next question may seem absurd, but does Windows 7 attempt to split/fork threads that aren't split/forked on Windows XP? 3) And lastly, are there any known issues with FPU handling that can cause XP programs trouble when run on Windows 7 due to operational differences in wait state handling or register storage, or perhaps something like Exception mask settings, etc? 4) Any 32-bit versus 64-bit issues that could be creating trouble here? -- roschler

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• Rename files and directories using substitution and variables

  - by rednectar

  I have found several similar questions that have solutions, except they don't involve variables. I have a particular pattern in a tree of files and directories - the pattern is the word TEMPLATE. I want a script file to rename all of the files and directories by replacing the word TEMPLATE with some other name that is contained in the variable ${newName} If I knew that the value of ${newName} was say "Fred lives here", then the command find . -name '*TEMPLATE*' -exec bash -c 'mv "$0" "${0/TEMPLATE/Fred lives here}"' {} \; will do the job However, if my script is: newName="Fred lives here" find . -name '*TEMPLATE*' -exec bash -c 'mv "$0" "${0/TEMPLATE/${newName}}"' {} \; then the word TEMPLATE is replaced by null rather than "Fred lives here" I need the "" around $0 because there are spaces in the path name, so I can't do something like: find . -name '*TEMPLATE*' -exec bash -c 'mv "$0" "${0/TEMPLATE/"${newName}"}"' {} \; Can anyone help me get this script to work so that all files and directories that contain the word TEMPLATE have TEMPLATE replaced by whatever the value of ${newName} is eg, if newName="A different name" and a I had directory of /foo/bar/some TEMPLATE directory/with files then the directory would be renamed to /foo/bar/some A different name directory/with files and a file called some TEMPLATE file would be renamed to some A different name file

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• Really Need a Facebook App to post to Facebook Page Wall?

  - by Lee Englestone

  Hi, I'm using the Facebook API Graph (C# & ASP.NET) to try to dynamically post to a Facebook page I created. Looking at the code samples floating around.. they suggest creating a Facebook App first (which I have done).. However.. I have 3 different pages I want to post to.. Do I need to create an app for each? (I want to post different things to the 3 pages, not the same posts to each) I just want messages & links to appear as Wall posts. I'm not bothered about having an 'app' that has 'canvas' that is placed in an IFrame. Question : So do I still need to write one or more Facebook Apps to post to my 3 different Facebook pages?? Where I am so far.. I can pass in my apps credentials and get back the access_token. But my posts don't appear to be going anywhere. I'd rather drop the 'facebook application /canvas' approach if possible If I can post directly to a wall (For the above reasons). Oh, and before you ask. I don't want to post to my Apps Wall page, I want to post to my other pages (Unless I have to post to my Apps Wall page first?). I'm sure loads of people have the same questions.. Thanks in advance. -- Lee

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• problem configure JBoss to work with JNDI(2)

  - by Spiderman

  in continuation to the question from last week: http://stackoverflow.com/questions/2828237/problem-configure-jboss-to-work-with-jndi I'm trying to bind datasource in JBoss and use it in my application. In my struggling, I already managed to avoid the javax.naming.NameNotFoundException by: 1. using in java new InitialContext().lookup(connection); instead of new JndiObjectFactoryBean().setJndiName(connection); 2. changing the connection name from: 'jndi-name' to 'java:jndi-name' Now the problem is that the datasouce that I get from the lookup is null. I created the datsource file: <datasources> <local-tx-datasource> <jndi-name>bilby</jndi-name> <connection-url>jdbc:oracle:myURL</connection-url> <driver-class>oracle.jdbc.OracleDriver </driver-class> <user-name>myUsername</user-name> <password>myPassword</password> <exception-sorter-class- name>org.jboss.resource.adapter.jdbc.vendor.OracleExceptionSorter</exception-sorter-class-name> <metadata> <type-mapping>Oracle9i</type-mapping> </metadata> </local-tx-datasource> </datasources> and put it under \server\default\deploy\oracle-ds.xml I get during runtime the line: 18:37:56,560 INFO [ConnectionFactoryBindingService] Bound ConnectionManager 'jb oss.jca:service=DataSourceBinding,name=bilby' to JNDI name 'java:bilby' So my question is - why do I get null as my datasource???

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• Is XSLT worth investing time in and are there any actual alternatives?

  - by Keeno

  I realize this has been a few other questions on this topic, and people are saying use your language of choice to manipulate the XML etc etc however, not quite fit my question exactly. Firstly, the scope of the project: We want to develop platform independent e-learning, currently, its a bunch of HTML pages but as they grow and develop they become hard to maintain. The idea: Generate up an XML file + Schema, then produce some XSLT files that process the XML into the eLearning modiles. XML to HTML via XSLT. Why: We would like the flexibilty to be able to easy reformat the content (I realize CSS is a viable alternative here) If we decide to alter the pages layout or functionality in anyway, im guessing altering the "shared" XSLT files would be easier than updating the HTML files. So far, we have about 30 modules, with up to 10-30 pages each Depending on some "parameters" we could output drastically different page layouts/structures, above and beyond what CSS can do Now, all this has to be platform independent, and to be able to run "offline" i.e. without a server powering the HTML Negatives I've read so far for XSLT: Overhead? Not exactly sure why...is it the compute power need to convert to HTML? Difficult to learn Better alternatives Now, what I would like to know exactly is: are there actually any viable alternatives for this "offline"? Am I going about it in the correct manner, do you guys have any advice or alternatives. Thanks!

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• Pushing a local mercurial repository to a remote server or cloning at server from local

  - by Samaursa

  I have a local repository that I have now decided to push to a remote server (for example, I have a host that allows mercurial repositories and I am also trying to push to bitbucket). The repository has a lot of files and is a little more than 200mb. Locally, I am able to clone the repository without problems. Now I have a lot of changes in this repository, and I have wasted a couple of days trying to figure out how to get the remote server to clone my repository. I cannot get hg serve to work outside of the LAN. I have tried everything. So instead, I created a new repository at the remote servers (both at the host and bitbucket) with nothing in it. Now I am pushing the complete repository that I have locally to these remote locations. So far it has been unsuccessful, as the push operation is stuck on searching for changes and does not give me any other useful output. I have let it go for about an hour with no change. Now my questions is, what am I doing wrong as far as hg serve is concerned? I can access it locally but not remotely (through DynDns - I have configured it properly and the router forwards the ports correctly) so that I can get the server to clone the repository the first time after which I will be pushing to it. My second question is, assuming the clone at server does not work (for example, if I was to push my current repository to bitbucket), is creating an empty repository at the server and then pushing a local repository to the new remote repository ok? Is that the source of the searching for changes problem? Any help in this regard would be greatly appreciated.

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• Jquery Sorting by Letter

  - by Batfan

  I am using jquery to sort through a group of paragraph tags (kudos to Aaron Harun). It pulls the value "letter" (a letter) from the url string and displays only paragraphs that start with that letter. It hides all others and also consolidates the list so that there are no duplicates showing. See the code: var letter = '<?php echo(strlen($_GET['letter']) == 1) ? $_GET['letter'] : ''; ?>' function finish(){ var found_first = []; jQuery('p').each(function(){ if(jQuery(this).text().substr(0,1).toUpperCase() == letter){ if(found_first[jQuery(this).text()] != true){ jQuery(this).addClass('current-series'); found_first[jQuery(this).text()] = true; }else{ jQuery(this).hide(); } } else{ jQuery(this).hide();} }) } Been working with this all day and I have 2 Questions on this: Is there a way to get it to ignore the word 'The', if it's first? For example, if a paragraph starts with 'The Amazing', I would like it to show up on the 'A' page, not the 'T' page, like it currently is. Is there a way to have a single page for (all) numbers? For example, the url to the page would be something similar to domain.com/index.php?letter=0 and this would show only the paragraph tags that start with a number, any number. I can currently do this with single numbers but, I would like 1 page for all numbers.

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• django-cms lighttpd redirect domain to url

  - by Robert

  Hello, I am using djano-cms for my site, but instead of language alias /en/ /de/ I need to use another domain. I would like to avoid running multiple django instances, and instead I would like to use lighttpd redirects if possible. I would like requests coming to domain2.com getting data from domain.com/en . The best would be if the user entering: domain2.com/offer got transparently data from domain.com/en/offer Tried many solutions with url.redirect, url.rewrite but none seems to work as desired. Also tried with: http://stackoverflow.com/questions/261904/matching-domains-with-regex-for-lighttpd-mod-evhost-www-domain-com-domain-com but that didn't work. Please help. This is my lighttpd configuration. $HTTP["host"] == "^domain2\.com" { url.redirect = ("^/(.*)" => "http://domain.com/en/$1") } $HTTP["host"] =~ "^domain\.com" { server.document-root = "/var/www/django/projects/domain/" accesslog.filename = "/var/log/lighttpd/domain.log-access.log" server.errorlog = "/var/log/lighttpd/www.domain-error.log" fastcgi.server = ( "/domain-service.fcgi" => ( "main" => ( "socket" => "/tmp/django-domain.sock", "check-local" => "disable", ) ), ) alias.url = ( "/media/" => "/var/www/django/projects/domain/media/", ) url.rewrite-once = ( "^(/site_media.*)$" => "$1", "^(/media.*)$" => "$1", "^/favicon\.ico$" => "/media/favicon.ico", "^(/.*)$" => "/domain-service.fcgi$1", } Thanks

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• I can learn either C or Java, which one should I choose first? Should I take them concurrently?

  - by GR1000

  I realize this is a subject of hot debate, but I'm interested in opinions that relate to my specific situation. I want to learn the basics and fundamentals of programming, so I'm already taking a college course in general programming concepts. It isn't covering a specific language, but it's giving me a solid foundation that I can build upon when I move on to a class that teaches a specific language. My two options for a specific language are Java and C because those are the two languages taught at the college I want to take classes from. What I want to do is learn a complex language so that I can apply that knowledge to languages that I use, or will eventually use, in my current job building web pages: XHTML, CSS, JavaScript, PHP, XML, ActionScript. I'm not necessariy interested in becoming a Java developer or a C developer in the immediate future, but I do have aspirations of developing web applications and iPod/iPhone applications. So, basically, I'm looking for answers to these questions and the reasoning behind them: Do I take the introductory course in Java first, and then take the intro course in C, or Do I take C first and then take Java? Is there any reason not to take them concurrently? Should I skip C altogether as Java covers everything I need to know? EDIT: Thanks everyone for your thoughtful and insightful responses.

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• Calling delegate methods and calling selectors

  - by Crystal

  I'm new to the concept of delegates and selectors when used with notifications. So my first question is, 1) Let's say you have a button that has a delegate that implements some doWork method. If you want the same functionality that's in the method, is it 'ok' to just call that method? I didn't know if that was considered good coding practices and/or if you should do that, or do something different in getting that type of functionality. Like if that is ok architecture? 2) Similarly, with NSNotificationCenter, I see some code that posts a notification. Then there's a HandleSegmentedControl:(NSNotification *)notification method. If I want to manually have that functionality, but without pressing the segment control, is it 'ok' to just take that functionality out of that method and put it in a new method so it would look like this: Original: - (void)HandleSegmentedControl:(NSNotification *)notification { NSDictionary *dict = [userInfo notification]; // do stuff with the dictionary } New: - (void)HandleSegmentedControl:(NSNotification *)notification { NSDictionary *dict = [userInfo notification]; [self newMethod:dict]; } - (void)newMethod:(NSDictionary *)dict { // do stuff with the dictionary } - (void)myOtherMethodThatNeedsTheSameFunctionality { NSDictionary *dict = // create some dictionary [self newMethod:dict]; } Sorry if these are basic questions. I'm not sure what the best practices are for things like this and wanted to start the right way. Thanks.

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• Python: Serial Transmission

  - by Silent Elektron

  I have an image stack of 500 images (jpeg) of 640x480. I intend to make 500 pixels (1st pixels of all images) as a list and then send that via COM1 to FPGA where I do my further processing. I have a couple of questions here: How do I import all the 500 images at a time into python and how do i store it? How do I send the 500 pixel list via COM1 to FPGA? I tried the following: Converted the jpeg image to intensity values (each pixel is denoted by a number between 0 and 255) in MATLAB, saved the intensity values in a text file, read that file using readlines(). But it became too cumbersome to make the intensity value files for all the 500 images! Used NumPy to put the read files in a matrix and then pick the first pixel of all images. But when I send it, its coming like: [56, 61, 78, ... ,71, 91]. Is there a way to eliminate the [ ] and , while sending the data serially? Thanks in Advance! :)

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• XForms relation of 'constraint' and 'required' properties

  - by Danny

  As a reference, the most similar question already asked is: http://stackoverflow.com/questions/8667849/making-xforms-enforce-the-constraint-and-type-model-item-properties-only-when-fi The difference is that I cannot use the relevant properties since I do want the field to be visible and accessible. I'm attempting to make a XForms form that has the following properties: It displays a text field named 'information'. (for the example) This field must not be required, since it may not be necessary to enter data. (Or this data will be entered at a later time.) However, if data is entered in this field, it must adhere to the specified constraint. I cannot mark the field as not relevant since this would hide the field and some data may need to be entered in it. The trouble now is that even though the field has no data in it, the constraint is still enforced (i.e. even though it is not marked as 'required'). I have taken a look at the XForms 1.1 specification, however it does not seem to describe how the properties 'required' and 'constraint' should interact. The only option I see, is to add a part to the constraint such that an empty value is allowed. e.g.: . = '' or <actual-constraint However, I don't like this. It feels like a workaround to add this to every such field. Is there any other way to express that non-required fields should not need to match the constraint for that field? (Am I missing something?)

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• Still Confused About Identifying vs. Non-Identifying Relationships

  - by Jason

  So, I've been reading up on identifying vs. non-identifying relationships in my database design, and a number of the answers on SO seem contradicting to me. Here are the two questions I am looking at: What's the Difference Between Identifying and Non-Identifying Relationships Trouble Deciding on Identifying or Non-Identifying Relationship Looking at the top answers from each question, I appear to get two different ideas of what an identifying relationship is. The first question's response says that an identifying relationship "describes a situation in which the existence of a row in the child table depends on a row in the parent table." An example of this that is given is, "An author can write many books (1-to-n relationship), but a book cannot exist without an author." That makes sense to me. However, when I read the response to question two, I get confused as it says, "if a child identifies its parent, it is an identifying relationship." The answer then goes on to give examples such as SSN (is identifying of a Person), but an address is not (because many people can live at an address). To me, this sounds more like a case of the decision between primary key and non-primary key. My own gut feeling (and additional research on other sites) points to the first question and its response being correct. However, I wanted to verify before I continued forward as I don't want to learn something wrong as I am working to understand database design. Thanks in advance.

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• Typical Hadoop setup for remote job submission

  - by Artii

  So I am still a bit new to hadoop and am currently in the process of setting up a small test cluster on Amazonaws. So my question relates to some tips on the structuring of the cluster so it is possible to work submit jobs from remote machines. Currently I have 5 machines. 4 are basically the Hadoop cluster with the NameNodes, Yarn etc. One machine is used as a manager machine( Cloudera Manager). I am gonna describe my thinking process on the setup and if anyone can chime in the points I am not clear with, that would be great. I was thinking what was the best setup for a small cluster. So I decided to expose only one manager machine and probably use that to submit all the jobs through it. The other machines will see each other etc, but not be accessible from the outside world. I am have conceptual idea on how to do this,but I am not sure how to properly go about doing this though, if anyone could point me in the right direction that would great. Also another big point is, I want to be able to submit jobs to the cluster through exposed machine from a client machine (might be Windows). I am not so clear on this setup as well. Do I need to have Hadoop installed on the machine in order to use the normal hadoop commands, and to write/submit jobs say from Eclipse or something similar. So to sum it up my questions are, Is this an ok setup for a small test cluster How can I go about using one exposed machine to submit/route jobs to the cluster, without having any of the Hadoop nodes on it. How do I setup a client machine to submit jobs to a remote cluster, and an example on how to do it on Windows. Also if there are any reason not to use Windows as a client machine in this setup. Thanks I would greatly appreciate any advice or help on this.

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• Searching in graphs trees with Depth/Breadth first/A* algorithms

  - by devoured elysium

  I have a couple of questions about searching in graphs/trees: Let's assume I have an empty chess board and I want to move a pawn around from point A to B. A. When using depth first search or breadth first search must we use open and closed lists ? This is, a list that has all the elements to check, and other with all other elements that were already checked? Is it even possible to do it without having those lists? What about A*, does it need it? B. When using lists, after having found a solution, how can you get the sequence of states from A to B? I assume when you have items in the open and closed list, instead of just having the (x, y) states, you have an "extended state" formed with (x, y, parent_of_this_node) ? C. State A has 4 possible moves (right, left, up, down). If I do as first move left, should I let it in the next state come back to the original state? This, is, do the "right" move? If not, must I transverse the search tree every time to check which states I've been to? D. When I see a state in the tree where I've already been, should I just ignore it, as I know it's a dead end? I guess to do this I'd have to always keep the list of visited states, right? E. Is there any difference between search trees and graphs? Are they just different ways to look at the same thing?

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• Haskell Cons Operator (:)

  - by Carson Myers

  I am really new to Haskell (Actually I saw "Real World Haskell" from O'Reilly and thought "hmm, I think I'll learn functional programming" yesterday) and I am wondering: I can use the construct operator to add an item to the beginning of a list: 1 : [2,3] [1,2,3] I tried making an example data type I found in the book and then playing with it: --in a file data BillingInfo = CreditCard Int String String | CashOnDelivery | Invoice Int deriving (Show) --in ghci $ let order_list = [Invoice 2345] $ order_list [Invoice 2345] $ let order_list = CashOnDelivery : order_list $ order_list [CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, CashOnDelivery, ...- etc... it just repeats forever, is this because it uses lazy evaluation? -- EDIT -- okay, so it is being pounded into my head that let order_list = CashOnDelivery:order_list doesn't add CashOnDelivery to the original order_list and then set the result to order_list, but instead is recursive and creates an infinite list, forever adding CashOnDelivery to the beginning of itself. Of course now I remember that Haskell is a functional language and I can't change the value of the original order_list, so what should I do for a simple "tack this on to the end (or beginning, whatever) of this list?" Make a function which takes a list and BillingInfo as arguments, and then return a list? -- EDIT 2 -- well, based on all the answers I'm getting and the lack of being able to pass an object by reference and mutate variables (such as I'm used to)... I think that I have just asked this question prematurely and that I really need to delve further into the functional paradigm before I can expect to really understand the answers to my questions... I guess what i was looking for was how to write a function or something, taking a list and an item, and returning a list under the same name so the function could be called more than once, without changing the name every time (as if it was actually a program which would add actual orders to an order list, and the user wouldn't have to think of a new name for the list each time, but rather append an item to the same list).

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