Most important point to make about Analysis Services 2012 is that it is really two products in one. Analysis Services in the SQL Server 2008 R2 release and before is still present, but it is now called the Multidimensional model. It has had a few improvements relating to performance, scalability, and manageability, but there is no new major functionality. Meanwhile, there is a new version of Analysis Services that closely resembles PowerPivot—this is called the Tabular model.
What Is the BI Semantic Model?
One term that has been mentioned a lot in the discussions about Analysis Services 2012 is the BI Semantic Model or BISM. This term does not refer to either the Multidimensional or Tabular models specifically but, instead, describes the function of Analysis Services in the Microsoft BI stack: the fact that it acts as a semantic layer on top of a relational data warehouse, adding a rich layer of metadata that includes hierarchies, measures, and calculations. In that respect, it is very similar to the term Unified Dimensional Model that was used around the time of the SQL Server 2005 launch. In some cases, the term BI Semantic Model has referred to the Tabular model only, but this is not correct.
Why Have Two Models?
Why has this split happened? Although Microsoft does not want to make any public comments on this topic, there are a number of likely reasons.
- Analysis Services Multidimensional is getting old. It was designed in an age of 32-bit servers with one or two processors and less than a gigabyte of RAM, when disk-based storage was the only option for databases. Times have changed, and modern hardware is radically different; now a new generation of memory-based, columnar databases has set the standard for query performance with analytic workloads, and Analysis Services must adopt this new 10 Microsoft SQL Server 2012 Analysis Services: The BISM Tabular Model technology to keep up. Retrofitting the new xVelocity in-memory engine into the existing Multidimensional model was not, however, a straightforward job, so it was necessary to introduce the new Tabular model to take full advantage of xVelocity.
- Despite the success of Analysis Services Multidimensional, there has always been a perception that it is difficult to learn. Some database professionals, accustomed to relational data modeling, struggle to learn multidimensional concepts, and those that do find the learning curve is steep. Therefore, if Microsoft wants to bring BI to an ever-wider audience, it must simplify the development process—hence the move from the complex world of the Multidimensional model to the relatively simple and familiar concepts of the Tabular model.
- Microsoft sees self-service BI as a huge potential source of growth, and PowerPivot is its entry into this market. It is also important to have consistency between the Microsoft self-service and corporate BI tools. Therefore, if Analysis Services must be overhauled, it makes sense to make it compatible with PowerPivot, with a similar design experience so self-service models can easily be upgraded to full-fledged corporate solutions.
- Some types of data are more appropriately, or more easily, modeled by using the Tabular approach, and some types of data are more appropriate for a Multidimensional approach. Having different models gives developers the choice to use whichever approach suits their circumstances.
The Future of Analysis Services
Having two models inside Analysis Services, plus two query and calculation languages, is clearly not an ideal state of affairs. First and foremost, it means you have to choose which model to use at the start of your project, when you might not know enough about your requirements to know which one is appropriate—and this is the question we will address in the next section. It also means that anyone who decides to specialize in Analysis Services has to learn two technologies. Presumably, this state of affairs will not continue in the long term.
Microsoft has been very clear in saying that the Multidimensional model is not deprecated and that the Tabular model is not its replacement. It is likely that new features for Multidimensional will be released in future versions of Analysis Services. The fact that the Tabular and Multidimensional models share some of the same code suggests that some new features could easily be developed for both models simultaneously. The post on the Analysis Services blog previously referenced suggests that in time the two models will converge and offer much the same functionality, so the decision about which model to use is based on whether the developer prefers to use a multidimensional or relational way of modeling data. Support for DAX queries in the Multidimensional model, when it arrives, will represent one step in this direction.
One other thing is clear about the future of Analysis Services: It will be moving to the cloud. Microsoft has confirmed it is working on a cloud-based version of Analysis Services and this, plus SQL Azure, SQL Azure Reporting Services, and Office 365, will form the core of the Microsoft cloud BI strategy.