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  • NoSQL vs Relational Coding Styles

    - by Chris Henry
    When building objects that make use of data stored in a RDBMS, it's normally pretty clear what you're getting back, as dictated by the tables and columns being queried. However, when dealing with NoSQL, document-based systems, it's less clear what is being retrieved. What are common methods of keeping track of structure in which data is stored?

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  • Saving Data to Relational Database (Entity Framework)

    - by sheefy
    I'm having a little bit of trouble saving data to a database. Basically, I have a main table that has associations to other tables (Example Below). Tbl_Listing ID UserID - Associated to ID in User Table CategoryID - Associated to ID in Category Table LevelID - Associated to ID in Level Table. Name Address Normally, it's easy for me to add data to the DB (using Entity Framework). However, I'm not sure how to add data to the fields with associations. The numerous ID fields just need to hold an int value that corresponds with the ID in the associated table. For example; when I try to access the column in the following manner I get a "Object reference not set to an instance of an object." error. Listing NewListing = new Listing(); NewListing.Tbl_User.ID = 1; NewListing.Tbl_Category.ID = 2; ... DBEntities.AddToListingSet(NewListing); DBEntities.SaveChanges(); I am using NewListing.Tbl_User.ID instead of NewListing.UserID because the UserID field is not available through intellisense. If I try and create an object for each related field I get a "The relationship between the two objects cannot be defined because they are attached to different ObjectContext objects." error. With this method, I am trying to add the object without the .ID shown above - example NewListing.User = UserObject. I know this should be simple as I just want to reference the ID from the associated table in the main Listing's table. Any help would be greatly appreciated. Thanks in advance, -S

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  • System of linear equations in C++?

    - by Archagon
    I need to solve a system of linear equations in my program. Is there a simple linear algebra library for C++, preferably comprised of no more than a few headers? I've been looking for nearly an hour, and all the ones I found require messing around with Linux, compiling DLLs in MinGW, etc. etc. etc. (I'm using Visual Studio 2008.)

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  • Moving webshop storage to NoSQL solution

    - by mare
    If you had a webshop solution based on SQL Server relational DB what would be the reasons, if any, to move to NoSQL storage ? Does it even make sense to migrate datastores that rely on relations heavily to NoSQL? If starting from scratch, would you choose NoSQL solution over relational one for a webshop project, which will, after a while, again end up with a bunch of tables like Articles, Classifications, TaxRates, Pricelists etc. and a magnitude of relations between them? What's the support like in .NET (4.0) for MongoDB or MongoDB's support for .NET 4.0? Can I count on rich code generation tools similar to EF wizard, L2SQL wizard etc. for MongoDB? Because as what I have read so far, NoSQL's are mostly suited for document storage, simpler object models. Your answer to this question will help me make the right infrastructure design decisions.

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  • Efficient 4x4 matrix inverse (affine transform)

    - by Budric
    Hi, I was hoping someone can point out an efficient formula for 4x4 affine matrix transform. Currently my code uses cofactor expansion and it allocates a temporary array for each cofactor. It's easy to read, but it's slower than it should be. Note, this isn't homework and I know how to work it out manually using 4x4 co-factor expansion, it's just a pain and not really an interesting problem for me. Also I've googled and came up with a few sites that give you the formula already (http://www.euclideanspace.com/maths/algebra/matrix/functions/inverse/fourD/index.htm). However this one could probably be optimized further by pre-computing some of the products. I'm sure someone came up with the "best" formula for this at one point or another? Thanks.

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  • subscript for a join (\bowtie) operation in LyX/LaTeX

    - by Amir Rachum
    I'm using LyX to write some Relational Algebra queries. I'm using the \bowtie symbol for the join operation but when I try to put a text in subscript directly under the symbol, I get the following error: ...a_{\t{pId}}\t{person}\right)\bowtie\limits {\t{pId}{1}=\t{pId}_{2}... I'm ignoring this misplaced \limits or \nolimits command. Anyone knows how to do what I want? Preferably in LyX, but ERT code snippets will also be appreciated. Thanks! Edit: \t is a macro for \text.

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  • This is more a matlab/math brain teaser than a question

    - by gd047
    Here is the setup. No assumptions for the values I am using. n=2; % dimension of vectors x and (square) matrix P r=2; % number of x vectors and P matrices x1 = [3;5] x2 = [9;6] x = cat(2,x1,x2) P1 = [6,11;15,-1] P2 = [2,21;-2,3] P(:,1)=P1(:) P(:,2)=P2(:) modePr = [-.4;16] TransPr=[5.9,0.1;20.2,-4.8] pred_modePr = TransPr'*modePr MixPr = TransPr.*(modePr*(pred_modePr.^(-1))') x0 = x*MixPr Then it was time to apply the following formula to get myP , where µij is MixPr. I used this code to get it: myP=zeros(n*n,r); Ptables(:,:,1)=P1; Ptables(:,:,2)=P2; for j=1:r for i = 1:r; temp = MixPr(i,j)*(Ptables(:,:,i) + ... (x(:,i)-x0(:,j))*(x(:,i)-x0(:,j))'); myP(:,j)= myP(:,j) + temp(:); end end Some brilliant guy proposed this formula as another way to produce myP for j=1:r xk1=x(:,j); PP=xk1*xk1'; PP0(:,j)=PP(:); xk1=x0(:,j); PP=xk1*xk1'; PP1(:,j)=PP(:); end myP = (P+PP0)*MixPr-PP1 I tried to formulate the equality between the two methods and seems to be this one. To make things easier, I ignored from both methods the summation of matrix P. where the first part denotes the formula that I used, while the second comes from his code snippet. Do you think this is an obvious equality? If yes, ignore all the above and just try to explain why. I could only start from the LHS, and after some algebra I think I proved it equals to the RHS. However I can't see how did he (or she) think of it in the first place.

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  • The Next-gen Databases

    - by Randin
    I'm learning traditional Relational Databases (with PostgreSQL) and doing some research I've come across some new types of databases. CouchDB, Drizzle, and Scalaris to name a few, what is going to be the next database technologies to deal with?

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  • Database design -- does it respect 3rd NF?

    - by Flavius
    Hi I have the following relations (tables) in a relational model Person person_id, first_name, last_name, address Student person_id, matr_nr Teacher person_id, salary Lecture lecture_id, lect_name, lect_description Attendees lecture_id, person_id, date I'm wondering about the functional dependencies of Student and Teacher. Do these tables respect the 3rd normal form? Which should be the primary keys of these tables?

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  • How can an SQL relational database be used to model a thesaurus? [closed]

    - by Miles O'Keefe
    I would like to design a web app that functions as a simple thesaurus: a long list of words with attributes, all of which are linked to each other. This thesaurus data model can be defined as: a controlled vocabulary arranged in a known order in which equivalence, hierarchical, and associative relationships among terms are clearly displayed and identified by standardized relationship indicators. My idea so far is to have one database in which every word is a table, and every table contains all words related to that word. e.g. Thesaurus(database) - happy(table) - excited(row)|cheerful(row)|lively(row) Is there are more efficient way to store words and their relationship to other words in a relational SQL database?

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  • Which of the following relational database management systems would a company adopt (for migration), if any, MS Access, MS SQL Server or MySQL?

    - by Hassan Hagi
    Dear programmers, as part of my final year university project, I am conducting research into relational database management systems such as Microsoft Office Access 2007, Microsoft SQL Server 2008 and MySQL 5.1. The description does not need to be detailed however; I am trying to find empirical evidence and professional opinion/fact to determine which of the three databases are best suited for the required size of company (stated or unstated). OS: Microsoft windows (XP or newer) Please consider the following, but full details are not necessary: Memory management Migration Design constraints Integrity (data and others) Triggers User constraints Ease of use Performance Crash Recovery (not the operating system) Total Cost of Ownership (TCO) Also any info on Open source (to do with the three RDBMS) Thank you for your time and help. Hassan Hagi

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  • Building dynamic OLAP data marts on-the-fly

    - by DrJohn
    At the forthcoming SQLBits conference, I will be presenting a session on how to dynamically build an OLAP data mart on-the-fly. This blog entry is intended to clarify exactly what I mean by an OLAP data mart, why you may need to build them on-the-fly and finally outline the steps needed to build them dynamically. In subsequent blog entries, I will present exactly how to implement some of the techniques involved. What is an OLAP data mart? In data warehousing parlance, a data mart is a subset of the overall corporate data provided to business users to meet specific business needs. Of course, the term does not specify the technology involved, so I coined the term "OLAP data mart" to identify a subset of data which is delivered in the form of an OLAP cube which may be accompanied by the relational database upon which it was built. To clarify, the relational database is specifically create and loaded with the subset of data and then the OLAP cube is built and processed to make the data available to the end-users via standard OLAP client tools. Why build OLAP data marts? Market research companies sell data to their clients to make money. To gain competitive advantage, market research providers like to "add value" to their data by providing systems that enhance analytics, thereby allowing clients to make best use of the data. As such, OLAP cubes have become a standard way of delivering added value to clients. They can be built on-the-fly to hold specific data sets and meet particular needs and then hosted on a secure intranet site for remote access, or shipped to clients' own infrastructure for hosting. Even better, they support a wide range of different tools for analytical purposes, including the ever popular Microsoft Excel. Extension Attributes: The Challenge One of the key challenges in building multiple OLAP data marts based on the same 'template' is handling extension attributes. These are attributes that meet the client's specific reporting needs, but do not form part of the standard template. Now clearly, these extension attributes have to come into the system via additional files and ultimately be added to relational tables so they can end up in the OLAP cube. However, processing these files and filling dynamically altered tables with SSIS is a challenge as SSIS packages tend to break as soon as the database schema changes. There are two approaches to this: (1) dynamically build an SSIS package in memory to match the new database schema using C#, or (2) have the extension attributes provided as name/value pairs so the file's schema does not change and can easily be loaded using SSIS. The problem with the first approach is the complexity of writing an awful lot of complex C# code. The problem of the second approach is that name/value pairs are useless to an OLAP cube; so they have to be pivoted back into a proper relational table somewhere in the data load process WITHOUT breaking SSIS. How this can be done will be part of future blog entry. What is involved in building an OLAP data mart? There are a great many steps involved in building OLAP data marts on-the-fly. The key point is that all the steps must be automated to allow for the production of multiple OLAP data marts per day (i.e. many thousands, each with its own specific data set and attributes). Now most of these steps have a great deal in common with standard data warehouse practices. The key difference is that the databases are all built to order. The only permanent database is the metadata database (shown in orange) which holds all the metadata needed to build everything else (i.e. client orders, configuration information, connection strings, client specific requirements and attributes etc.). The staging database (shown in red) has a short life: it is built, populated and then ripped down as soon as the OLAP Data Mart has been populated. In the diagram below, the OLAP data mart comprises the two blue components: the Data Mart which is a relational database and the OLAP Cube which is an OLAP database implemented using Microsoft Analysis Services (SSAS). The client may receive just the OLAP cube or both components together depending on their reporting requirements.  So, in broad terms the steps required to fulfil a client order are as follows: Step 1: Prepare metadata Create a set of database names unique to the client's order Modify all package connection strings to be used by SSIS to point to new databases and file locations. Step 2: Create relational databases Create the staging and data mart relational databases using dynamic SQL and set the database recovery mode to SIMPLE as we do not need the overhead of logging anything Execute SQL scripts to build all database objects (tables, views, functions and stored procedures) in the two databases Step 3: Load staging database Use SSIS to load all data files into the staging database in a parallel operation Load extension files containing name/value pairs. These will provide client-specific attributes in the OLAP cube. Step 4: Load data mart relational database Load the data from staging into the data mart relational database, again in parallel where possible Allocate surrogate keys and use SSIS to perform surrogate key lookup during the load of fact tables Step 5: Load extension tables & attributes Pivot the extension attributes from their native name/value pairs into proper relational tables Add the extension attributes to the views used by OLAP cube Step 6: Deploy & Process OLAP cube Deploy the OLAP database directly to the server using a C# script task in SSIS Modify the connection string used by the OLAP cube to point to the data mart relational database Modify the cube structure to add the extension attributes to both the data source view and the relevant dimensions Remove any standard attributes that not required Process the OLAP cube Step 7: Backup and drop databases Drop staging database as it is no longer required Backup data mart relational and OLAP database and ship these to the client's infrastructure Drop data mart relational and OLAP database from the build server Mark order complete Start processing the next order, ad infinitum. So my future blog posts and my forthcoming session at the SQLBits conference will all focus on some of the more interesting aspects of building OLAP data marts on-the-fly such as handling the load of extension attributes and how to dynamically alter the structure of an OLAP cube using C#.

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  • Object mapping in objective-c (iphone) from JSON

    - by freshfunk
    For my iPhone app, I'm consuming a RESTful service and getting JSON. I've found libraries to deserialize this into an NSDictionary. However, I'm wondering if there are any libraries to deserialize the JSON/NSDictionary/Property List into my object (an arbitrary one on my side). The java equivalent would be the object-relational mappers although the sort of object mapping I'm looking for is relatively straightforward (simple data types, no complex relationships, etc.). I noticed that Objective-C does have introspection so it seems theoretically possible but I haven't found a library to do it. Or is there a simple way to load an object from an NSDictionary/Property List object that doesn't require modification every time the object changes? For example: { "id" : "user1", "name" : "mister foobar" "age" : 20 } gets loaded into object @interface User : NSObject { NSString *id; NSString *name; int *age; }

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  • Query for props list with or without values

    - by vitto
    Hi, I'm trying to make a SELECT on three relational tables like these ones: table_materials -> material_id - material_name table_props -> prop_id - prop_name table_materials_props - row_id -> material_id -> prop_id - prop_value On my page, I'd like to get a result like this one but i have some problem with the query: material prop A prop B prop C prop D prop E wood 350 NULL NULL 84 16 iron NULL 17 NULL NULL 201 copper 548 285 99 NULL NULL so the query should return something like: material prop_name prop_value wood prop A 350 wood prop B NULL wood prop C NULL wood prop D 84 wood prop E 16 // and go on with others rows i thought to use something like: SELECT * FROM table_materials AS m INNER JOIN table_materials_props AS mp ON m.material_id = mp.material_id INNER JOIN table_materials_props AS p ON mp.prop_id = p.prop_id ORDER BY p.prop_name the problem is the query doesn't return the NULL values, and I need the same prop order for all the materials regardless of prop values are NULL or not I hope this example is clear!

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  • Using nodereference + views to create combined view

    - by Ian Silber
    I'm trying to set up a relational View but not sure how to do it. Here's an example of what I'm going for using the node types Artist and Song. Artist Song Length Bob Dylan Like a Rolling Stone 2:00 Bruce Springsteen Atlantic City 4:00 Burce Springsteen Born to Run 5:24 Van Morrison Domino 3:22 Van Morrison Brown Eyed Girl 4:30 Assuming I have an Artist node type that has a node reference to Song (set to unlimited) and a Song data type with an additional field for length, how would I go about configuring the view to output this view? Thanks! Ian

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  • Question about OOP and objects.

    - by loddn
    I have a school assignment, a Dog Show. My assignment is to create a website where vistors can display results and Judges and Secretary can admin, crud. I have a small problem one part of the assignment. The result should be based on two protokols from different judges and after that checked by the secretary before the result is displayed for the user. I have to say i'm fairly new to programming and so i need some smart suggestions on how to design and implement this. The assignment should cover both a db and c# (.net mvc). Q1: How do i create a object (result)that depends on two other objects(protocol)? Is that even needed? Q2: How to solve this in a relational db?

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  • Best way to model Customer <--> Address

    - by Jen
    Every Customer has a physical address and an optional mailing address. What is your preferred way to model this? Option 1. Customer has foreign key to Address Customer (id, phys_address_id, mail_address_id) Address (id, street, city, etc.) Option 2. Customer has one-to-many relationship to Address, which contains a field to describe the address type Customer (id) Address (id, customer_id, address_type, street, city, etc.) Option 3. Address information is de-normalized and stored in Customer Customer (id, phys_street, phys_city, etc. mail_street, mail_city, etc.) One of my overriding goals is to simplify the object-relational mappings, so I'm leaning towards the first approach. What are your thoughts?

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  • How to organise a many to many relationship in MongoDB

    - by Gareth Elms
    I have two tables/collections; Users and Groups. A user can be a member of any number of groups and a user can also be an owner of any number of groups. In a relational database I'd probably have a third table called UserGroups with a UserID column, a GroupID column and an IsOwner column. I'm using MongoDB and I'm sure there is a different approach for this kind of relationship in a document database. Should I embed the list of groups and groups-as-owner inside the Users table as two arrays of ObjectIDs? Should I also store the list of members and owners in the Groups table as two arrays, effectively mirroring the relationship causing a duplication of relationship information? Or is a bridging UserGroups table a legitimate concept in document databases for many to many relationships? Thanks

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  • How can I copy a SQL record which has related records in other tables to the same database?

    - by DerekVS
    Hi. I created a function in C# which allows me to copy a record and its related children to a new record and new related children in the same database. (This is for an application that allows the use of previous work as a template for new work.) Anyway, it works great... Here's a description of how it accomplishes the copy: It populates a two-column memory-based look-up table with the current primary key of each record. Next, as it individually creates each new copy record, it updates the look-up table with the Identity PK of the new record [retrieved from SCOPE_IDENTITY()]. Now, when it copies over any related children, it can look up the new parent PK to set the FK on the new record. In testing, it only took a minute to copy a relational structure on a local instance of SQL Server 2005 Express Edition. Unfortunately it is proving to be horribly slow in production! My users are dealing with 60,000+ records per parent record over the LAN to our SQL Server! While my copy function still works, each of those records represents an individual SQL UPDATE command and it loads the SQL Server at about 17% CPU from its normal 2% idle. I just finished testing a 50,000 record copy and it took almost 20 minutes! Is there a way to duplicate this functionality in SQL queries or stored procecures to make the SQL server do all of the copy work instead of blasting it over the LAN from each client? (We're running Microsoft SQL Server 2005 Standard Edition.) Thanks! -Derek

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  • Modeling a Generic Relationship in a Database

    - by StevenH
    This is most likely one for all you sexy DBAs out there: How would I effieciently model a relational database whereby I have a field in an "Event" table which defines a "SportType". This "SportsType" field can hold a link to different sports tables E.g. "FootballEvent", "RubgyEvent", "CricketEvent" and "F1 Event". Each of these Sports tables have different fields specific to that sport. My goal is to be able to genericly add sports types in the future as required, yet hold sport specific event data (fields) as part of my Event Entity. Is it possible to use an ORM such as NHibernate / Entity framework which would reflect such a relationship? I have thrown together a quick C# example to express my intent at a higher level: public class Event<T> where T : new() { public T Fields { get; set; } public Event() { EventType = new T(); } } public class FootballEvent { public Team CompetitorA { get; set; } public Team CompetitorB { get; set; } } public class TennisEvent { public Player CompetitorA { get; set; } public Player CompetitorB { get; set; } } public class F1RacingEvent { public List<Player> Drivers { get; set; } public List<Team> Teams { get; set; } } public class Team { public IEnumerable<Player> Squad { get; set; } } public class Player { public string Name { get; set; } public DateTime DOB { get; set;} }

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  • How should I manage my many-to-many relationships?

    - by wes
    Hello all, I have a database containing a couple tables: files and users. This relationship is many-to-many, so I also have a table called users_files_ref which holds foreign keys to both of the above tables. Here's the schema of each table: files - file_id, file_name users - user_id, user_name users_files_ref - user_file_ref_id, user_id, file_id I'm using Codeigniter to build a file host application, and I'm right in the middle of adding the functionality that enables users to upload files. This is where I'm running into my problem. Once I add a file to the files table, I will need that new file's id to update the users_files_ref table. Right now I'm adding the record to the files table, and then I imagined I'd run a query to grab the last file added, so that I can get the ID, and then use that ID to insert the new users_files_ref record. I know this will work on a small scale, but I imagine there is a better way of managing these records, especially in a heavy-traffic scenario. I am new to relational database stuff but have been around PHP for a while, so please bear with me here :-) I have primary and foreign keys set up correctly for the files, users, and users_files_ref tables, I'm just wondering how to manage the adding of file records for this scenario? Thanks for any help provided, it's much appreciated. -Wes

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  • Modeling a Generic Relationship (expressed in C#) in a Database

    - by StevenH
    This is most likely one for all you sexy DBAs out there: How would I effieciently model a relational database whereby I have a field in an "Event" table which defines a "SportType"? This "SportsType" field can hold a link to different sports tables E.g. "FootballEvent", "RubgyEvent", "CricketEvent" and "F1 Event". Each of these Sports tables have different fields specific to that sport. My goal is to be able to genericly add sports types in the future as required, yet hold sport specific event data (fields) as part of my Event Entity. Is it possible to use an ORM such as NHibernate / Entity framework / DataObjects.NET which would reflect such a relationship? I have thrown together a quick C# example to express my intent at a higher level: public class Event<T> where T : new() { public T Fields { get; set; } public Event() { EventType = new T(); } } public class FootballEvent { public Team CompetitorA { get; set; } public Team CompetitorB { get; set; } } public class TennisEvent { public Player CompetitorA { get; set; } public Player CompetitorB { get; set; } } public class F1RacingEvent { public List<Player> Drivers { get; set; } public List<Team> Teams { get; set; } } public class Team { public IEnumerable<Player> Squad { get; set; } } public class Player { public string Name { get; set; } public DateTime DOB { get; set;} }

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