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  • Relational vs. Dimensional Databases, what's the difference?

    - by grautur
    I'm trying to learn about OLAP and data warehousing, and I'm confused about the difference between relational and dimensional modeling. Is dimensional modeling basically relational modeling, but allowing for redundant/un-normalized data? For example, let's say I have historical sales data on (product, city, # sales). I understand that the following would be a relational point-of-view: Product | City | # Sales Apples, San Francisco, 400 Apples, Boston, 700 Apples, Seattle, 600 Oranges, San Francisco, 550 Oranges, Boston, 500 Oranges, Seattle, 600 While the following is a more dimensional point-of-view: Product | San Francisco | Boston | Seattle Apples, 400, 700, 600 Oranges, 550, 500, 600 But it seems like both points of view would nonetheless be implemented in an identical star schema: Fact table: Product ID, Region ID, # Sales Product dimension: Product ID, Product Name City dimension: City ID, City Name And it's not until you start adding some additional details to each dimension that the differences start popping up. For instance, if you wanted to track regions as well, a relational database would tend to have a separate region table, in order to keep everything normalized: City dimension: City ID, City Name, Region ID Region dimension: Region ID, Region Name, Region Manager, # Regional Stores While a dimensional database would allow for denormalization to keep the region data inside the city dimension, in order to make it easier to slice the data: City dimension: City ID, City Name, Region Name, Region Manager, # Regional Stores Is this correct?

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  • Why "alt" attribute for <img> tag has been considered mandatory by the HTML validator .. ?

    - by infant programmer
    Is there any logical or technical reason (with the W3C validation) for making alt as required attribute .. This is my actual problem:though my page is perfect enough with respect to W3C validation rules .. Only error I am getting is line XX column YY - Error: required attribute "ALT" not specified I know the significance of "alt" attribute and I have omitted that where it is unnecessary .. (to be more elaborate .. I have added the image to increase the beauty of my page and I don't want alt attribute to show irrelevant message to the viewer) getting rid of the error is secondary .. rather I am curious to know whether is it a flaw with validation rules .. ?? I thank stackOverflow and all the members who responded me .. I got my doubt clarified .. :-)

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  • good way to implement NotSpecification: isSpecialCaseOf?

    - by koen
    I'm implementing the specification pattern. The NotSpecification seems simple at first: NotSpecification.IsSpecialCaseOf(otherSpecification) return !this.specification.isSpecialCaseOf(otherSpecification) But it doesn't work for all Specifications: Not(LesserThan(5)).IsSpecialCaseOf(GreaterThan(4)) This should be true. So far I think that the only way to accomplish the isSpecialCaseOf the NotSpecification is to implement the remainderUnsatisfiedBy (partial subsumption in the paper on the specification pattern). But maybe I am missing something more simple or a logical insight that makes this unnecessary. Question: Is there another way of implementing this by not using remainderUnsatisfiedBy?

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  • Implementation of a general-purpose object structure (property bag)

    - by Thomas Wanner
    We need to implement some general-purpose object structure, much like an object in dynamic languages, that would give us a possibility of creating the whole object graph on-the-fly. This class has to be serializable and somehow user friendly. So far we have made some experiments with class derived from Dictionary<string, object> using the dot notation path to store properties and collections in the object tree. We have also find an article that implements something similar, but it doesn't seem to fit completely into our picture either. Do you know about some good implementations / libraries that deal with a similar problem or do you have any (non-trivial) ideas that could help us with our own implementation ? Also, I probably have to say that we are using .NET 3.5, so we can't take advantage of the new features in .NET 4.0 like dynamic type etc. (as far as I know it's also not possible to use any subset of it in .NET 3.5 solution).

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  • Optimize mysql table ?

    - by fabien-barbier
    Here is my actual table schema (I'm using Mysql) : Table experiment : code(int) sample_1_id sample_2_id ... until ... sample_12_id rna_1_id rna_2_id ... until ... rna_12_id experiment_start How can I optimize both part : sample_n_id and rna_n_id (all are bigint(20) and allow null=true) ? About values : we can have : ex : sample_1_id = 2 , Sample_2_id = 5 , ... Note : values can be updated. Ideas ? Thanks.

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  • C# Setting Properties using Index

    - by Guazz
    I have a business class that contains many properties for various stock-exchange price types. This is a sample of the class: public class Prices { public decimal Today {get; set} public decimal OneDay {get; set} public decimal SixDay {get; set} public decimal TenDay {get; set} public decimal TwelveDay {get; set} public decimal OneDayAdjusted {get; set;} public decimal SixDayAdjusted {get; set;} public decimal TenDayAdjusted {get; set;} public decimal OneHundredDayAdjusted {get; set;} } I have a legacy system that supplies the prices using string ids to identify the price type. E.g. Today = "0D" OneDay = "1D" SixDay = "6D" //..., etc. Firstly, I load all the values to an IDictionary() collection so we have: [KEY] VALUE [0D] = 1.23456 [1D] = 1.23456 [6D] = 1.23456 ...., etc. Secondly, I set the properties of the Prices class using a method that takes the above collection as a parameter like so: SetPricesValues(IDictionary<string, decimal> pricesDictionary) { // TODAY'S PRICE string TODAY = "D0"; if (true == pricesDictionary.ContainsKey(TODAY)) { this.Today = pricesDictionary[TODAY]; } // OneDay PRICE string ONE_DAY = "D1"; if (true == pricesDictionary.ContainsKey(ONE_DAY)) { this.OneDay = pricesDictionary[ONE_DAY]; } //..., ..., etc., for each other property } Is there a more elegant technique to set a large amount of properties? Thanks, j

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  • DRY programming dilemma

    - by fayer
    the situation is like this: im creating a Logger class that can write to a file but the write_to_file() function is in a helper class as a static function. i could call that function but then the Log class would be dependent to the helper class. isn't dependency bad? but if i can let it use a helper function then what is the point of having helper functions? what should one prioritize here: using helper functions and have to include this helper class everywhere (but the other 99 methods wont be useful) or just copy and paste into the Log class (but then if i have done this 100 times and then make a change i have to change in 100 places). share your thoughts and experience!

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  • Business Layer Pattern on Rails? MVCL

    - by Fabiano PS
    That is a broad question, and I appreciate no short/dumb asnwers like: "Oh that is the model job, this quest is retarded (period)" PROBLEM Where I work at people created a system over 2 years for managing the manufacture process over demand in the most simplified still broad as possible, involving selling, buying, assemble, The system is coded over Ruby On Rails. The result has been changed lots of times and the result is a mess on callbacks (some are called several times), 200+ models, and fat controllers: Total bad. The QUESTION is, if there is a gem, or pattern designed to handle Rails large app logic? The logic whould be able to fully talk to models (whose only concern would be data format handling and validation) What I EXPECT is to reduce complexity from various controllers, and hard to track callbacks into files with the responsibility to handle a business operation logic. In some cases there is the need to wait for a response, in others, only validation of the input is enough and a bg process would take place. ie: -- Sell some products (need to wait the operation to finish) 1. Set a View able to get the products input 2. Controller gets the product list inputed by employee and call the logic Logic::ExecuteWithResponse('sell', 'products', :prods => @product_list_with_qtt, :when => @date, :employee => current_user() ) This Logic would handle buying order, assemble order, machine schedule, warehouse reservation, and others

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  • How to avoid using this in a contructor

    - by Paralife
    I have this situation: interface MessageListener { void onMessageReceipt(Message message); } class MessageReceiver { MessageListener listener; public MessageReceiver(MessageListener listener, other arguments...) { this.listener = listener; } loop() { Message message = nextMessage(); listener.onMessageReceipt(message); } } and I want to avoid the following pattern: (Using the this in the Client constructor) class Client implements MessageListener { MessageReceiver receiver; MessageSender sender; public Client(...) { receiver = new MessageReceiver(this, other arguments...); sender = new Sender(...); } . . . @Override public void onMessageReceipt(Message message) { if(Message.isGood()) sender.send("Congrtulations"); else sender.send("Boooooooo"); } } The reason why i need the above functionality is because i want to call the sender inside the onMessageReceipt() function, for example to send a reply. But I dont want to pass the sender into a listener, so the only way I can think of is containing the sender in a class that implements the listener, hence the above resulting Client implementation. Is there a way to achive this without the use of 'this' in the constructor? It feels bizare and i dont like it, since i am passing myself to an object(MessageReceiver) before I am fully constructed. On the other hand, the MessageReceiver is not passed from outside, it is constructed inside, but does this 'purifies' the bizarre pattern? I am seeking for an alternative or an assurance of some kind that this is safe, or situations on which it might backfire on me.

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  • Objective-C partial implementation of classes in separate files

    - by Aran Mulholland
    I am using core data and am generating classes from my data model. I implement custom methods in these classes, however when i regenerate i generate over the top so i end up copying and pasting a bit. What i would like to do is split my implementation files ('.m') so i can have one header file with multiple '.m' files. then i can keep my custom methods in one and not have to worry about erasing them when i regenerate. I use this technique in .NET a lot with its partial keyword. Is there anything similar in objective-C

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  • Confused about this factory, as it doesn't look like an Abstract Factory nor Factory Method

    - by Pin
    I'm looking into Guice and I've been reading its documentation recently. Reading the motivation section I don't understand the factories part, why they name it that way. To me that factory is just a wrapper for the implementing class they want it to return after calling getInstance(). public class CreditCardProcessorFactory { private static CreditCardProcessor instance; public static void setInstance(CreditCardProcessor creditCardProcessor) { instance = creditCardProcessor; } public static CreditCardProcessor getInstance() { if (instance == null) { throw new IllegalStateException("CreditCardProcessorFactory not initialized. " + "Did you forget to call CreditCardProcessor.setInstance() ?"); } return instance; } } Why do they call it factory as well if it is neither an abstract factory nor a factory method? Or am I missing something? Thanks.

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  • When should a member function have a const qualifier and when shouldn't it?

    - by SCFrench
    About six years ago, a software engineer named Harri Porten wrote this article, asking the question, "When should a member function have a const qualifier and when shouldn't it?" I found it to be the best write-up I could find of the issue, which I've been wrestling with more recently and which I think is not well covered in most discussions I've found on const correctness. Since a software information-sharing site as powerful as SO didn't exist back then, I'd like to resurrect the question here.

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  • Pagination For SMS in Android specifically

    - by Priyank
    Hi. I had a pagination related question posted earlier. Here I went through the posted answers and suggested choices and I realized that to implement pagination in an application I could still write db level queries and ensure that I could implement pagination, even if in a crude form. However I have few follow up questions now: I am trying to show SMS from a content provider. Suppose I don't want to use content provider; can I access SMS table in database through my application. Aoes android's security framework allow that? How do people generally handle pagination problems in android, related to content that they are not storing but instead are fetching through content providers. (Android's own or custom) Isn't this a bigger problem. I am surprised to find so little text online about it.

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  • Data access pattern

    - by andlju
    I need some advice on what kind of pattern(s) I should use for pushing/pulling data into my application. I'm writing a rule-engine that needs to hold quite a large amount of data in-memory in order to be efficient enough. I have some rather conflicting requirements; It is not acceptable for the engine to always have to wait for a full pre-load of all data before it is functional. Only fetching and caching data on-demand will lead to the engine taking too long before it is running quickly enough. An external event can trigger the need for specific parts of the data to be reloaded. Basically, I think I need a combination of pushing and pulling data into the application. A simplified version of my current "pattern" looks like this (in psuedo-C# written in notepad): // This interface is implemented by all classes that needs the data interface IDataSubscriber { void RegisterData(Entity data); } // This interface is implemented by the data access class interface IDataProvider { void EnsureLoaded(Key dataKey); void RegisterSubscriber(IDataSubscriber subscriber); } class MyClassThatNeedsData : IDataSubscriber { IDataProvider _provider; MyClassThatNeedsData(IDataProvider provider) { _provider = provider; _provider.RegisterSubscriber(this); } public void RegisterData(Entity data) { // Save data for later StoreDataInCache(data); } void UseData(Key key) { // Make sure that the data has been stored in cache _provider.EnsureLoaded(key); Entity data = GetDataFromCache(key); } } class MyDataProvider : IDataProvider { List<IDataSubscriber> _subscribers; // Make sure that the data for key has been loaded to all subscribers public void EnsureLoaded(Key key) { if (HasKeyBeenMarkedAsLoaded(key)) return; PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } // Force all subscribers to get a new version of the data for key public void ForceReload(Key key) { PublishDataToSubscribers(key); MarkKeyAsLoaded(key); } void PublishDataToSubscribers(Key key) { Entity data = FetchDataFromStore(key); foreach(var subscriber in _subscribers) { subscriber.RegisterData(data); } } } // This class will be spun off on startup and should make sure that all data is // preloaded as quickly as possible class MyPreloadingThread { IDataProvider _provider; MyPreloadingThread(IDataProvider provider) { _provider = provider; } void RunInBackground() { IEnumerable<Key> allKeys = GetAllKeys(); foreach(var key in allKeys) { _provider.EnsureLoaded(key); } } } I have a feeling though that this is not necessarily the best way of doing this.. Just the fact that explaining it seems to take two pages feels like an indication.. Any ideas? Any patterns out there I should have a look at?

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  • Collaboration Diagrams: how to represent setting a variable's and attribute's value to a specified v

    - by devoured elysium
    Let's assume I have a class called MyClass with an attribute called MyAttribute and a method called MyMethod(). Inside that method I'd like to have a variable called MyVariable. I'd like to set the value of MyVariable to "MyVariable" and MyAttribute to "MyAttribute" inside the call to MyMethod(). How can I do this in a Collaboration Diagram? I can't find any info of this kind on the internet and the book I'm studying from (Applying UML and Patterns) is very vague in the details. Thanks

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  • Best way to represent Gender in a class library used in multilingual applications

    - by Hauge
    I'm creating class library with some commonly used classes like persons, addresses etc. This library will be used in an multilingual application, and I am looking for the most convenient way to represent a persons gender. Ideally I would like to be able to code like this: Person person = new Person { Gender = Genders.Male, FirstName = "Nice", LastName = "Dude" } if (person.Gender == Genders.Male) Console.WriteLine("person is Male"); Console.WriteLine(person.Gender); //Should output: Male Console.WriteLine(person.Gender.ToString("da-DK")); //Should output the name of the gender in the language provided List<Gender> genders = Genders.GetAll(); foreach(Gender gender in genders) { Console.WriteLine(gender.ToString()); Console.WriteLine(gender.ToString("da-DK")); } What would you do? An enumeration and a specialized Gender class, but what about the localization then? Regards Jesper Hauge

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  • Sub-Schemas in SQL Server 2005/2008

    - by Maushu
    This is a simple question yet I was unable to find any information at all about this. Is it possible to have sub-schemas in SQL Server 2005/2008? Example: Having a HR (Human Resources) schema with a sub-schema called Training (with tables related to this). It would end up like HR.Training.* where * would be the tables.

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  • Making a DateTime field in SQLExpress database?

    - by Mike
    I'm putting together a simple test database to learn MVC with. I want to add a DateTime field to show when the record was CREATED. ID = int Name = Char DateCreated = (dateTime, DateTime2..?) I have a feeling that this type of DateTime capture can be done automatically - but that's all I have, a feeling. Can it be done? And if so how? While we're on the subject: if I wanted to include another field that captured the DateTime of when the record was LAST UPDATED how would I do that. I'm hoping to not do this manually. Many thanks Mike

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  • Java: initialization problem with private-final-int-value and empty constructor

    - by HH
    $ javac InitInt.java InitInt.java:7: variable right might not have been initialized InitInt(){} ^ 1 error $ cat InitInt.java import java.util.*; import java.io.*; public class InitInt { private final int right; InitInt(){} public static void main(String[] args) { // I don't want to assign any value. // just initialize it, how? InitInt test = new InitInt(); System.out.println(test.getRight()); // later assiging a value } public int getRight(){return right;} } Initialization problem with Constructor InitInt{ // Still the error, "may not be initialized" // How to initialise it? if(snippetBuilder.length()>(charwisePos+25)){ right=charwisePos+25; }else{ right=snippetBuilder.length()-1; } }

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  • Allocation algorithm help, using Python.

    - by Az
    Hi there, I've been working on this general allocation algorithm for students. The pseudocode for it (a Python implementation) is: for a student in a dictionary of students: for student's preference in a set of preferences (ordered from 1 to 10): let temp_project be the first preferred project check if temp_project is available if so, allocate it to them and make the project UNavailable to others Quite simply this will try to allocate projects by starting from their most preferred. The way it works, out of a set of say 100 projects, you list 10 you would want to do. So the 10th project wouldn't be the "least preferred overall" but rather the least preferred in their chosen set, which isn't so bad. Obviously if it can't allocate a project, a student just reverts to the base case which is an allocation of None, with a rank of 11. What I'm doing is calculating the allocation "quality" based on a weighted sum of the ranks. So the lower the numbers (i.e. more highly preferred projects), the better the allocation quality (i.e. more students have highly preferred projects). That's basically what I've currently got. Simple and it works. Now I'm working on this algorithm that tries to minimise the allocation weight locally (this pseudocode is a bit messy, sorry). The only reason this will probably work is because my "search space" as it is, isn't particularly large (just a very general, anecdotal observation, mind you). Since the project is only specific to my Department, we have their own limits imposed. So the number of students can't exceed 100 and the number of preferences won't exceed 10. for student in a dictionary/list/whatever of students: where i = 0 take the (i)st student, (i+1)nd student for their ranks: allocate the projects and set local_weighting to be sum(student_i.alloc_proj_rank, student_i+1.alloc_proj_rank) these are the cases: if local_weighting is 2 (i.e. both ranks are 1): then i += 1 and and continue above if local weighting is = N>2 (i.e. one or more ranks are greater than 1): let temp_local_weighting be N: pick student with lowest rank and then move him to his next rank and pick the other student and reallocate his project after this if temp_local_weighting is < N: then allocate those projects to the students move student with lowest rank to the next rank and reallocate other if temp_local_weighting < previous_temp_allocation: let these be the new allocated projects try moving for the lowest rank and reallocate other else: if this weighting => previous_weighting let these be the allocated projects i += 1 and move on for the rest of the students So, questions: This is sort of a modification of simulated annealing, but any sort of comments on this would be appreciated. How would I keep track of which student is (i) and which student is (i+1) If my overall list of students is 100, then the thing would mess up on (i+1) = 101 since there is none. How can I circumvent that? Any immediate flaws that can be spotted? Extra info: My students dictionary is designed as such: students[student_id] = Student(student_id, student_name, alloc_proj, alloc_proj_rank, preferences) where preferences is in the form of a dictionary such that preferences[rank] = {project_id}

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  • Objective-C Simple Inheritance and OO Principles

    - by bleeckerj
    I have a subclass SubClass that inherits from baseclass BaseClass. BaseClass has an initializer, like so: -(id)init { self = [super init]; if(self) { [self commonInit]; } return self; } -(void)commonInit { self.goodStuff = [[NSMutableArray alloc]init]; } SubClass does its initializer, like so: -(id)init { self = [super init]; if(self) { [self commonInit]; } return self; } -(void)commonInit { self.extraGoodStuff = [[NSMutableArray alloc]init]; } Now, I've *never taken a proper Objective-C course, but I'm a programmer more from the Electrical Engineering side, so I make do. I've developed server-side applications mostly in Java though, so I may be seeing the OO world through Java principles. When SubClass is initialized, it calls the BaseClass init and my expectation would be — because inheritance to me implies that characteristics of a BaseClass pass through to SubClass — that the commonInit method in BaseClass would be called during BaseClass init. It is not. I can *sorta understand maybe-possibly-stretch-my-imagination why it wouldn't be. But, then — why wouldn't it be based on the principles of OOP? What does "self" represent if not the instance of the class of the running code? Okay, so — I'm not going to argue that what a well-developed edition of Objective-C is doing is wrong. So, then — what is the pattern I should be using in this case? I want SubClass to have two main bits — the goodStuff that BaseClass has as well as the extraGoodStuff that it deserves as well. Clearly, I've been using the wrong pattern in this type of situation. Am I meant to expose commonInit (which makes me wonder about encapsulation principles — why expose something that, in the Java world at least, would be considered "protected" and something that should only ever be called once for each instance)? I've run into a similar problem in the recent past and tried to muddle through it, but now — I'm really wondering if I've got my principles and concepts all straight in my head. Little help, please.

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  • Is there a way to effect user defined data types in MySQL?

    - by Dancrumb
    I have a database which stores (among other things), the following pieces of information: Hardware IDs BIGINTs Storage Capacities BIGINTs Hardware Names VARCHARs World Wide Port Names VARCHARs I'd like to be able to capture a more refined definition of these datatypes. For instance, the hardware IDs have no numerical significance, so I don't care how they are formatted when displayed. The Storage Capacities, however, are cardinal numbers and, at a user's request, I'd like to present them with thousands and decimal separators, e.g. 123,456.789. Thus, I'd like to refine BIGINT into, say ID_NUMBER and CARDINAL. The same with Hardware Names, which are simple text and WWPNs, which are hexstrings, e.g. 24:68:AC:E0. Thus, I'd like to refine VARCHAR into ENGLISH_WORD and HEXSTRING. The specific datatypes I made up are just for illustrative purposes. I'd like to keep all this information in one place and I'm wondering if anybody knows of a good way to hold this all in my MySQL table definitions. I could use the Comment field of the table definition, but that smells fishy to me. One approach would be to define the data structure elsewhere and use that definition to generate my CREATE TABLEs, but that would be a major rework of the code that I currently have, so I'm looking for alternatives. Any suggestions? The application language in use is Perl, if that helps.

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