|So, what is the BI Semantic Model?|
|Written by Chris Webb|
|Wednesday, 15 February 2012 03:34|
Reposted from Chris Webb's blog with the author's permission.
Over six years ago now I wrote what proved to be a very popular post here on my blog called “So, what is the UDM?”. It was written in response to the widespread confusion around the time of the release of Analysis Services 2005 about what the term “UDM” actually meant. In a sense “UDM” was just another name for an Analysis Services cube, but it also represented the nebulous concept of Analysis Services being a semantic layer suitable for all your reporting needs; however people often thought it was a new product that somehow replaced Analysis Services cubes and got themselves tied in all sorts of knots as a result. Thankfully, use of the term died out pretty quickly as everyone started referring to Analysis Services as, well, Analysis Services.
Fast forward to the present day and I can see a similar amount of confusion about the term “BI Semantic Model” or BISM for many of the same reasons. What is the BI Semantic Model exactly? It is… Analysis Services 2012 plus PowerPivot. Let’s be clear though: it is not just the new Analysis Services Tabular Model, although the term BISM is all too often used as if it did mean that. It’s not even a specific bit of software. Analysis Services 2012 consists of two parts, the Multidimensional Model which is the Analysis Services of cubes and dimensions that we already had in 2008 R2 and earlier versions, and the new Tabular model which is the Analysis Services of tables, relationships, in-memory storage and column store. BISM refers to both models plus PowerPivot, or rather it refers to the way that Analysis Services and PowerPivot can be used as a semantic layer on top of other data for reporting purposes.
So what’s the point of a term like BISM then if it doesn’t refer to something tangible? Why not just call Analysis Services “Analysis Services” and PowerPivot “PowerPivot”? Well there’s certainly some conceptual stuff going on here (as outlined in the Vision and Roadmap blog post) but just as we had with the term UDM I’d say there’s also some marketing-led obfuscation here as well, for three reasons:
Now I’m not going to suggest that there’s anything wrong with these marketing objectives – anything that sells more Analysis Services is good for me – or that the Tabular model is bad, or anything like that. All I want to do is suggest that in the SQL Server technical community we stop using the term BISM and instead refer to Analysis Services Multidimensional, Analysis Services Tabular and PowerPivot so we’re always clear about what we’re talking about in blog posts, articles, books and so on. I don’t think using the term BISM is useful in any technical context, just as the term UDM wasn’t in the past, because it is a blanket term for several different things. I also think that so many people are confused about what the term BISM actually means that it is becoming counter-productive to use it: people will not buy into the MS BI stack if they’re not really sure what it consists of.
What does everyone think about this?