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  • substitute in a nested list (prolog)

    - by linda
    /* substitute(X,Y,Xs,Ys) is true if the list Ys is the result of substituting Y for all occurrences of X in the list Xs. This is what I have so far: subs(_,_,[],[]). subs(X,Y,[X|L1],[Y|L2]):- subs(X,Y,L1,L2). subs(X,Y,[H|L1],[H|L2]):- X\=H, not(H=[_|_]), subs(X,Y,L1,L2). subs(X,Y,[H|_],[L2]):- X\=H, H=[_|_], subs(X,Y,H,L2). My code works except it omits the elements following the nested list. For example: ?- subs(a,b,[a,[a,c],a],Z). Z = [b, [b, c]] . What should I add to this program?

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  • SharePoint The My Site of <user name> is scheduled for deletion.

    - by Linda
    Hi there, In my email today I got the following: The My Site of is scheduled for deletion. As their manager you are now the temporary owner of their site. This temporary ownership gives you access to the site to copy any business-related information you might need. To access the site use this URL: http://mysites.freud.com/personal/ I click on the link and I can see that there site is there. I do not want there site to be deleted at all what can I do. When I search for the user using the PeopleSearchBoxEx web part the user comes up but when I click on there name I get the error: Server Error in '/' Application. -------------------------------------------------------------------------------- User not found. Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code. Exception Details: Microsoft.SharePoint.SPException: User not found. Source Error: An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. Stack Trace: [SPException: User not found.] Microsoft.SharePoint.Portal.WebControls.ProfilePropertyLoader.OnInit(EventArgs e) +4415 System.Web.UI.Control.InitRecursive(Control namingContainer) +333 System.Web.UI.Control.InitRecursive(Control namingContainer) +210 System.Web.UI.Control.InitRecursive(Control namingContainer) +210 System.Web.UI.Control.InitRecursive(Control namingContainer) +210 System.Web.UI.Control.InitRecursive(Control namingContainer) +210 System.Web.UI.Control.InitRecursive(Control namingContainer) +210 System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +378 Any idea how I can stop this person from being "delete" and get there profile to work again?

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  • Drupal ical for Authenticated users

    - by Linda
    I am using the calender module with it's iCal support for Drupal 6. I have made my event type which appear on the iCal feed. I however want to make the event content type private, so only authenticated users can read it. By doing this they will not show on the iCal feed. Is there any way that I could get the iCal feed to still show these events?

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  • PHP output results on to one page

    - by linda
    i have a system where a user searches for a film and reviews appear on a page with a button next to each review. The button can be selected to look at the individual review but i basically want a button that when selected it will look at all reviews on one page, the code i am using for the individual review is this <?php ini_set ('display_errors', 1); error_reporting (E_ALL & ~E_NOTICE); $searchfilm=$_POST['searchfilm']; //Connect to database //Filter search $searchfilm = strtoupper($searchfilm); $searchfilm = strip_tags($searchfilm); $searchfilm = trim ($searchfilm); $query = mysql_fetch_assoc(mysql_query("SELECT filmreview FROM review WHERE id = '$id'")); $data = mysql_query("SELECT film.filmname, review.filmreview, review.reviewtitle, review.id FROM film, review WHERE film.filmid = review.filmid AND filmname = '$searchfilm'"); while($row = mysql_fetch_assoc($data)) { // echo $row['filmname']; // echo "<b>Film Name:</b> " .$searchfilm; echo "<table border=\"2\" align=\"left\">"; echo "<tr><td>"; echo "<b>Review Title:</b> " .$row['reviewtitle']; echo "<tr><td>"; echo $row['filmreview']; echo "<p>"; echo "<form method='post' action='analyse1.php'>"; echo "<input type='hidden' name='reviewid' value='".$row['id']."'>"; echo "<input type='submit' name='submit' value='Analyse'>"; echo "</form>"; echo "</table>"; } ?>

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  • Submtting data using $.ajax and retrieving values from $_POST array

    - by Linda Keating
    I'm having trouble retrieving my form Data that has been submitted via ajax like this: $( "form" ).on( "submit", function( event ) { var formData = $(this).serializeArray(); console.log("fomData"); $.ajax({ url: window.location.origin+ "/selfservicemanager/localtmfsetup/local_tmf_setup.php", type: "POST", data: JSON.stringify(formData), success : function (){ alert("success"); } }); }); I can see the data being sent over the network like this: But when I try to retrieve the data on the server side the $_POST array is empty. <?php var_dump($_POST); die(); ?> array (size=0) empty Any ideas? I've tried to stringify the data being sent, and also tried to decode the $_POST array but it expects a string.....

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  • Bootstrap-Switch options don't take effect

    - by Linda Keating
    I'm using Bootstrap-Switch and the documentation says that options can be passed as an object on initialization. enter link description here And here is a list of options: enter link description here So my code looks like this: var options = { onText: "Yes", onColor: 'primary', offColor: 'danger', offText: "No", animate: true, }; $("[name='radioGroup1']").bootstrapSwitch(options); And it all switch works fine, but none of the defaults are overwritten by the options. Anybody got any examples of how this might work? Thanks

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  • Drupal return number of results in a View

    - by Linda
    I have a view in Drupal that filters my content. It brings back 7 rows. All I want to return is the number or results returned(7). Is this possible? I tried using the View result counter but it returns a number for each results 1 2 3 4 5 6 7 I just need the 7 part. So in SQL I would do a select count(*)

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  • How can I superimpose modified loess lines on a ggplot2 qplot?

    - by briandk
    Background Right now, I'm creating a multiple-predictor linear model and generating diagnostic plots to assess regression assumptions. (It's for a multiple regression analysis stats class that I'm loving at the moment :-) My textbook (Cohen, Cohen, West, and Aiken 2003) recommends plotting each predictor against the residuals to make sure that: The residuals don't systematically covary with the predictor The residuals are homoscedastic with respect to each predictor in the model On point (2), my textbook has this to say: Some statistical packages allow the analyst to plot lowess fit lines at the mean of the residuals (0-line), 1 standard deviation above the mean, and 1 standard deviation below the mean of the residuals....In the present case {their example}, the two lines {mean + 1sd and mean - 1sd} remain roughly parallel to the lowess {0} line, consistent with the interpretation that the variance of the residuals does not change as a function of X. (p. 131) How can I modify loess lines? I know how to generate a scatterplot with a "0-line,": # First, I'll make a simple linear model and get its diagnostic stats library(ggplot2) data(cars) mod <- fortify(lm(speed ~ dist, data = cars)) attach(mod) str(mod) # Now I want to make sure the residuals are homoscedastic qplot (x = dist, y = .resid, data = mod) + geom_smooth(se = FALSE) # "se = FALSE" Removes the standard error bands But does anyone know how I can use ggplot2 and qplot to generate plots where the 0-line, "mean + 1sd" AND "mean - 1sd" lines would be superimposed? Is that a weird/complex question to be asking?

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  • JCP Awards 10 Year Retrospective

    - by Heather VanCura
    As we celebrate 10 years of JCP Program Award recognition in 2012,  take a look back in the Retrospective article covering the history of the JCP awards.  Most recently, the JCP awards were  celebrated at JavaOne Latin America in Brazil, where SouJava was presented the JCP Member of the Year Award for 2012 (won jointly with the London Java Community) for their contributions and launch of the Global Adopt-a-JSR Program. This is also a good time to honor the JCP Award Nominees and Winners who have been designated as Star Spec Leads.  Spec Leads are key to the Java Community Process (JCP) program. Without them, none of the Java Specification Requests (JSRs) would have begun, much less completed and become implemented in shipping products.  Nominations for 2012 Start Spec Leads are now open until 31 December. The Star Spec Lead program recognizes Spec Leads who have repeatedly proven their merit by producing high quality specifications, establishing best practices, and mentoring others. The point of such honor is to endorse the good work that they do, showcase their methods for other Spec Leads to emulate, and motivate other JCP program members and participants to get involved in the JCP program. Ed Burns – A Star Spec Lead for 2009, Ed first got involved with the JCP program when he became co-Spec Lead of JSR 127, JavaServer Faces (JSF), a role he has continued through JSF 1.2 and now JSF 2.0, which is JSR 314. Linda DeMichiel – Linda thus involved in the JCP program from its very early days. She has been the Spec Lead on at least three JSRs and an EC member for another three. She holds a Ph.D. in Computer Science from Stanford University. Gavin King – Nominated as a JCP Outstanding Spec Lead for 2010, for his work with JSR 299. His endorsement said, “He was not only able to work through disputes and objections to the evolving programming model, but he resolved them into solutions that were more technically sound, and which gained support of its pundits.” Mike Milikich –  Nominated for his work on Java Micro Edition (ME) standards, implementations, tools, and Technology Compatibility Kits (TCKs), Mike was a 2009 Star Spec Lead for JSR 271, Mobile Information Device Profile 3. David Nuescheler – Serving as the CTO for Day Software, acquired by Adobe Systems, David has been a key player in the growth of the company’s global content management solution. In 2002, he became Spec Lead for JSR 170, Content Repository for Java Technology API, continuing for the subsequent version, JSR 283. Bill Shannon – A well-respected name in the Java community, Bill came to Oracle from Sun as a Distinguished Engineer and is still performing at full speed as Spec Lead for JSR 342, Java EE 7,  as an alternate EC member, and hands-on problem solver for the Java community as a whole. Jim Van Peursem – Jim holds a PhD in Computer Engineering. He was part of the Motorola team that worked with Sun labs on the Spotless VM that became the KVM. From within Motorola, Jim has been responsible for many aspects of Java technology deployment, from an independent Connected Limited Device Configuration (CLDC) and Mobile Information Device Profile (MIDP) implementations, to handset development, to working with the industry in defining many related standards. Participation in the JCP Program goes well beyond technical proficiency. The JCP Awards Program is an attempt to say “Thank You” to all of the JCP members, Expert Group Members, Spec Leads, and EC members who give their time to contribute to the evolution of Java technology.

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  • Transactional Interceptors in Java EE 7 - Request for feedback

    - by arungupta
    Linda described how EJB's container-managed transactions can be applied to the Java EE 7 platform as a whole using a solution based on CDI interceptors. This can then be used by other Java EE components as well, such as Managed Beans. The plan is to add an annotation and standardized values in the javax.transaction package. For example: @Inherited @InterceptorBinding @Target({TYPE, METHOD}) @Retention(RUNTIME) public @interface Transactional { TxType value() default TxType.REQUIRED } And then this can be specified on a class or a method of a class as: public class ShoppingCart { ... @Transactional public void checkOut() {...} ... } This interceptor will be defined as part of the update to Java Transactions API spec at jta-spec.java.net. The Java EE 7 Expert Group needs your help and looking for feedback on the exact semantics. The complete discussion can be read here. Please post your feedback to [email protected] and we'll also consider comments posted to this entry.

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  • grub rescue: grub not installed

    - by linda8
    I tried to install beside my windows 7. It didn't work. After installing it could not find the root directory and I got some other error messages... I just wanted my computer to be faster again so instead I decided to reinstall windows from recovery disk. It formatted the disk and installed windows again. The hard-disk has msdos structure now and the ubuntu partition is empty When I start up the computer grab is starting up an I get a grab rescue problem, but grab is no longer installed. How can I boot directly into windows? i can boot Ubuntu from an usb stick but I'm not able to install it anymore. I just want windows to work again... I'm hoping for advice... Linda

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  • Efficient method of getting all plist arrays into one array?

    - by cannyboy
    If I have a plist which is structured like this: Root Array Item 0 Dictionary City String New York People Array Item 0 String Steve Item 1 String Paul Item 2 String Fabio Item 3 String David Item 4 String Penny Item 1 Dictionary City String London People Array Item 0 String Linda Item 1 String Rachel Item 2 String Jessica Item 3 String Lou Item 2 Dictionary City String Barcelona People Array Item 0 String Edward Item 1 String Juan Item 2 String Maria Then what is the most efficient way of getting all the names of the people into one big NSArray?

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  • Favorite Programmer Quotes…

    - by SGWellens
      "A computer once beat me at chess, but it was no match for me at kick boxing." — Emo Philips   "There are only 10 types of people in the world, those who understand binary and those who don't. " – Unknown.   "Premature optimization is the root of all evil." — Donald Knuth   "I should have become a doctor; then I could bury my mistakes." — Unknown   "Code softly and carry a large backup thumb drive." — Me   "Always code as if the guy who ends up maintaining your code will be a violent psychopath who knows where you live." — Martin Golding   "DDE…the protocol from hell"— Charles Petzold   "Just because a thing is new don't mean that it's better" — Will Rogers   "The mark of a mature programmer is willingness to throw out code you spent time on when you realize it's pointless." — Bram Cohen   "A good programmer is someone who looks both ways before crossing a one-way street." — Doug Linder   "The early bird may get the worm but it's the second mouse that gets the cheese." — Unknown   I hope someone finds this amusing. Steve Wellens CodeProject

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  • Why isn't DSM for unstructured memory done today?

    - by sinned
    Ages ago, Djikstra invented IPC through mutexes which then somehow led to shared memory (SHM) in multics (which afaik had the necessary mmap first). Then computer networks came up and DSM (distributed SHM) was invented for IPC between computers. So DSM is basically a not prestructured memory region (like a SHM) that magically get's synchronized between computers without the applications programmer taking action. Implementations include Treadmarks (inofficially dead now) and CRL. But then someone thought this is not the right way to do it and invented Linda & tuplespaces. Current implementations include JavaSpaces and GigaSpaces. Here, you have to structure your data into tuples. Other ways to achieve similar effects may be the use of a relational database or a key-value-store like RIAK. Although someone might argue, I don't consider them as DSM since there is no coherent memory region where you can put data structures in as you like but have to structure your data which can be hard if it is continuous and administration like locking can not be done for hard coded parts (=tuples, ...). Why is there no DSM implementation today or am I just unable to find one?

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  • How to use the Response from PHP in Objective-C?

    - by iMohammad
    I've managed to post and get datas from PHP thru objective-c. However, the response from the server looks like the following: ["ARC101","ARC112","ARC124","ARC203","ARC222","ARC251","ARC281","ARC305","ARC314","ARC344","ARC353","ARC363","ARC408","ARC416","ARC426","ARC482"] And, some responses could be more complicated like the following: [{"Code":"ARC101","Title":"Design Studio-I: Design Princi","Instructor":"Mike Cohen","Activity":"LAB","Days":"MW","Room":"B01","Bldg":"19","Section":"1","StartTime":"1310","EndTime":"1550","CallNo":"20438","Priority":null,"Open":"Open","HasAct":false,"CodeAct":null,"TitleAct":null,"InstructorAct":null] What would be your suggestion if I want to play with these datas? for example, putting them on a table ,etc. Thanks in Advance!

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  • array_count_values for javascript instead

    - by user626342
    Hi, I have the following php-script, now I need to do the same thing in javascript. Is there a funcion in javascript that works similar to the php function, I have been searching for days but cannot find anything similar? What I want to do is to count the number of times a certain word is beeing used in an array. $interfaceA = array($interfaceA_1,$interfaceA_2,$interfaceA_3,$interfaceA_4,$interfaceA_5,$interfaceA_6,$interfaceA_7,$interfaceA_8); $interfaceA_array=array_count_values($interfaceA); $knappsatsA = $interfaceA_array[gui_knappsats]; $touchpanelA = $interfaceA_array[gui_touchpanel]; Many thanks linda

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  • JCP.Next - Early Adopters of JCP 2.8

    - by Heather VanCura
    JCP.Next is a series of three JSRs (JSR 348, JSR 355 and JSR 358), to be defined through the JCP process itself, with the JCP Executive Committee serving as the Expert Group. The proposed JSRs will modify the JCP's processes  - the Process Document and Java Specification Participation Agreement (JSPA) and will apply to all new JSRs for all Java platforms.   The first - JCP.next.1, or more formally JSR 348, Towards a new version of the Java Community Process - was completed and put into effect in October 2011 as JCP 2.8. This focused on a small number of simple but important changes to make our process more transparent and to enable broader participation. We're already seeing the benefits of these changes as new and existing JSRs adopt the new requirements. The second - JSR 355, Executive Committee Merge, is also Final. You can read the JCP 2.9 Process Document .  As part of the JSR 355 Final Release, the JCP Executive Committee published revisions to the JCP Process Document (version 2.9) and the EC Standing Rules (version 2.2).  The changes went into effect following the 2012 EC Elections in November. The third JSR 358, A major revision of the Java Community Process was submitted in June 2012.  This JSR will modify the Java Specification Participation Agreement (JSPA) as well as the Process Document, and will tackle a large number of complex issues, many of them postponed from JSR 348. For these reasons, the JCP EC (acting as the Expert Group for this JSR), expects to spend a considerable amount of time working on. The JSPA is defined by the JCP as "a one-year, renewable agreement between the Member and Oracle. The success of the Java community depends upon an open and transparent JCP program.  JSR 358, A major revision of the Java Community Process, is now in process and can be followed on java.net. The following JSRs and Spec Leads were the early adopters of JCP 2.8, who voluntarily migrated their JSRs from JCP 2.x to JCP 2.8 or above.  More candidates for 2012 JCP Star Spec Leads! JSR 236, Concurrency Utilities for Java EE (Anthony Lai/Oracle), migrated April 2012 JSR 308, Annotations on Java Types (Michael Ernst, Alex Buckley/Oracle), migrated September 2012 JSR 335, Lambda Expressions for the Java Programming Language (Brian Goetz/Oracle), migrated October 2012 JSR 337, Java SE 8 Release Contents (Mark Reinhold/Oracle) – EG Formation, migrated September 2012 JSR 338, Java Persistence 2.1 (Linda DeMichiel/Oracle), migrated January 2012 JSR 339, JAX-RS 2.0: The Java API for RESTful Web Services (Santiago Pericas-Geertsen, Marek Potociar/Oracle), migrated July 2012 JSR 340, Java Servlet 3.1 Specification (Shing Wai Chan, Rajiv Mordani/Oracle), migrated August 2012 JSR 341, Expression Language 3.0 (Kin-man Chung/Oracle), migrated August 2012 JSR 343, Java Message Service 2.0 (Nigel Deakin/Oracle), migrated March 2012 JSR 344, JavaServer Faces 2.2 (Ed Burns/Oracle), migrated September 2012 JSR 345, Enterprise JavaBeans 3.2 (Marina Vatkina/Oracle), migrated February 2012 JSR 346, Contexts and Dependency Injection for Java EE 1.1 (Pete Muir/RedHat) – migrated December 2011

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  • Don't Miss At Devoxx!!!

    - by Yolande Poirier
    Come by IoT Hack Fest which starts with the session: kickstart your Raspberry Pi and/or Leap Motion project, part II on Tuesday from 9:30am to 12:00pm to learn how to start a project with the Raspberry Pi and Leap Motion. In the afternoon, you can still join a project and create your own project with the help of experts on Raspberry Pi, Leap Motion and other boards.  At the Oracle booth, Java experts will be available  to answer your  questions and demo the new features of the Java Platform, including Java Embedded, JavaFX, Java SE and Java EE. This year, the chess game that was first demoed at JavaOne keynotes last September will be showcased at Devoxx.  Duke is coming to Devoxx this year. You can get your picture taken with Duke on Tuesday, Wednesday and Thursday (Nov. 12-14) from 12:00 to 18:00 Beer bash will be Tuesday from 17:30-19:30 and Wednesday/Thursday from 18:00 to 20:00 at the booth. Oracle is raffling off five Raspberry Pi's and a number of books every day. Make sure to stop by and get your badge scanned to enter the raffle. Raffles are Tuesday at 19:15 and Wednesday/Thursday at 19:45 at the Oracle booth.  The main conference sessions from Oracle Java experts are:  Wednesday 13 November Beyond Beauty: JavaFX, Parallax, Touch, Raspberry Pi, Gyroscopes, and Much More Angela Caicedo, Senior Member, Technical Staff, Oracle Room 7, 12:00–13:00 Lambda: A Peek Under the Hood, Brian Goetz, Software Architect, Oracle Room 8, 12:00–13:00 In Full Flow: Java 8 Lambdas in the Stream, Paul Sandoz, Software Developer, Oracle Room 8, 14:00–15:00 The Modular Java Platform and Project Jigsaw, Mark Reinhold, Chief Architect, Java Platform Group, Oracle, Room 8, 15:10–16:10 The Curious Case of JavaScript on the JVM, Attila Szegedi, Principal Member, Technical Staff, Oracle, Room 5, 16:40–17:40 Is It a Car? Is It a Computer? No, It’s a Raspberry Pi JavaFX Informatics System. Simon Ritter, Principal Technology Evangelist, Oracle Room 7, 16:40–17:40 Thursday 14 November Java EE 7: What’s New in the Java EE Platform Linda DeMichiel, Consulting Member, Technical Staff, Oracle, Room 8, 10:50–11:50 Java Microbenchmark Harness: The Lesser of the Two Evils, Aleksey Shipilev, Principal Member, Technical Staff, Oracle. Room 6, 14:00–15:00 Practical Restful Persistence, Shaun Smith, Senior Principal Product Manager, Oracle Room 8, 17:50–18:50 Friday 15 November Avatar.js, Server-Side JavaScript on the Java Platform, Jean-Francois Denise, Software Developer, Oracle Room 8, 11:50–12:50

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  • New January 2013 Release of the Ajax Control Toolkit

    - by Stephen.Walther
    I am super excited to announce the January 2013 release of the Ajax Control Toolkit! I have one word to describe this release and that word is “Charts” – we’ve added lots of great new chart controls to the Ajax Control Toolkit. You can download the new release directly from http://AjaxControlToolkit.CodePlex.com – or, just fire the following command from the Visual Studio Library Package Manager Console Window (NuGet): Install-Package AjaxControlToolkit You also can view the new chart controls by visiting the “live” Ajax Control Toolkit Sample Site. 5 New Ajax Control Toolkit Chart Controls The Ajax Control Toolkit contains five new chart controls: the AreaChart, BarChart, BubbleChart, LineChart, and PieChart controls. Here is a sample of each of the controls: AreaChart: BarChart: BubbleChart: LineChart: PieChart: We realize that people love to customize the appearance of their charts so all of the chart controls include properties such as color properties. The chart controls render the chart on the browser using SVG. The chart controls are compatible with any browser which supports SVG including Internet Explorer 9 and new and recent versions of Google Chrome, Mozilla Firefox, and Apple Safari. (If you attempt to display a chart on a browser which does not support SVG then you won’t get an error – you just won’t get anything). Updates to the HTML Sanitizer If you are using the HtmlEditorExtender on a public-facing website then it is really important that you enable the HTML Sanitizer to prevent Cross-Site Scripting (XSS) attacks. The HtmlEditorExtender uses the HTML Sanitizer by default. The HTML Sanitizer strips out any suspicious content (like JavaScript code and CSS expressions) from the HTML submitted with the HtmlEditorExtender. We followed the recommendations of OWASP and ha.ckers.org to identify suspicious content. We updated the HTML Sanitizer with this release to protect against new types of XSS attacks. The HTML Sanitizer now has over 220 unit tests. The Ajax Control Toolkit team would like to thank Gil Cohen who helped us identify and block additional XSS attacks. Change in Ajax Control Toolkit Version Format We ran out of numbers. The Ajax Control Toolkit was first released way back in 2006. In previous releases, the version of the Ajax Control Toolkit followed the format: Release Year + Date. So, the previous release was 60919 where 6 represented the 6th release year and 0919 represent September 19. Unfortunately, the AssembyVersion attribute uses a UInt16 data type which has a maximum size of 65,534. The number 70123 is bigger than 65,534 so we had to change our version format with this release. Fortunately, the AssemblyVersion attribute actually accepts four UInt16 numbers so we used another one. This release of the Ajax Control Toolkit is officially version 7.0123. This new version format should work for another 65,000 years. And yes, I realize that 7.0123 is less than 60,919, but we ran out of numbers. Summary I hope that you find the chart controls included with this latest release of the Ajax Control Toolkit useful. Let me know if you use them in applications that you build. And, let me know if you run into any issues using the new chart controls. Next month, back to improving the File Upload control – more exciting stuff.

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  • Formal Languages, Inductive Proofs &amp; Regular Expressions

    - by MarkPearl
    So I am slogging away at my UNISA stuff. I have just finished doing the initial once non stop read through the first 11 chapters of my COS 201 Textbook - “Introduction to Computer Theory 2nd Edition” by Daniel Cohen. It has been an interesting couple of days, with familiar concepts coming up as well as some new territory. In this posting I am going to cover the first couple of chapters of the book. Let start with Formal Languages… What exactly is a formal language? Pretty much a no duh question for me but still a good one to ask – a formal language is a language that is defined in a precise mathematical way. Does that mean that the English language is a formal language? I would say no – and my main motivation for this is that one can have an English sentence that is correct grammatically that is also ambiguous. For example the ambiguous sentence: "I once shot an elephant in my pyjamas.” For this and possibly many other reasons that I am unaware of, English is termed a “Natural Language”. So why the importance of formal languages in computer science? Again a no duh question in my mind… If we want computers to be effective and useful tools then we need them to be able to evaluate a series of commands in some form of language that when interpreted by the device no confusion will exist as to what we were requesting. Imagine the mayhem that would exist if a computer misinterpreted a command to print a document and instead decided to delete it. So what is a Formal Language made up of… For my study purposes a language is made up of a finite alphabet. For a formal language to exist there needs to be a specification on the language that will describe whether a string of characters has membership in the language or not. There are two basic ways to do this: By a “machine” that will recognize strings of the language (e.g. Finite Automata). By a rule that describes how strings of a language can be formed (e.g. Regular Expressions). When we use the phrase “string of characters”, we can also be referring to a “word”. What is an Inductive Proof? So I am not to far into my textbook and of course it starts referring to proofs and different types. I have had to go through several different approaches of proofs in the past, but I can never remember their formal names , so when I saw “inductive proof” I thought to myself – what the heck is that? Google to the rescue… An inductive proof is like a normal proof but it employs a neat trick which allows you to prove a statement about an arbitrary number n by first proving it is true when n is 1 and then assuming it is true for n=k and showing it is true for n=k+1. The idea is that if you want to show that someone can climb to the nth floor of a fire escape, you need only show that you can climb the ladder up to the fire escape (n=1) and then show that you know how to climb the stairs from any level of the fire escape (n=k) to the next level (n=k+1). Does this sound like a form of recursion? No surprise then that in the same chapter they deal with recursive definitions. An example of a recursive definition for the language EVEN would the 3 rules below: 2 is in EVEN If x is in EVEN then so is x+2 The only elements in the set EVEN are those that be produced by the rules above. Nothing to exciting… So if a definition for a language is done recursively, then it makes sense that the language can be proved using induction. Regular Expressions So I am wondering to myself what use is this all – in fact – I find this the biggest challenge to any university material is that it is quite hard to find the immediate practical applications of some theory in real life stuff. How great was my joy when I suddenly saw the word regular expression being introduced. I had been introduced to regular expressions on Stack Overflow where I was trying to recognize if some text measurement put in by a user was in a valid form or not. For instance, the imperial system of measurement where you have feet and inches can be represented in so many different ways. I had eventually turned to regular expressions as an easy way to check if my parser could correctly parse the text or not and convert it to a normalize measurement. So some rules about languages and regular expressions… Any finite language can be represented by at least one if not more regular expressions A regular expressions is almost a rule syntax for expressing how regular languages can be formed regular expressions are cool For a regular expression to be valid for a language it must be able to generate all the words in the language and no other words. This is important. It doesn’t help me if my regular expression parses 100% of my measurement texts but also lets one or two invalid texts to pass as well. Okay, so this posting jumps around a bit – but introduces some very basic fundamentals for the subject which will be built on in later postings… Time to go and do some practical examples now…

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