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  • What advantages do we have when creating a separate mapping table for two relational tables

    - by Pankaj Upadhyay
    In various open source CMS, I have noticed that there is a separate table for mapping two relational tables. Like for categories and products, there is a separate product_category_mapping table. This table just has a primary key and two foreign keys from the categories and product tables. My question is what are the benefits of this database design rather than just linking the tables directly by defining a foreign key in either table? Is it just matter of convenience?

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  • Going Beyond the Relational Model with Data

    SQL is a powerful tool for querying data, and for aggregating it. However, you can't easily use it to draw inferences, to make predictions, or to tease out subtle correlations. To provide ever more sophisticated inferences to businesses, the race is on to combine the power of the relational model with advanced statistical packages. Both IBM and PostGres are ready with solutions. And SQL Server? Hmm...

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  • Prove that the set of regular languages is a proper subset of the set of the context-free languages

    - by David Relihan
    I was brushing up (not homework)on some computation-theory and came accross this problem: How can you prove that the set of regular languages is a proper subset of the set of the context-free languages. Now I know a language is regular iff it is accepted by a finite automaton. And I know a language is context-free iff it is accepted by a pushdown automaton. But I'm not sure of what solution is.

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  • structure problem in Relational DBMS creation

    - by Kane
    For learning and understanding purpose, I currently want to try to make a small relational DBMS with simple features like (for now) only sequential reading/writing and CREATE TABLE, INSERT, SELECT, UPDATE and DELETE management. I am currently on the "think" part of the project and I am stuck on the way to store the read data in memory. First I was thinking of putting them properly on a structure, but the problem is that tables are all different, know the type of each column is not an issue, but I am not sure C provide a way to make fully dynamic structure. My second and current idea is to make a simple char array of the required length and just get the data by order with cast. But I am not sure if it is the good way to do that part, so I wanted to ask for your opinion and advices about that. Thanks in advance for your help. nb: I hope my question is enough clear and understandable, I still lack of pratice in english

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  • Sets, Surrogates, Normalisation, Referential Integrity - the Theory with example Scaling considerati

    - by tonyrogerson
    The Slides and Demo's for the SQLBits session I did today at SQL Bits in London are attached. The Agenda was... Thinking in Sets Surrogate Keys ú What they are ú Comparison NEWID, NEWSEQUENTIALID, IDENTITY ú Fragmenation Normalisation ú An introduction – what is it? Why use it? ú Joins – Pre-filter problems, index intersection ú Fragmentation again Referential Integrity ú Optimiser -> Query rewrite ú Locking considerations around Foreign Keys and Declarative RI (using Triggers)...(read more)

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  • The Grand Unified Framework Theory

    Tom Janssens left a comment: What still bugs me is that we do not have a unified pattern for all .net dev (using modelbinders and icommand for example...) But, Tom we are pretty close. At least as close as we should be, I think. With .NET there are plenty of low level patterns we can reuse regardless of the application platform or architecture. Stuff like: Asynchronous programming with events or the TPL. Object queries with LINQ. Resource management with IDispose. At a higher...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • PageRank is the Best Indicator of Competition Strength For a Keyword in SEO - New Verifiable Theory

    The major argument against PageRank in SEO is that pages with zero PageRank can be in the top positions even for highly competitive keywords. However, we are left with requiring an explanation as to why "PageRank is Google's view of the importance of this page." It becomes apparent that either Google is misleading us or we have all been misinterpreting Google's statement. From extensive evaluation of the top Google search engine results pages for hundreds of keywords, the author observed that those high positioned web pages with PageRanks of zero have a home page with higher PageRanks, usually three or more.

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  • Actually utilizing relational databases for entity systems

    - by Marc Müller
    Recently I was researching several entity systems and obviously I came across T=Machine's fantastic articles on the subject. In Part 5 of the series the author uses a relational schema to explain how an entity system is built and works. Since reading this, I have been wondering whether or not actually using a compact SQL library would be fast enough for real-time usage in video games. Performance seems to be the main issue with a full blown SQL database for management of all entities and components. However, as mentioned in T=Machine's post, basically all access to data inside the SQLDB is done sequentlially by each system over each component. Additionally, using a library like SQLite, one could easily improve performance by storing the entity data exclusively in RAM to increase access speeds. Disregarding possible performance issues, using a SQL database, in my opinion, would allow for a very intuitive implementation of entity systems and bring a long certain other benefits like easy de/serialization of game states and consistency checks like the uniqueness of entity IDs. Edit for clarification: The main question was whether using a SQL database for the actual entity management (not just storing the game state on the disk) in a real-time game would still yield a framerate appropriate for a game or even if someone is aware of projects that demonstrate SQL in a video game.

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  • 2-D Lighting Theory

    - by Richard
    I am writing a rogue-like 'zombie' management game. The game map will be similar to Prison Architect. A top-down 50 X 50 grid. I want to implemented a day night cycle and during the night I would like the player to be able to position lights. I would like to be able to lighten and dark to whole map to display the day and night cycle. Then lights would be a circle of light blocked by game entities such as walls, players, trees etc. How would I achieve and what is the standard way of achieving this?

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  • What is the best database for my needs?

    - by Mr. Flibble
    I am currently using MS SQL Server 2008 but I'm not sure it it is the best system for this particular task. I have a single table like so: PK_ptA PK_ptB DateInserted LookupColA LookupColB ... LookupColF DataCol (ntext) A common query is SELECT TOP(1000000) DataCol FROM table WHERE LookupColA=x AND LookupColD=y AND LookupColE=z ORDER BY DateInserted DESC The table has about a billion rows with 5 million inserted per day. My main problem with SQL Server is that it isn't too easy to shard or spread out the datafiles. Also, exporting seems to max out at 1000rows per second (about 1MB/s) which seems very slow. Another problem I have is, with SQL Server, if I want to add a new LookupCol the log file grows enormously requiring a large amount of rarely used free space on tap. Are there any obvious better solutions for this problem?

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  • Non-Relational Database Design

    - by Ian Varley
    I'm interested in hearing about design strategies you have used with non-relational "nosql" databases - that is, the (mostly new) class of data stores that don't use traditional relational design or SQL (such as Hypertable, CouchDB, SimpleDB, Google App Engine datastore, Voldemort, Cassandra, SQL Data Services, etc.). They're also often referred to as "key/value stores", and at base they act like giant distributed persistent hash tables. Specifically, I want to learn about the differences in conceptual data design with these new databases. What's easier, what's harder, what can't be done at all? Have you come up with alternate designs that work much better in the non-relational world? Have you hit your head against anything that seems impossible? Have you bridged the gap with any design patterns, e.g. to translate from one to the other? Do you even do explicit data models at all now (e.g. in UML) or have you chucked them entirely in favor of semi-structured / document-oriented data blobs? Do you miss any of the major extra services that RDBMSes provide, like relational integrity, arbitrarily complex transaction support, triggers, etc? I come from a SQL relational DB background, so normalization is in my blood. That said, I get the advantages of non-relational databases for simplicity and scaling, and my gut tells me that there has to be a richer overlap of design capabilities. What have you done? FYI, there have been StackOverflow discussions on similar topics here: the next generation of databases changing schemas to work with Google App Engine choosing a document-oriented database

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  • Entity framework (1): implement 1 foreign key to multiple tables

    - by Michel
    Hi, i've modeled this: i have an import table, and an import steps table import 1 .. N importsteps Now i have a table importparams, which hold key/value pairs to register all kind of info about the import or the importsteps. So i have modeled a FK in SqlServer which points to the PK of the import table and to the PK of the importsteps table (the ID's for both the import as the importsteps table are guids, so i can query the importparams with either the id from import or from importsteps and get the right importparams). Makes sense a bit? But how can i model this in the EF? I can see it's a bit hard for the EF to model this, because one realtion can point to multiple classes, but is there a way? The workaround normally is just to get all importparams where FK is the ID, but as you know the FK is not available in the EF version 1. I hope you can help me out, michel

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  • Context Free Language Question (Pumping Lemma)

    - by Maixy
    I know this isn't directly related to programming, but I was wondering if anyone know how to apply the pumping lemma to the following proof: Show that L={(a^n)(b^n)(c^m) : n!=m} is not a context free language I'm pretty confident with applying pumping lemmas, but this one is really irking me. What do you think?

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  • Convert a post-order binary tree traversal index to an level-order (breadth-first) index

    - by strfry
    Assuming a complete binary tree, each node can be adressed with the position it appears in a given tree traversal algorithm. For example, the node indices of a simple complete tree with height 3 would look like this: breadth first (aka level-order): 0 / \ 1 2 / \ / \ 3 4 5 6 post-order dept first: 6 / \ 2 5 / \ / \ 0 1 3 4 The height of the tree and an index in the post-order traversal is given. How can i calculate the breadth first index from this information?

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  • Is there an ORM with APIs to be used programatically?

    - by Kabeer
    Hello. Neither did not get any response for my previous question, nor enough views :) So here I am now framing my query afresh. Is there any ORM that offers APIs to be used programatically? In my situation, a user will be helped through a wizard to define some entities. Thereafter those entites will be created in a database in form of tables (there will of course be some improvization). I need an ORM that offers APIs for modeling and creating entities during application runtime and not just during design time. Mine is a .Net application, therefore I was looking at Entity Framework. However, to me it looked tied to Visual Studio (I may be wrong also as I am new to it). Any recommendations? Or alternative point of view?

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  • What db fits me?

    - by afvasd
    Dear Everyone I am currently using mysql. I am finding that my schema is getting incredibly complicated. I seek to find a new db that will suit my needs: Let's assume I am building a news aggregrator (which collects news from multiple website). I then run algorithms to determine if two news from different sites are actually referring to the same topic. I run this algorithm to cluster news together. The relationship is depicted below: cluster \--news1 \--word1 \--word2 \--news2 \--word3 \--news3 \--word1 \--word3 And then I will apply some magic and determine the importance of each word. Summing all the importance of each word gives me the importance of a news article. Summing the importance of each news article gives me the importance of a cluster. Note that above cluster there are also subgroups( like split by region etc), and categories (like sports, etc) which I have to determine the importance of that in a particular day per se. I have used views in the past to do so, but I realized that views are very slow. So i will normally do an insert into an actual table and index them for better performance. As you can see this leads to multiple tables derived like (cluster, importance), (news, importance), (words, importance) etc which can get pretty messy. Also the "importance" metric will change. It has become increasingly difficult to alter tables, update data (which I am using TRUNCATE TABLE) and then inserting from null. I am currently looking into something schemaless like Mongodb. I do not need distributedness. I would very much want something that is reasonably fast (which can be indexed) and something that is a lot more flexible that traditional RDMBS. Also, I need something that has some kind of ORM because I personally like ORM a lot. I am currently using sqlalchemy Please help!

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  • Graph Theory: How to compute closeness centrality for each node in a set of data?

    - by Jordan
    I'd like to learn how to apply network theory to my own cache of relational data. I'm trying to build a demo of a new way of browsing a music library, using network theory, that I think would make for a very intuitive and useful way of finding the right song at any given time. I have all the data (artists as nodes, similarity from 0 to 1 between each artist and those it is related to) and I can already program, but I don't know how to actually calculate the centrality of a node from that. I've spent a while trying to email different professors at my school but no one seems to know where I can learn this. I hope someone's done something similar. Thanks in advance you guys! ~Jordan

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  • Online Introduction to Relational Databases (and not only) with Stanford University!

    - by Luca Zavarella
    How many of you know exactly the definition of "relational database"? What exactly the adjective "relational" refers to? Many of you allow themselves to be deceived, thinking this adjective is related to foreign key constraints between tables. Instead this adjective lurks in a world based on set theory, relational algebra and the concept of relationship intended as a table.Well, for those who want to deep the fundamentals of relational model, relational algebra, XML, OLAP and emerging "NoSQL" systems, Stanford University School of Engineering offers a public and free online introductory course to databases. This is the related web page: http://www.db-class.com/ The course will last 2 months, after which there will be a final exam. Passing the final exam will entitle the participants to receive a statement of accomplishment. A syllabus and more information is available here. Happy eLearning to you!

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  • SQL SERVER Enumerations in Relational Database Best Practice

    This article has been submitted by Marko Parkkola, Data systems designer at Saarionen Oy, Finland. Marko is excellent developer and always thinking at next level. You can read his earlier comment which created very interesting discussion here: SQL SERVER- IF EXISTS(Select null from table) vs IF EXISTS(Select 1 from table). I must express my special [...]...Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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  • Extracting the Layout of all the Data Forms from the Relational Database

    - by RahulS
    Today I came across a question from one of our clients that: "what members are used on each data form WITHOUT having to go through the report generated out of our Planning app". We worked with client on this and reached to a simple query. All the form related information is stored in the following tables: HSP_FORM HSP_FORMOBJ_DEF HSP_FORMOBJ_DEF_MBR HSP_FORM_ATTRIBUTES HSP_FORM_CALCS HSP_FORM_DV_CONDITION HSP_FORM_DV_PM_RULE HSP_FORM_DV_RULE HSP_FORM_DV_USER_IN_PM_RULE HSP_FORM_LAYOUT HSP_FORM_MENUS HSP_FORM_VARIABLES If we want to retrieve just the members included, we can concentrate on: HSP_OBJECT to get the Object_ID for form, Object_Type is 7 for forms. (Ex: Select * from HSP_OBJECT where OBJECT_TYPE = 7) HSP_FORMOBJ_DEF Find the OBJDEF_ID for a particular form HSP_FORMOBJ_DEF_MBR Use the above OBJDEF_ID to find the members: Here the Mbr_ID is the Id of the member and Query_Type is the Function like Idesc, Level0 etc and Sequce is you sequence, And the final table we can use is HSP_FORM_LAYOUT: Layout_Type: 0->Pov 1-> Page, 2->Row, 3->Col, DIM_ID is the dimension ID and Ordinal is position. Here is the Query: SELECT HSP_OBJECT.OBJECT_NAME AS 'Form',  HSP_OBJECT_2.OBJECT_NAME AS 'Dimension',  HSP_OBJECT_1.OBJECT_NAME AS 'Member',  HSP_FORMOBJ_DEF_MBR.QUERY_TYPE FROM  <DatabaseName>.dbo.HSP_FORM_LAYOUT HSP_FORM_LAYOUT,  <DatabaseName>.dbo.HSP_FORMOBJ_DEF HSP_FORMOBJ_DEF,  <DatabaseName>.dbo.HSP_FORMOBJ_DEF_MBR HSP_FORMOBJ_DEF_MBR,  <DatabaseName>.dbo.HSP_MEMBER HSP_MEMBER,  <DatabaseName>.dbo.HSP_OBJECT HSP_OBJECT,  <DatabaseName>.dbo.HSP_OBJECT HSP_OBJECT_1,  <DatabaseName>.dbo.HSP_OBJECT HSP_OBJECT_2 WHERE  HSP_OBJECT.OBJECT_ID = HSP_FORMOBJ_DEF.FORM_ID AND  HSP_FORMOBJ_DEF_MBR.OBJDEF_ID = HSP_FORMOBJ_DEF.OBJDEF_ID AND  HSP_MEMBER.MEMBER_ID = HSP_FORMOBJ_DEF_MBR.MBR_ID AND  HSP_OBJECT_1.OBJECT_ID = HSP_MEMBER.MEMBER_ID AND  HSP_OBJECT_2.OBJECT_ID = HSP_MEMBER.DIM_ID AND  HSP_FORM_LAYOUT.DIM_ID = HSP_MEMBER.DIM_ID AND  HSP_FORM_LAYOUT.FORM_ID = HSP_FORMOBJ_DEF.FORM_ID AND  ((HSP_OBJECT.OBJECT_TYPE=7)) ORDER BY HSP_OBJECT.OBJECT_NAME  Concentrate on Test1 data form and Actual Layout of it as follows: Corresponding Query_type for few of the functions: 9  for Idesc, 3  for Ancestors, -9 for ILvl0Des, 8  for Desc, 4  for IAncestors Its just a basic idea you can do lot on the basis of this. Cheers..!!! Rahul S. http://www.facebook.com/pages/HyperionPlanning/117320818374228

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