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  • Optimize SUMMARIZE with ADDCOLUMNS in Dax #ssas #tabular #dax #powerpivot

    - by Marco Russo (SQLBI)
    If you started using DAX as a query language, you might have encountered some performance issues by using SUMMARIZE. The problem is related to the calculation you put in the SUMMARIZE, by adding what are called extension columns, which compute their value within a filter context defined by the rows considered in the group that the SUMMARIZE uses to produce each row in the output. Most of the time, for simple table expressions used in the first parameter of SUMMARIZE, you can optimize performance by removing the extended columns from the SUMMARIZE and adding them by using an ADDCOLUMNS function. In practice, instead of writing SUMMARIZE( <table>, <group_by_column>, <column_name>, <expression> ) you can write: ADDCOLUMNS(     SUMMARIZE( <table>, <group by column> ),     <column_name>, CALCULATE( <expression> ) ) The performance difference might be huge (orders of magnitude) but this optimization might produce a different semantic and in these cases it should not be used. A longer discussion of this topic is included in my Best Practices Using SUMMARIZE and ADDCOLUMNS article on SQLBI, which also include several details about the DAX syntax with extended columns. For example, did you know that you can create an extended column in SUMMARIZE and ADDCOLUMNS with the same name of existing measures? It is *not* a good thing to do, and by reading the article you will discover why. Enjoy DAX!

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  • Is there any open source code analyzer for java which I can adopt my software metrics algorithm on it?

    - by daneshkohan
    I am doing my masters dissertation and I have conducted a software metrics. I need to adopt my metrics on an open source tool. I have found PMD and check style on sourceforge.net but there is not adequate explanation about their codes. However, I couldn't to find their source code to customize them. I will be appreciated, if you introduce one open source tool for java which I can customize it's code.

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  • Implement Budget Allocation in DAX for Power Pivot and Tabular #powerpivot #tabular #ssas #dax

    - by Marco Russo (SQLBI)
    Comparing sales and budget, or costs and budget, is a very common operation. However, it is often the case that you have different granularities for different tables containing budget and the data to compare with. There are two ways to do that: you can limit the comparison to the granularity that is common to the two tables, or you can allocate the budget where it’s not defined. For example, if you have a budget defined by quarter and category, you might want to allocate it by month and product. In this way, you will do the comparison as you had a more granular definition of the budget, without actually having to do the manual job of allocating data (usually in an Excel worksheet!). If you want to do budget allocation in DAX, you can use the Budget Patterns we published on DAX Patterns. If you come from and MDX/OLAP background, at first you might find it hard to solve the problem of not having attribute hierarchies that helps you in propagating the budget values to lower hierarchical levels. However, I think that once you get used to DAX, you will find the behavior very predictable and easy to “debug” also for more complex allocation formula. You just have to be careful in writing the DAX formula, but probably the pattern we wrote should help you designing the right data model, without creating physical relationships to the budget table! This pattern is also based on the Handling Different Granularities scenario I discussed a couple of weeks ago.

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  • SSAS Native v .net Provider

    - by ACALVETT
    Recently I was investigating why a new server which is in its parallel running phase was taking significantly longer to process the daily data than the server its due to replace. The server has SQL & SSAS installed so the problem was not likely to be in the network transfer as its using shared memory. As i dug around the SQL dmv’s i noticed in sys.dm_exec_connections that the SSAS connection had a packet size of 8000 bytes instead of the usual 4096 bytes and from there i found that the datasource...(read more)

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  • Help with algorithmic complexity in custom merge sort implementation

    - by bitcycle
    I've got an implementation of the merge sort in C++ using a custom doubly linked list. I'm coming up with a big O complexity of n^2, based on the merge_sort() slice operation. But, from what I've read, this algorithm should be n*log(n), where the log has a base of two. Can someone help me determine if I'm just determining the complexity incorrectly, or if the implementation can/should be improved to achieve n*log(n) complexity? If you would like some background on my goals for this project, see my blog. I've added comments in the code outlining what I understand the complexity of each method to be. Clarification - I'm focusing on the C++ implementation with this question. I've got another implementation written in Python, but that was something that was added in addition to my original goal(s).

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  • What skills should a developer/tester learn in order to move into a permanent Systems Analysis role?

    - by shenaz
    I have been with a software services firm for 5 years and have fallen into a "jack of all trades" role, which I am looking to move out of. I've spent about 1 year each in programming (VB/VB.NET), application support, systems analysis, and most recently, software testing, which in my current position is all manual. I've really lost interest in the programming and testing roles; I would prefer a position where I get to work more with people, such as systems analysis. I even got a chance to be a trainer at the same company for a few months, a temporary position which I enjoyed very much. Given that most of my real experience is with software, support, and testing, what knowledge areas and skills should I focus on learning and mastering in order to make myself an attractive candidate for a permanent position as a business/systems analyst?

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  • New licensing for SQL Server 2012 and #BISM #Tabular usage

    - by Marco Russo (SQLBI)
    Last week Microsoft announced a new licensing schema for SQL Server 2012. If you are interested in an extensive discussion of the new licensing scheme, Denny Cherry wrote a great blog post about that. I’d like to comment about the new BI Edition license. Teo Lachev already commented about the numbers and I agree with him. I generally like the new licensing mode of SQL 2012. It maintains a very low-entry barrier for SSRS/SSAS/SSIS (Standard Edition). It has a reasonable licensing schema for 20-50...(read more)

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  • Strategy to find bottleneck in a network

    - by Simone
    Our enterprise is having some problem when the number of incoming request goes beyond a certain amount. To make things simpler, we have N websites that uses, amongst other, a local web service. This service is hosted by IIS, and it's a .NET 4.0 (C#) application executed in a farm. It's REST-oriented, built around OpenRasta. As already mentioned, by stress testing it with JMeter, we've found that beyond a certain amount of request the service's performance drop. Anyway, this service is, amongst other, a client itself of other 3 distinct web services and also a client for a DB server, so it's not very clear what really is the culprit of this abrupt decay. In turn, these 3 other web services are installed in our farm too, and client of other DB servers (and services, possibly, that are out of my team control). What strategy do you suggest to try to locate where the bottleneck(s) are? Do you have any high-level suggestions?

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  • How meaningful is the Big-O time complexity of an algorithm?

    - by james creasy
    Programmers often talk about the time complexity of an algorithm, e.g. O(log n) or O(n^2). Time complexity classifications are made as the input size goes to infinity, but ironically infinite input size in computation is not used. Put another way, the classification of an algorithm is based on a situation that algorithm will never be in: where n = infinity. Also, consider that a polynomial time algorithm where the exponent is huge is just as useless as an exponential time algorithm with tiny base (e.g., 1.00000001^n) is useful. Given this, how much can I rely on the Big-O time complexity to advise choice of an algorithm?

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  • Watch @marcorus and @ferrarialberto sessions online #teched #msteched #tee2012

    - by Marco Russo (SQLBI)
    In June I participated to two TechEd editions (North America and Europe). I and Alberto delivered a Pre Conference and two sessions about Tabular. Both conferences provides recorded sessions freely available on Channel 9 so that you can compare which one has been delivered in the best way! If you have to choose between the two versions, consider that in North America we receive more questions during and after the session (still recording), increasing the interaction, whereas in Europe questions usually comes after the session finished (so no recording available). If you’re curious, watch both and let me know which version you prefer, especially for Multidimensional vs Tabular! BISM: Multidimensional vs. Tabular (TechEd North America 2012) BISM: Multidimensional vs. Tabular (TechEd Europe 2012) Many-to-Many Relationships in BISM Tabular (TechEd North America 2012) Many-to-Many Relationships in BISM Tabular (TechEd Europe 2012) If you are interested to learn SSAS Tabular, don’t miss the next SSAS Tabular Workshop online on September 3-4, 2012. We are also planning dates for another roadshow in Europe this fall and I’m happy to announce we’ll have two dates in Germany, too. More updates in the coming weeks.

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  • Adventures in the Land of CloudDB/NoSQL/NoAcid

    - by KKline
    Cloud, Bunny, or CloudBunny? Last year, some of my friends from Quest Software attended Hadoop World in New York. In 2009, I never would've guessed that Quest would be there with products, community initiatives, as a major sponsor and with presenters? There were just under 1,000 attendees who weren’t the typical devheads and geekasaurs you'd normally see at very techie events like Code Camps, SQL Saturdays, Cloud Camps and or even other NoSQL events such as the Cassandra Summit. We're talkin' enterprise...(read more)

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  • Watch @marcorus and @ferrarialberto sessions online #teched #msteched #tee2012

    - by Marco Russo (SQLBI)
    In June I participated to two TechEd editions (North America and Europe). I and Alberto delivered a Pre Conference and two sessions about Tabular. Both conferences provides recorded sessions freely available on Channel 9 so that you can compare which one has been delivered in the best way! If you have to choose between the two versions, consider that in North America we receive more questions during and after the session (still recording), increasing the interaction, whereas in Europe questions usually comes after the session finished (so no recording available). If you’re curious, watch both and let me know which version you prefer, especially for Multidimensional vs Tabular! BISM: Multidimensional vs. Tabular (TechEd North America 2012) BISM: Multidimensional vs. Tabular (TechEd Europe 2012) Many-to-Many Relationships in BISM Tabular (TechEd North America 2012) Many-to-Many Relationships in BISM Tabular (TechEd Europe 2012) If you are interested to learn SSAS Tabular, don’t miss the next SSAS Tabular Workshop online on September 3-4, 2012. We are also planning dates for another roadshow in Europe this fall and I’m happy to announce we’ll have two dates in Germany, too. More updates in the coming weeks.

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  • SQL Bits X – Temporal Snapshot Fact Table Session Slide & Demos

    - by Davide Mauri
    Already 10 days has passed since SQL Bits X in London. I really enjoyed it! Those kind of events are great not only for the content but also to meet friends that – due to distance – is not possible to meet every day. Friends from PASS, SQL CAT, Microsoft, MVP and so on all in one place, drinking beers, whisky and having fun. A perfect mixture for a great learning and sharing experience! I’ve also enjoyed a lot delivering my session on Temporal Snapshot Fact Tables. Given that the subject is very specific I was not expecting a lot of attendees….but I was totally wrong! It seems that the problem of handling daily snapshot of data is more common than what I expected. I’ve also already had feedback from several attendees that applied the explained technique to their existing solution with success. This is just what a speaker in such conference wish to hear! :) If you want to take a look at the slides and the demos, you can find them on SkyDrive: https://skydrive.live.com/redir.aspx?cid=377ea1391487af21&resid=377EA1391487AF21!1151&parid=root The demo is available both for SQL Sever 2008 and for SQL Server 2012. With this last version, you can also simplify the ETL process using the new LEAD analytic function. (This is not done in the demo, I’ve left this option as a little exercise for you :) )

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  • how do you manage application performance reviews

    - by CoolBeans
    I have been trying to figure out ways to effectively do performance reviews before an install happens for all releases done by our team. Do you usually make this a part of code review process or do you handle it as a separate review task? FYI - we do not have a dedicated performance testing team. It is up to the developers to make sure the app performs well. The apps I am referring to are web applications.

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  • How to read Scala code with lots of implicits?

    - by Petr Pudlák
    Consider the following code fragment (adapted from http://stackoverflow.com/a/12265946/1333025): // Using scalaz 6 import scalaz._, Scalaz._ object Example extends App { case class Container(i: Int) def compute(s: String): State[Container, Int] = state { case Container(i) => (Container(i + 1), s.toInt + i) } val d = List("1", "2", "3") type ContainerState[X] = State[Container, X] println( d.traverse[ContainerState, Int](compute) ! Container(0) ) } I understand what it does on high level. But I wanted to trace what exactly happens during the call to d.traverse at the end. Clearly, List doesn't have traverse, so it must be implicitly converted to another type that does. Even though I spent a considerable amount of time trying to find out, I wasn't very successful. First I found that there is a method in scalaz.Traversable traverse[F[_], A, B] (f: (A) => F[B], t: T[A])(implicit arg0: Applicative[F]): F[T[B]] but clearly this is not it (although it's most likely that "my" traverse is implemented using this one). After a lot of searching, I grepped scalaz source codes and I found scalaz.MA's method traverse[F[_], B] (f: (A) => F[B])(implicit a: Applicative[F], t: Traverse[M]): F[M[B]] which seems to be very close. Still I'm missing to what List is converted in my example and if it uses MA.traverse or something else. The question is: What procedure should I follow to find out what exactly is called at d.traverse? Having even such a simple code that is so hard analyze seems to me like a big problem. Am I missing something very simple? How should I proceed when I want to understand such code that uses a lot of imported implicits? Is there some way to ask the compiler what implicits it used? Or is there something like Hoogle for Scala so that I can search for a method just by its name?

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  • Given an XML which contains a representation of a graph, how to apply it DFS algorithm? [on hold]

    - by winston smith
    Given the followin XML which is a directed graph: <?xml version="1.0" encoding="iso-8859-1" ?> <!DOCTYPE graph PUBLIC "-//FC//DTD red//EN" "../dtd/graph.dtd"> <graph direct="1"> <vertex label="V0"/> <vertex label="V1"/> <vertex label="V2"/> <vertex label="V3"/> <vertex label="V4"/> <vertex label="V5"/> <edge source="V0" target="V1" weight="1"/> <edge source="V0" target="V4" weight="1"/> <edge source="V5" target="V2" weight="1"/> <edge source="V5" target="V4" weight="1"/> <edge source="V1" target="V2" weight="1"/> <edge source="V1" target="V3" weight="1"/> <edge source="V1" target="V4" weight="1"/> <edge source="V2" target="V3" weight="1"/> </graph> With this classes i parsed the graph and give it an adjacency list representation: import java.io.IOException; import java.util.HashSet; import java.util.LinkedList; import java.util.Collection; import java.util.Iterator; import java.util.logging.Level; import java.util.logging.Logger; import practica3.util.Disc; public class ParsingXML { public static void main(String[] args) { try { // TODO code application logic here Collection<Vertex> sources = new HashSet<Vertex>(); LinkedList<String> lines = Disc.readFile("xml/directed.xml"); for (String lin : lines) { int i = Disc.find(lin, "source=\""); String data = ""; if (i > 0 && i < lin.length()) { while (lin.charAt(i + 1) != '"') { data += lin.charAt(i + 1); i++; } Vertex v = new Vertex(); v.setName(data); v.setAdy(new HashSet<Vertex>()); sources.add(v); } } Iterator it = sources.iterator(); while (it.hasNext()) { Vertex ver = (Vertex) it.next(); Collection<Vertex> adyacencias = ver.getAdy(); LinkedList<String> ls = Disc.readFile("xml/graphs.xml"); for (String lin : ls) { int i = Disc.find(lin, "target=\""); String data = ""; if (lin.contains("source=\""+ver.getName())) { Vertex v = new Vertex(); if (i > 0 && i < lin.length()) { while (lin.charAt(i + 1) != '"') { data += lin.charAt(i + 1); i++; } v.setName(data); } i = Disc.find(lin, "weight=\""); data = ""; if (i > 0 && i < lin.length()) { while (lin.charAt(i + 1) != '"') { data += lin.charAt(i + 1); i++; } v.setWeight(Integer.parseInt(data)); } if (v.getName() != null) { adyacencias.add(v); } } } } for (Vertex vert : sources) { System.out.println(vert); System.out.println("adyacencias: " + vert.getAdy()); } } catch (IOException ex) { Logger.getLogger(ParsingXML.class.getName()).log(Level.SEVERE, null, ex); } } } This is another class: import java.util.Collection; import java.util.Objects; public class Vertex { private String name; private int weight; private Collection ady; public Collection getAdy() { return ady; } public void setAdy(Collection adyacencias) { this.ady = adyacencias; } public String getName() { return name; } public void setName(String nombre) { this.name = nombre; } public int getWeight() { return weight; } public void setWeight(int weight) { this.weight = weight; } @Override public int hashCode() { int hash = 7; hash = 43 * hash + Objects.hashCode(this.name); hash = 43 * hash + this.weight; return hash; } @Override public boolean equals(Object obj) { if (obj == null) { return false; } if (getClass() != obj.getClass()) { return false; } final Vertex other = (Vertex) obj; if (!Objects.equals(this.name, other.name)) { return false; } if (this.weight != other.weight) { return false; } return true; } @Override public String toString() { return "Vertice{" + "name=" + name + ", weight=" + weight + '}'; } } And finally: /** * * @author user */ /* -*-jde-*- */ /* <Disc.java> Contains the main argument*/ import java.io.*; import java.util.LinkedList; /** * Lectura y escritura de archivos en listas de cadenas * Ideal para el uso de las clases para gráficas. * * @author Peralta Santa Anna Victor Miguel * @since Julio 2011 */ public class Disc { /** * Metodo para lectura de un archivo * * @param fileName archivo que se va a leer * @return El archivo en representacion de lista de cadenas */ public static LinkedList<String> readFile(String fileName) throws IOException { BufferedReader file = new BufferedReader(new FileReader(fileName)); LinkedList<String> textlist = new LinkedList<String>(); while (file.ready()) { textlist.add(file.readLine().trim()); } file.close(); /* for(String linea:textlist){ if(linea.contains("source")){ //String generado = linea.replaceAll("<\\w+\\s+\"", ""); //System.out.println(generado); } }*/ return textlist; }//readFile public static int find(String linea,String palabra){ int i,j; boolean found = false; for(i=0,j=0;i<linea.length();i++){ if(linea.charAt(i)==palabra.charAt(j)){ j++; if(j==palabra.length()){ found = true; return i; } }else{ continue; } } if(!found){ i= -1; } return i; } /** * Metodo para la escritura de un archivo * * @param fileName archivo que se va a escribir * @param tofile la lista de cadenas que quedaran en el archivo * @param append el bit que dira si se anexa el contenido o se empieza de cero */ public static void writeFile(String fileName, LinkedList<String> tofile, boolean append) throws IOException { FileWriter file = new FileWriter(fileName, append); for (int i = 0; i < tofile.size(); i++) { file.write(tofile.get(i) + "\n"); } file.close(); }//writeFile /** * Metodo para escritura de un archivo * @param msg archivo que se va a escribir * @param tofile la cadena que quedaran en el archivo * @param append el bit que dira si se anexa el contenido o se empieza de cero */ public static void writeFile(String msg, String tofile, boolean append) throws IOException { FileWriter file = new FileWriter(msg, append); file.write(tofile); file.close(); }//writeFile }// I'm stuck on what can be the best way to given an adjacency list representation of the graph how to apply it Depth-first search algorithm. Any idea of how to aproach to complete the task?

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  • Implement Budget Allocation in DAX for Power Pivot and Tabular #powerpivot #tabular #ssas #dax

    - by Marco Russo (SQLBI)
    Comparing sales and budget, or costs and budget, is a very common operation. However, it is often the case that you have different granularities for different tables containing budget and the data to compare with. There are two ways to do that: you can limit the comparison to the granularity that is common to the two tables, or you can allocate the budget where it’s not defined. For example, if you have a budget defined by quarter and category, you might want to allocate it by month and product. In this way, you will do the comparison as you had a more granular definition of the budget, without actually having to do the manual job of allocating data (usually in an Excel worksheet!). If you want to do budget allocation in DAX, you can use the Budget Patterns we published on DAX Patterns. If you come from and MDX/OLAP background, at first you might find it hard to solve the problem of not having attribute hierarchies that helps you in propagating the budget values to lower hierarchical levels. However, I think that once you get used to DAX, you will find the behavior very predictable and easy to “debug” also for more complex allocation formula. You just have to be careful in writing the DAX formula, but probably the pattern we wrote should help you designing the right data model, without creating physical relationships to the budget table! This pattern is also based on the Handling Different Granularities scenario I discussed a couple of weeks ago.

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  • SSAS Tabular Workshop online and other upcoming dates (and updates!) #ssas #tabular

    - by Marco Russo (SQLBI)
    After many conferences and travels, this summer I had some time to write and prepare new sessions for the next wave of conferences. In reality I am just doing that, even if I already restarted traveling for consulting and training. So expect new content about DAX and Tabular coming in the next months! Starting to see real customer adopting Tabular is showing many new challenges and there is still a lot to learn and to create. If you still didn’t started working on Tabular, well, you should. As I always say, as a BI developer you should be able to choose between Tabular and Multidimensional, and in order to do that you should know both of them! One thing that I don’t like very much about marketing is that “Tabular is simpler”, because it’s often translated in “Tabular is for simple projects” when this last statement is not true. Actually, I see a lot of good reasons to adopt Tabular in complex data models, especially in non-traditional scenarios. I know, this is because I love to understand what are the actual limits of a technology, and I’m learning that there is simple a lot of space of improvement also for Tabular. It’s already fast, but it could be faster! How can you start? Well, first of all, by reading our book. Then, by attending to our SSAS Tabular workshop. There is an online edition of the workshop on September 3-4, 2012 (hurry up if you want to register), and there are already several dates planned for the next months (and others will be added soon!). And, of course, by installing SQL Server 2012 and trying to create models over your databases. If you are too lazy, just start with PowerPivot. As soon as you start working with Tabular or PowerPivot, you will see that there is one important skill you need: learning DAX. In the next few days I should publish an article that I’m finishing these days about best practices using SUMMARIZE and ADDCOLUMNS. If only someone published this article one year ago, I would have saved many hours of my life. But, you know, flight manuals are written in blood… and someone has to write! Stay tuned.

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  • Telecomunication SID model and resources [on hold]

    - by andygluk
    There is a SID model well-known in telecom industry. Following this model you define resources as resources owned by your enterprise, and then you build resource-oriented services on top of it and then customer-oriented services and so on... So everything is based on enterprise-owned resources, which you have to identify first. What I am looking for and what I am asking is some alternative to this model, build not on enterprise-owned resources, but on resources sell by enterprise. Say, you are selling licenses for using your products. So instead of building model on top of enterprise resources you may be interested to build it on top of licenses you are selling.

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  • Sentence Tree v/s Words List

    - by Rohit Jose
    I was recently tasked with building a Name Entity Recognizer as part of a project. The objective was to parse a given sentence and come up with all the possible combinations of the entities. One approach that was suggested was to keep a lookup table for all the know connector words like articles and conjunctions, remove them from the words list after splitting the sentence on the basis of the spaces. This would leave out the Name Entities in the sentence. A lookup is then done for these identified entities on another lookup table that associates them to the entity type, for example if the sentence was: Remember the Titans was a movie directed by Boaz Yakin, the possible outputs would be: {Remember the Titans,Movie} was {a movie,Movie} directed by {Boaz Yakin,director} {Remember the Titans,Movie} was a movie directed by Boaz Yakin {Remember the Titans,Movie} was {a movie,Movie} directed by Boaz Yakin {Remember the Titans,Movie} was a movie directed by {Boaz Yakin,director} Remember the Titans was {a movie,Movie} directed by Boaz Yakin Remember the Titans was {a movie,Movie} directed by {Boaz Yakin,director} Remember the Titans was a movie directed by {Boaz Yakin,director} Remember the {the titans,Movie,Sports Team} was {a movie,Movie} directed by {Boaz Yakin,director} Remember the {the titans,Movie,Sports Team} was a movie directed by Boaz Yakin Remember the {the titans,Movie,Sports Team} was {a movie,Movie} directed by Boaz Yakin Remember the {the titans,Movie,Sports Team} was a movie directed by {Boaz Yakin,director} The entity lookup table here would contain the following data: Remember the Titans=Movie a movie=Movie Boaz Yakin=director the Titans=Movie the Titans=Sports Team Another alternative logic that was put forward was to build a crude sentence tree that would contain the connector words in the lookup table as parent nodes and do a lookup in the entity table for the leaf node that might contain the entities. The tree that was built for the sentence above would be: The question I am faced with is the benefits of the two approaches, should I be going for the tree approach to represent the sentence parsing, since it provides a more semantic structure? Is there a better approach I should be going for solving it?

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  • Optimize Many-to-Many with SUMMARIZE and Other Techniques

    - by Marco Russo (SQLBI)
    We are still in the early days of DAX and even if I have been using it since 2 years ago, there is still a lot to learn on that. One of the topics that historically interests me (and many of the readers here, probably) is the many-to-many relationships between dimensions in a dimensional data model. When I and Alberto wrote the The Many to Many Revolution 2.0 we discovered the SUMMARIZE based pattern very late in the whitepaper writing. It is very important for performance optimization and it should be always used. In the last month, Gerhard Brueckl also presented an approach based on cross table filtering behavior that simplify the syntax involved, even if it’s harder to explain how it works internally. I published a short article titled Optimize Many-to-Many Calculation in DAX with SUMMARIZE and Cross Table Filtering on SQLBI website just to provide a quick reference to the three patterns available. A further study is still required to compare performance between SUMMARIZE and Cross Table Filtering patterns. Up to now, I haven’t observed big differences between them, even if their execution plans might be not identical and this suggest me that depending on other conditions you might favor one over the other.

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  • Does it matter the direction of a Huffman's tree child node?

    - by Omega
    So, I'm on my quest about creating a Java implementation of Huffman's algorithm for compressing/decompressing files (as you might know, ever since Why create a Huffman tree per character instead of a Node?) for a school assignment. I now have a better understanding of how is this thing supposed to work. Wikipedia has a great-looking algorithm here that seemed to make my life way easier. Taken from http://en.wikipedia.org/wiki/Huffman_coding: Create a leaf node for each symbol and add it to the priority queue. While there is more than one node in the queue: Remove the two nodes of highest priority (lowest probability) from the queue Create a new internal node with these two nodes as children and with probability equal to the sum of the two nodes' probabilities. Add the new node to the queue. The remaining node is the root node and the tree is complete. It looks simple and great. However, it left me wondering: when I "merge" two nodes (make them children of a new internal node), does it even matter what direction (left or right) will each node be afterwards? I still don't fully understand Huffman coding, and I'm not very sure if there is a criteria used to tell whether a node should go to the right or to the left. I assumed that, perhaps the highest-frequency node would go to the right, but I've seen some Huffman trees in the web that don't seem to follow such criteria. For instance, Wikipedia's example image http://upload.wikimedia.org/wikipedia/commons/thumb/8/82/Huffman_tree_2.svg/625px-Huffman_tree_2.svg.png seems to put the highest ones to the right. But other images like this one http://thalia.spec.gmu.edu/~pparis/classes/notes_101/img25.gif has them all to the left. However, they're never mixed up in the same image (some to the right and others to the left). So, does it matter? Why?

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  • Androids development life cycle model query [closed]

    - by Andrew Rose
    I have been currently researching Google and their approach to marketing the Android OS. Primarily using an open source technique with the Open Hand Alliance and out souring through third-party developers. I'm now keen to investigate their approach using various development life cycle models in the form of waterfall, spiral, scrum, agile etc. And i'm just curious to have some feedback from professionals and what approach they think Google would use to have a positive effect on their business. Thanks for your time Andy Rose

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  • #DAX Query Plan in SQL Server 2012 #Tabular

    - by Marco Russo (SQLBI)
    The SQL Server Profiler provides you many information regarding the internal behavior of DAX queries sent to a BISM Tabular model. Similar to MDX, also in DAX there is a Formula Engine (FE) and a Storage Engine (SE). The SE is usually handled by Vertipaq (unless you are using DirectQuery mode) and Vertipaq SE Query classes of events gives you a SQL-like syntax that represents the query sent to the storage engine. Another interesting class of events is the DAX Query Plan , which contains a couple...(read more)

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