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  • Bayes Misclassification error and plot : pattern recognition [closed]

    - by user1214586
    Below is a Matlab code for Bayes classifier which classifies arbitrary numbers into their classes. training = [3;5;17;19;24;27;31;38;45;48;52;56;66;69;73;78;84;88]; target_class = [0;0;10;10;20;20;30;30;40;40;50;50;60;60;70;70;80;80]; test = [1:2:90]'; class = classify(test,training, target_class, 'diaglinear'); % Naive Bayes classifier [test class] If someone could provide code snippets for calculating the Bayes error for misclassification and accuracy.Also, is it possible to plot a scatter plot and histogram indicating the number of data points belonging to different classes? Thank you.

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  • Should I reuse variables?

    - by IAdapter
    Should I reuse variables? I know that many best practice say you should not do it, however later when different developer is debugging the code and have 3 variables that look a like and only difference is that they are created in different places in the code he might be confused. unit-testing is a great example of this. However I do know that best practice are most of the time against it. For example they say not to "overide" method parameters. Best practice are even are against nulling the previous variables (in Java there is Sonar that has warning when you assign null to variable that you don't need to do it to call garbage collector since Java6. you cant always control what warnings are turned off, most of the time the default is on)

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  • Electronic Door Lock Uses QR Codes As Keys

    - by Jason Fitzpatrick
    We’ve seen magnetic cards and RFID cards used as keys before, but QR codes? Check out the video to see how a group of Cornell University students developed a visual key card. Rather than use magnetic stripes or RFID proximity antennas, their build relies on decoding a passkey stored in a QR code–check out the above video to see it in action and hit up the link below for more information. QR Code Door Lock [via Hack A Day] How To Create a Customized Windows 7 Installation Disc With Integrated Updates How to Get Pro Features in Windows Home Versions with Third Party Tools HTG Explains: Is ReadyBoost Worth Using?

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  • When to use HTTP status code 404 in an API

    - by Sybiam
    I am working on a project and after arguing with people at work for about more than a hour. I decided to know what people on stack-exchange might say. We're writing an API for a system, there is a query that should return a tree of Organization or a tree of Goals. The tree of Organization is the organization in which the user is present, In other words, this tree should always exists. In the organization, a tree of goal should be always present. (that's where the argument started). In case where the tree doesn't exist, my co-worker decided that it would be right to answer response with status code 200. And then started asking me to fix my code because the application was falling apart when there is no tree. I'll try to spare flames and fury. I suggested to raise a 404 error when there is no tree. It would at least let me know that something is wrong. When using 200, I have to add special check to my response in the success callback to handle errors. I'm expecting to receive an object, but I may actually receive an empty response because nothing is found. It sounds totally fair to mark the response as a 404. And then war started and I got the message that I didn't understand HTTP status code schema. So I'm here and asking what's wrong with 404 in this case? I even got the argument "It found nothing, so it's right to return 200". I believe that it's wrong since the tree should be always present. If we found nothing and we are expecting something, it should be a 404. More info, I forgot to add the urls that are fetched. Organizations /OrgTree/Get Goals /GoalTree/GetByDate?versionDate=... /GoalTree/GetById?versionId=... My mistake, both parameters are required. If any versionDate that can be parsed to a date is provided, it will return the closes revision. If you enter something in the past, it will return the first revision. If by Id with a id that doesn't exists, I suspect it's going to return an empty response with 200. Extra Also, I believe the best answer to the problem is to create default objects when organizations are created, having no tree shouldn't be a valid case and should be seen as an undefined behavior. There is no way an account can be used without both trees. For that reasons, they should be always present. also I got linked this (one similar but I can't find it) http://viswaug.files.wordpress.com/2008/11/http-headers-status1.png

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  • Sniffing out SQL Code Smells: Inconsistent use of Symbolic names and Datatypes

    - by Phil Factor
    It is an awkward feeling. You’ve just delivered a database application that seems to be working fine in production, and you just run a few checks on it. You discover that there is a potential bug that, out of sheer good chance, hasn’t kicked in to produce an error; but it lurks, like a smoking bomb. Worse, maybe you find that the bug has started its evil work of corrupting the data, but in ways that nobody has, so far detected. You investigate, and find the damage. You are somehow going to have to repair it. Yes, it still very occasionally happens to me. It is not a nice feeling, and I do anything I can to prevent it happening. That’s why I’m interested in SQL code smells. SQL Code Smells aren’t necessarily bad practices, but just show you where to focus your attention when checking an application. Sometimes with databases the bugs can be subtle. SQL is rather like HTML: the language does its best to try to carry out your wishes, rather than to be picky about your bugs. Most of the time, this is a great benefit, but not always. One particular place where this can be detrimental is where you have implicit conversion between different data types. Most of the time it is completely harmless but we’re  concerned about the occasional time it isn’t. Let’s give an example: String truncation. Let’s give another even more frightening one, rounding errors on assignment to a number of different precision. Each requires a blog-post to explain in detail and I’m not now going to try. Just remember that it is not always a good idea to assign data to variables, parameters or even columns when they aren’t the same datatype, especially if you are relying on implicit conversion to work its magic.For details of the problem and the consequences, see here:  SR0014: Data loss might occur when casting from {Type1} to {Type2} . For any experienced Database Developer, this is a more frightening read than a Vampire Story. This is why one of the SQL Code Smells that makes me edgy, in my own or other peoples’ code, is to see parameters, variables and columns that have the same names and different datatypes. Whereas quite a lot of this is perfectly normal and natural, you need to check in case one of two things have gone wrong. Either sloppy naming, or mixed datatypes. Sure it is hard to remember whether you decided that the length of a log entry was 80 or 100 characters long, or the precision of a number. That is why a little check like this I’m going to show you is excellent for tidying up your code before you check it back into source Control! 1/ Checking Parameters only If you were just going to check parameters, you might just do this. It simply groups all the parameters, either input or output, of all the routines (e.g. stored procedures or functions) by their name and checks to see, in the HAVING clause, whether their data types are all the same. If not, it lists all the examples and their origin (the routine) Even this little check can occasionally be scarily revealing. ;WITH userParameter AS  ( SELECT   c.NAME AS ParameterName,  OBJECT_SCHEMA_NAME(c.object_ID) + '.' + OBJECT_NAME(c.object_ID) AS ObjectName,  t.name + ' '     + CASE     --we may have to put in the length            WHEN t.name IN ('char', 'varchar', 'nchar', 'nvarchar')             THEN '('               + CASE WHEN c.max_length = -1 THEN 'MAX'                ELSE CONVERT(VARCHAR(4),                    CASE WHEN t.name IN ('nchar', 'nvarchar')                      THEN c.max_length / 2 ELSE c.max_length                    END)                END + ')'         WHEN t.name IN ('decimal', 'numeric')             THEN '(' + CONVERT(VARCHAR(4), c.precision)                   + ',' + CONVERT(VARCHAR(4), c.Scale) + ')'         ELSE ''      END  --we've done with putting in the length      + CASE WHEN XML_collection_ID <> 0         THEN --deal with object schema names             '(' + CASE WHEN is_XML_Document = 1                    THEN 'DOCUMENT '                    ELSE 'CONTENT '                   END              + COALESCE(               (SELECT QUOTENAME(ss.name) + '.' + QUOTENAME(sc.name)                FROM sys.xml_schema_collections sc                INNER JOIN Sys.Schemas ss ON sc.schema_ID = ss.schema_ID                WHERE sc.xml_collection_ID = c.XML_collection_ID),'NULL') + ')'          ELSE ''         END        AS [DataType]  FROM sys.parameters c  INNER JOIN sys.types t ON c.user_Type_ID = t.user_Type_ID  WHERE OBJECT_SCHEMA_NAME(c.object_ID) <> 'sys'   AND parameter_id>0)SELECT CONVERT(CHAR(80),objectName+'.'+ParameterName),DataType FROM UserParameterWHERE ParameterName IN   (SELECT ParameterName FROM UserParameter    GROUP BY ParameterName    HAVING MIN(Datatype)<>MAX(DataType))ORDER BY ParameterName   so, in a very small example here, we have a @ClosingDelimiter variable that is only CHAR(1) when, by the looks of it, it should be up to ten characters long, or even worse, a function that should be a char(1) and seems to let in a string of ten characters. Worth investigating. Then we have a @Comment variable that can't decide whether it is a VARCHAR(2000) or a VARCHAR(MAX) 2/ Columns and Parameters Actually, once we’ve cleared up the mess we’ve made of our parameter-naming in the database we’re inspecting, we’re going to be more interested in listing both columns and parameters. We can do this by modifying the routine to list columns as well as parameters. Because of the slight complexity of creating the string version of the datatypes, we will create a fake table of both columns and parameters so that they can both be processed the same way. After all, we want the datatypes to match Unfortunately, parameters do not expose all the attributes we are interested in, such as whether they are nullable (oh yes, subtle bugs happen if this isn’t consistent for a datatype). We’ll have to leave them out for this check. Voila! A slight modification of the first routine ;WITH userObject AS  ( SELECT   Name AS DataName,--the actual name of the parameter or column ('@' removed)  --and the qualified object name of the routine  OBJECT_SCHEMA_NAME(ObjectID) + '.' + OBJECT_NAME(ObjectID) AS ObjectName,  --now the harder bit: the definition of the datatype.  TypeName + ' '     + CASE     --we may have to put in the length. e.g. CHAR (10)           WHEN TypeName IN ('char', 'varchar', 'nchar', 'nvarchar')             THEN '('               + CASE WHEN MaxLength = -1 THEN 'MAX'                ELSE CONVERT(VARCHAR(4),                    CASE WHEN TypeName IN ('nchar', 'nvarchar')                      THEN MaxLength / 2 ELSE MaxLength                    END)                END + ')'         WHEN TypeName IN ('decimal', 'numeric')--a BCD number!             THEN '(' + CONVERT(VARCHAR(4), Precision)                   + ',' + CONVERT(VARCHAR(4), Scale) + ')'         ELSE ''      END  --we've done with putting in the length      + CASE WHEN XML_collection_ID <> 0 --tush tush. XML         THEN --deal with object schema names             '(' + CASE WHEN is_XML_Document = 1                    THEN 'DOCUMENT '                    ELSE 'CONTENT '                   END              + COALESCE(               (SELECT TOP 1 QUOTENAME(ss.name) + '.' + QUOTENAME(sc.Name)                FROM sys.xml_schema_collections sc                INNER JOIN Sys.Schemas ss ON sc.schema_ID = ss.schema_ID                WHERE sc.xml_collection_ID = XML_collection_ID),'NULL') + ')'          ELSE ''         END        AS [DataType],       DataObjectType  FROM   (Select t.name AS TypeName, REPLACE(c.name,'@','') AS Name,          c.max_length AS MaxLength, c.precision AS [Precision],           c.scale AS [Scale], c.[Object_id] AS ObjectID, XML_collection_ID,          is_XML_Document,'P' AS DataobjectType  FROM sys.parameters c  INNER JOIN sys.types t ON c.user_Type_ID = t.user_Type_ID  AND parameter_id>0  UNION all  Select t.name AS TypeName, c.name AS Name, c.max_length AS MaxLength,          c.precision AS [Precision], c.scale AS [Scale],          c.[Object_id] AS ObjectID, XML_collection_ID,is_XML_Document,          'C' AS DataobjectType            FROM sys.columns c  INNER JOIN sys.types t ON c.user_Type_ID = t.user_Type_ID   WHERE OBJECT_SCHEMA_NAME(c.object_ID) <> 'sys'  )f)SELECT CONVERT(CHAR(80),objectName+'.'   + CASE WHEN DataobjectType ='P' THEN '@' ELSE '' END + DataName),DataType FROM UserObjectWHERE DataName IN   (SELECT DataName FROM UserObject   GROUP BY DataName    HAVING MIN(Datatype)<>MAX(DataType))ORDER BY DataName     Hmm. I can tell you I found quite a few minor issues with the various tabases I tested this on, and found some potential bugs that really leap out at you from the results. Here is the start of the result for AdventureWorks. Yes, AccountNumber is, for some reason, a Varchar(10) in the Customer table. Hmm. odd. Why is a city fifty characters long in that view?  The idea of the description of a colour being 256 characters long seems over-ambitious. Go down the list and you'll spot other mistakes. There are no bugs, but just mess. We started out with a listing to examine parameters, then we mixed parameters and columns. Our last listing is for a slightly more in-depth look at table columns. You’ll notice that we’ve delibarately removed the indication of whether a column is persisted, or is an identity column because that gives us false positives for our code smells. If you just want to browse your metadata for other reasons (and it can quite help in some circumstances) then uncomment them! ;WITH userColumns AS  ( SELECT   c.NAME AS columnName,  OBJECT_SCHEMA_NAME(c.object_ID) + '.' + OBJECT_NAME(c.object_ID) AS ObjectName,  REPLACE(t.name + ' '   + CASE WHEN is_computed = 1 THEN ' AS ' + --do DDL for a computed column          (SELECT definition FROM sys.computed_columns cc           WHERE cc.object_id = c.object_id AND cc.column_ID = c.column_ID)     --we may have to put in the length            WHEN t.Name IN ('char', 'varchar', 'nchar', 'nvarchar')             THEN '('               + CASE WHEN c.Max_Length = -1 THEN 'MAX'                ELSE CONVERT(VARCHAR(4),                    CASE WHEN t.Name IN ('nchar', 'nvarchar')                      THEN c.Max_Length / 2 ELSE c.Max_Length                    END)                END + ')'       WHEN t.name IN ('decimal', 'numeric')       THEN '(' + CONVERT(VARCHAR(4), c.precision) + ',' + CONVERT(VARCHAR(4), c.Scale) + ')'       ELSE ''      END + CASE WHEN c.is_rowguidcol = 1          THEN ' ROWGUIDCOL'          ELSE ''         END + CASE WHEN XML_collection_ID <> 0            THEN --deal with object schema names             '(' + CASE WHEN is_XML_Document = 1                THEN 'DOCUMENT '                ELSE 'CONTENT '               END + COALESCE((SELECT                QUOTENAME(ss.name) + '.' + QUOTENAME(sc.name)                FROM                sys.xml_schema_collections sc                INNER JOIN Sys.Schemas ss ON sc.schema_ID = ss.schema_ID                WHERE                sc.xml_collection_ID = c.XML_collection_ID),                'NULL') + ')'            ELSE ''           END + CASE WHEN is_identity = 1             THEN CASE WHEN OBJECTPROPERTY(object_id,                'IsUserTable') = 1 AND COLUMNPROPERTY(object_id,                c.name,                'IsIDNotForRepl') = 0 AND OBJECTPROPERTY(object_id,                'IsMSShipped') = 0                THEN ''                ELSE ' NOT FOR REPLICATION '               END             ELSE ''            END + CASE WHEN c.is_nullable = 0               THEN ' NOT NULL'               ELSE ' NULL'              END + CASE                WHEN c.default_object_id <> 0                THEN ' DEFAULT ' + object_Definition(c.default_object_id)                ELSE ''               END + CASE                WHEN c.collation_name IS NULL                THEN ''                WHEN c.collation_name <> (SELECT                collation_name                FROM                sys.databases                WHERE                name = DB_NAME()) COLLATE Latin1_General_CI_AS                THEN COALESCE(' COLLATE ' + c.collation_name,                '')                ELSE ''                END,'  ',' ') AS [DataType]FROM sys.columns c  INNER JOIN sys.types t ON c.user_Type_ID = t.user_Type_ID  WHERE OBJECT_SCHEMA_NAME(c.object_ID) <> 'sys')SELECT CONVERT(CHAR(80),objectName+'.'+columnName),DataType FROM UserColumnsWHERE columnName IN (SELECT columnName FROM UserColumns  GROUP BY columnName  HAVING MIN(Datatype)<>MAX(DataType))ORDER BY columnName If you take a look down the results against Adventureworks, you'll see once again that there are things to investigate, mostly, in the illustration, discrepancies between null and non-null datatypes So I here you ask, what about temporary variables within routines? If ever there was a source of elusive bugs, you'll find it there. Sadly, these temporary variables are not stored in the metadata so we'll have to find a more subtle way of flushing these out, and that will, I'm afraid, have to wait!

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  • How to download source code with apt-get?

    - by Muurverf
    I'm trying to download source code of certain packages, for example rhythmbox, for learning purposes. I want to do this through apt-get, with the apt-get source command. For some reason, apt-get can't seem to find any package. I've tried several packages, and I keep getting this output from apt-get: $ apt-get source rhythmbox Reading package lists... Done Building dependency tree Reading state information... Done E: Unable to find a source package for rhythmbox I've been searching for answers for quite some time now, but I can't find anyone with the same issue. apt-get works fine with installing and updating so apt-get works fine in my opinion. During the search I also learned that I had to enable the 'source code repositories' in Software Sources, so that's also enabled. I am aware of the fact that (maybe only for certain packages, not sure) source packages can also be downloaded with bzr from Launchpad, but I want to know why this method won't work. Thanks in advance!

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  • Does TDD lead to the good design?

    - by Eugen Martynov
    I'm in transition from "writing unit tests" state to TDD. I saw as Johannes Brodwall creates quite acceptable design from avoiding any of architecture phase before. I'll ask him soon if it was real improvisation or he had some thoughts upfront. I also clearly understand that everyone has experience that prevents to write explicit design bad patterns. But after participating in code retreat I hardly believe that writing test first could save us from mistakes. But I also believe that tests after code will lead to mistakes much faster. So this night question is asking for people who is using TDD for a long time share their experience about results of design without upfront thinking. If they really practice it and get mostly suitable design. Or it's my small understanding about TDD and probably agile.

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  • How to write reusable code in node.js

    - by lortabac
    I am trying to understand how to design node.js applications, but it seems there is something I can't grasp about asynchronous programming. Let's say my application needs to access a database. In a synchronous environment I would implement a data access class with a read() method, returning an associative array. In node.js, because code is executed asynchronously, this method can't return a value, so, after execution, it will have to "do" something as a side effect. It will then contain some code which does something else than just reading data. Let's suppose I want to call this method multiple times, each time with a different success callback. Since the callback is included in the method itself, I can't find a clean way to do this without either duplicating the method or specifying all possible callbacks in a long switch statement. What is the proper way to handle this problem? Am I approaching it the wrong way?

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  • How do you dive into large code bases?

    - by miku
    What tools and techniques do you use for exploring and learning an unknown code base? I am thinking of tools like grep, ctags, unit-tests, functional test, class-diagram generators, call graphs, code metrics like sloccount and so on. I'd be interested in your experiences, the helpers you used or wrote yourself and the size of the codebase, with which you worked with. I realize, that this is also a process (happening over time) and that learning can mean "can give a ten minute intro" to "can refactor and shrink this to 30% of the size". Let's leave that open for now.

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  • Colleague unwilling to use unit tests "as it's more to code"

    - by m.edmondson
    A colleague is unwilling to use unit tests and instead opting for a quick test, pass it to the users, and if all is well it is published live. Needless to say some bugs do get through. I mentioned we should think about using unit tests - but she was all against it once it was realised more code would have to be written. This leaves me in the position of modifying something and not being sure the output is the same, especially as her code is spaghetti and I try to refactor it when I get a chance. So whats the best way forward for me?

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  • If Expression True in Immediate Window But Code In if Block Never Runs

    - by Julian
    I set a break point in my code in MonoDevelop to break whenever I click on a surface. I then enter the immediate window and test to see if the the if statement will return true in comparing two Vector3's. It does return true. However, when I step over, the code is never run as though the statement evaluated false. Does anyone know how this could be possible? I've attached a screenshot. Here is the picture of my debug window and immediate window. You can see where the immediate window evaluates to true. The second breakpoint is not hit. Here are the details of the two Vector3's I am comparing. Does anyone know why I am experiencing this? It really seems like an anomaly to me :/ Does it have something to do with threading?

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  • How and where do you store your private work/sourcecode?

    - by Amir Rezaei
    I have worked as a developer for over 10 years now. During that time I have had my own small projects where I have developed tools, applications and games. I have not found any robust solution to store my work. It’s always fun to get back to your code and see how you did before and how you would do it now. It’s just work that is unfortunate to lose. There are SVN solution such as Google’s Project Hosting. However I’m not interested in sharing my code or making it open source. Currently I’m hosting my own SVN server. So here comes my question: How and where do you store your private work/sourcecode? Requirements: Sourcecode versioning Backup Prefers free Edit: Remote access Edit: I have used Dropbox + TrueCrypt + SVN. Unfortunately you are limited to 5gb.

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  • .NET - refactoring code

    - by w0051977
    I have inherited and now further develop a large application consisting of an ASP.NET application, VB6 and VB.NET application. The software was poorly written. I am trying to refactor the code as I go along. The changes I am making are not live (they are contained in a folder on my development machine). This is proving to be time consuming and I am doing this along side other work which is the prioritiy. My question is: is this a practical approach or is there a better methodology for refactoring code? I don't have any experience with version control software or source control software and I am wandering if this is what I am missing. I am a sole developer.

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  • How do you dive into large code bases?

    - by miku
    What tools and techniques do you use for exploring and learning an unknown code base? I am thinking of tools like grep, ctags, unit-tests, functional test, class-diagram generators, call graphs, code metrics like sloccount and so on. I'd be interested in your experiences, the helpers you used or wrote yourself and the size of the codebase, with which you worked with. I realize, that this is also a process (happening over time) and that learning can mean "can give a ten minute intro" to "can refactor and shrink this to 30% of the size". Let's leave that open for now.

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  • Coordinating team code review sessions

    - by Wade Tandy
    My question has two parts: 1) In your team or organization, do you ever do in-person code reviews with all or part of a team, as opposed to online reviews using some sort of tool? 2) How do you structure these meetings? Do you choose to focus on one person's code in a given meeting? Do you look at everything? Take a random sample? Ask people on the team what they'd like to have looked at of theirs? I'd love to add this practice to my development team, so I'd like to hear how others are doing it.

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  • managing information/functionality on shared common project classes

    - by ilansch
    In my company, we have a common solution the contains common projects (2 projects so far, one for .net 3.5 and one for .net 4.5). My main problem is that during time, a lot of code is added, for example hosting a process as windows service is a class called ServiceManagement, But no one but the developer knows it, and if someone wants to use this shared class, he does not know it exist. So i am looking for a way to document and manage all the classes with tags, a 3rd party util/web util, that i can search for tags and maybe find common classes that i can use (if we keep all our code well-documented). Does anyone familiar with sort of tools ?

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  • Difference between jquery.clone() and simple concatenation of string [closed]

    - by Francis Cebu
    Which of the following code samples is faster in generating HTML code using jQuery? Sample 1: var div = $("<div>"); $.each(data,function(count,item){ var Elem = div.clone().addClass("message").html(item.Firstname); $(".container").append(Elem); }); Sample 2: $.each(data,function(count,item){ var Elem = "<div class = 'Elem'>" + item.Firstname + "</div>"; $(".container").append(Elem); });

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  • How to set up a one-man research in the difference between BDD and Waterfall?

    - by Martijn van der Maas
    Earlier, I asked a question about how to measure the quality of a project. The outcome of that question was that the quality of the project can be divided into two parts: Internal quality (code quality, measurable by code quality metrics) External quality (Acceptance test, how well the software meets the requirements) So based on that, I want to set up some research and validate the outcome of the project. The problem is, I will conduct this research on my own, so it's not possible to run the project once in BDD style and the other one in waterfall by myself. It's also not possible to compare BDD and waterfall projects on a larger scale, due to the fact that there are not enough BDD projects that can be measured because of the age of BDD. So, my question is: did anybody face this problem? How could I execute my experiment in such a way that it is of scientific value?

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  • CQRS at Jax Code Camp 2012

    - by brian_ritchie
    Continuing my CQRS world tour...I gave my CQRS presentation at the Jax Code Camp 2012 this past Saturday.  It was a great crowd with lots of representation from the wicked smart engineers at Feature[23] and others from the Jacksonville developer community. If you'd like to take a look at my slide deck, they are out on SlideShare. The code I demoed is from Ashic Mahtab and is posted on github.   If you can't get enough of CQRS, Microsoft has joined the CQRS party with their CQRS Journey which includes a free e-book called Exploring CQRS and Event Sourcing.

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