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  • SQL SERVER – Guest Post – Architecting Data Warehouse – Niraj Bhatt

    - by pinaldave
    Niraj Bhatt works as an Enterprise Architect for a Fortune 500 company and has an innate passion for building / studying software systems. He is a top rated speaker at various technical forums including Tech·Ed, MCT Summit, Developer Summit, and Virtual Tech Days, among others. Having run a successful startup for four years Niraj enjoys working on – IT innovations that can impact an enterprise bottom line, streamlining IT budgets through IT consolidation, architecture and integration of systems, performance tuning, and review of enterprise applications. He has received Microsoft MVP award for ASP.NET, Connected Systems and most recently on Windows Azure. When he is away from his laptop, you will find him taking deep dives in automobiles, pottery, rafting, photography, cooking and financial statements though not necessarily in that order. He is also a manager/speaker at BDOTNET, Asia’s largest .NET user group. Here is the guest post by Niraj Bhatt. As data in your applications grows it’s the database that usually becomes a bottleneck. It’s hard to scale a relational DB and the preferred approach for large scale applications is to create separate databases for writes and reads. These databases are referred as transactional database and reporting database. Though there are tools / techniques which can allow you to create snapshot of your transactional database for reporting purpose, sometimes they don’t quite fit the reporting requirements of an enterprise. These requirements typically are data analytics, effective schema (for an Information worker to self-service herself), historical data, better performance (flat data, no joins) etc. This is where a need for data warehouse or an OLAP system arises. A Key point to remember is a data warehouse is mostly a relational database. It’s built on top of same concepts like Tables, Rows, Columns, Primary keys, Foreign Keys, etc. Before we talk about how data warehouses are typically structured let’s understand key components that can create a data flow between OLTP systems and OLAP systems. There are 3 major areas to it: a) OLTP system should be capable of tracking its changes as all these changes should go back to data warehouse for historical recording. For e.g. if an OLTP transaction moves a customer from silver to gold category, OLTP system needs to ensure that this change is tracked and send to data warehouse for reporting purpose. A report in context could be how many customers divided by geographies moved from sliver to gold category. In data warehouse terminology this process is called Change Data Capture. There are quite a few systems that leverage database triggers to move these changes to corresponding tracking tables. There are also out of box features provided by some databases e.g. SQL Server 2008 offers Change Data Capture and Change Tracking for addressing such requirements. b) After we make the OLTP system capable of tracking its changes we need to provision a batch process that can run periodically and takes these changes from OLTP system and dump them into data warehouse. There are many tools out there that can help you fill this gap – SQL Server Integration Services happens to be one of them. c) So we have an OLTP system that knows how to track its changes, we have jobs that run periodically to move these changes to warehouse. The question though remains is how warehouse will record these changes? This structural change in data warehouse arena is often covered under something called Slowly Changing Dimension (SCD). While we will talk about dimensions in a while, SCD can be applied to pure relational tables too. SCD enables a database structure to capture historical data. This would create multiple records for a given entity in relational database and data warehouses prefer having their own primary key, often known as surrogate key. As I mentioned a data warehouse is just a relational database but industry often attributes a specific schema style to data warehouses. These styles are Star Schema or Snowflake Schema. The motivation behind these styles is to create a flat database structure (as opposed to normalized one), which is easy to understand / use, easy to query and easy to slice / dice. Star schema is a database structure made up of dimensions and facts. Facts are generally the numbers (sales, quantity, etc.) that you want to slice and dice. Fact tables have these numbers and have references (foreign keys) to set of tables that provide context around those facts. E.g. if you have recorded 10,000 USD as sales that number would go in a sales fact table and could have foreign keys attached to it that refers to the sales agent responsible for sale and to time table which contains the dates between which that sale was made. These agent and time tables are called dimensions which provide context to the numbers stored in fact tables. This schema structure of fact being at center surrounded by dimensions is called Star schema. A similar structure with difference of dimension tables being normalized is called a Snowflake schema. This relational structure of facts and dimensions serves as an input for another analysis structure called Cube. Though physically Cube is a special structure supported by commercial databases like SQL Server Analysis Services, logically it’s a multidimensional structure where dimensions define the sides of cube and facts define the content. Facts are often called as Measures inside a cube. Dimensions often tend to form a hierarchy. E.g. Product may be broken into categories and categories in turn to individual items. Category and Items are often referred as Levels and their constituents as Members with their overall structure called as Hierarchy. Measures are rolled up as per dimensional hierarchy. These rolled up measures are called Aggregates. Now this may seem like an overwhelming vocabulary to deal with but don’t worry it will sink in as you start working with Cubes and others. Let’s see few other terms that we would run into while talking about data warehouses. ODS or an Operational Data Store is a frequently misused term. There would be few users in your organization that want to report on most current data and can’t afford to miss a single transaction for their report. Then there is another set of users that typically don’t care how current the data is. Mostly senior level executives who are interesting in trending, mining, forecasting, strategizing, etc. don’t care for that one specific transaction. This is where an ODS can come in handy. ODS can use the same star schema and the OLAP cubes we saw earlier. The only difference is that the data inside an ODS would be short lived, i.e. for few months and ODS would sync with OLTP system every few minutes. Data warehouse can periodically sync with ODS either daily or weekly depending on business drivers. Data marts are another frequently talked about topic in data warehousing. They are subject-specific data warehouse. Data warehouses that try to span over an enterprise are normally too big to scope, build, manage, track, etc. Hence they are often scaled down to something called Data mart that supports a specific segment of business like sales, marketing, or support. Data marts too, are often designed using star schema model discussed earlier. Industry is divided when it comes to use of data marts. Some experts prefer having data marts along with a central data warehouse. Data warehouse here acts as information staging and distribution hub with spokes being data marts connected via data feeds serving summarized data. Others eliminate the need for a centralized data warehouse citing that most users want to report on detailed data. Reference: Pinal Dave (http://blog.SQLAuthority.com) Filed under: Best Practices, Business Intelligence, Data Warehousing, Database, Pinal Dave, PostADay, Readers Contribution, SQL, SQL Authority, SQL Query, SQL Server, SQL Tips and Tricks, T SQL, Technology

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  • Can I implement the readers and writers algorithm in OpenMP by replacing counting semaphores with another feature?

    - by DeveloperDon
    After reading about OpenMP and not finding functions to support semaphores, I did an internet search for OpenMP and the readers and writers problem, but found no suitable matches. Is there a general method for replacing counting semaphores in OpenMP with something that it supports? Or is there just a gap in the environment where it does not permit things that are asymmetrical like the third readers and writers problem shown on the following page? http://en.wikipedia.org/wiki/Readers-writers_problem#The_third_readers-writers_problem

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  • How to ask the boss to pay for training courses

    - by jiceo
    Recently I came upon a well known local consulting company that has some interesting courses I'd like to take. The course is not cheap enough for me to pay out of my own pocket and not feel bad afterwards. The thing is that my startup company uses one set of framework (Python+Django) for most of the stuff I have to deal with, but the course covers Ruby on Rails 3. Since I've not had exposure to Ruby on Rails, and after seeing so many people speak highly of the course, I really thought it would be a good opportunity. I know that I'd have to approach my boss at the angle of 'how this might benefit the company' but other than this, any suggestions?

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  • Questions to ask a 3rd party API provider

    - by Jarede
    I'm due to meet with a developer/sales person from a new 3rd party resource we're about to start using. The main topic I'll be interested in, is their API as I will be the developer making use of it and explaining it to the rest of the team. What questions would you recommend asking? Things I'm already thinking about are: What happens and how will I be notified when they depreciate a method? Is there ever any downtime? Who will I deal with first when I have API issues?

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  • 5 Must-Ask Questions For Your Business Website Developer

    The wrong way to hire a website developer is to use a directory. The right way is to use recommendations from people you know, or even that you don't know - by writing them email and explaining that you love their site design - and asking who did it and whether the developer was easy to work with.

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  • Watch Ask the Gu on Channel 9 Live

    Scott Guthrie was kind enough to join the Channel 9 Live crew for an discussion of everything Silverlight immediately following his Silverlight 4 launch keynote. You can check out the recorded video right on Channel 9. Scott does a great job fielding the questions from the audience and from Twitter. Charles Torre is a great moderator he asks some great questions in addition to the flurry that came in from Twitter. I love when he asks Scott how we can release Silverlight versions at such a fast...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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  • How to ask questions on the Forums

    - by TATWORTH
    Based upon answering many questions on forums such as forums.asp.net, here are some tips on getting your questions answered, once you have exhausted searching on your own. Choose a concise but meaningful title but avoid words like "urgent" Post to the correct section of the forum - some people specialise in a particular section of a given forum Make it clear that you have already made an effort to answer yourself. Summerise the environmental context of your question e.g. If using SQL then state the version e.g. SQLExpress 2008 If you need to post a code or markup sample, tidy it up by removing extraneous blank lines and set the tab spacing to 2 rather than 4. Take your time composing the question so that it is set out as clearly as possible. Remember that the majority of people providing answers do so in their own time. Be very polite and thank those that help you.

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  • Everything you wanted to know about private database clouds, but were afraid to ask

    - by B R Clouse
    Private Database Clouds have come into their own, and will be a prominent topic at Oracle OpenWorld this year.  In fact while most exhibits will be open from Monday through Wednesday, Private Database Clouds will be available starting Sunday afternoon all the way through Thursday evening.  In addition to the demonstration choices, numerous speaking sessions address Private Database Clouds, including a general session on Monday.  The demos and discussions will help  you chart your path to cloud computing.

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  • 3 Important Questions to Ask Google Analytics

    With dozens of free web analytics tools available in the market, Google Analytics stands out because it provides data like no other tool does. Just add a few lines of JavaScript code to your website';... [Author: Debbie Everson - Web Design and Development - April 02, 2010]

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  • Ask HTG: Searching Within Websites, Google Play Alternatives, and Getting Started with Dual Booting

    - by Jason Fitzpatrick
    Once a week we round up some of the reader letters we’ve answered and share the advice with everyone. This week we’re looking at how to search within web sites, downloading apps from places other than Google Play, and getting started with dual booting operating systems. The Best Free Portable Apps for Your Flash Drive Toolkit How to Own Your Own Website (Even If You Can’t Build One) Pt 3 How to Sync Your Media Across Your Entire House with XBMC

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  • Do they ask too much on this job?

    - by user58404
    I am looking for web developer job and this job description caught my eyes. I am not sure how much they offer but I was wondering if anyone here meets all of their requirements? To me, that's a lot of knowledge. 2 to 4+ years experience building web sites and applications in a professional environment Strong working knowledge of HTML5 and CSS3 Strong working knowledge of JavaScript, jQuery, AJAX Working knowledge of Ruby on Rails or similar MVC framework Working knowledge of ExpressionEngine, Wordpress or similar CMS Experience administering a LAMP-based server Experience with cross-platform and cross-browser website testing Comfortable working with version control (preferably Git) Proficient with Adobe Photoshop, Illustrator, and Fireworks Comfortable working on a Mac Self-starter with excellent time-management skills with the ability to meet challenging deadlines Ability to work independently with minimal supervision Desire to work on a small team Bonus Skills: Experience deploying to Heroku or similar PaaS provider. Experience developing Facebook applications A strong sense of design Cool open source projects (send us your Github account!) Advanced working knowledge of server administration and website deployment. Java and/or .NET experience

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