As I get to see more Enterprise BI initiatives, it is becoming increasingly clear (atleast to me!) that when it comes to information dissemination, Hybrid Online Analytical Processing (HOLAP) is the way to go. Let me explain my position here.
As you might be aware, Relational (ROLAP), Multi-dimensional (MOLAP) and Hybrid OLAP (HOLAP) are the 3 modes of information delivery for BI systems. In an ROLAP environment, the data is stored in a relational structure and is accessed through a semantic layer (usually!). MOLAP on the other hand stores data in proprietary format providing the notion of a multi-dimensional cube to users. HOLAP combines the power of both ROLAP and MOLAP systems and with the rapid improvements made by BI tool vendors, seems to have finally arrived on the scene.
In my mind, the argument for subscribing to the HOLAP paradigm goes back to the “classic” article
by Ralph Kimball on different types of fact table grains. According to him, there are 3 types of fact tables – Transaction grained, Periodic snapshot, Accumulating snapshot and that atleast 2 of them are required to model a business situation completely. From an analytical standpoint, this means that operational data has to be analyzed along with summarized data (snapshots) for business users to take informed decisions.
Traditionally, the BI world has handled this problem in 2 ways:
1) Build everything on the ROLAP architecture. Handle the summarization either on the fly or thro’ summarized reporting tables at the database level. This is not a very elegant solution as everybody in the organization (even those analysts working with summarized information) gets penalized for the slow performance of SQL queries issued against the relational database through the semantic layer.
2) Profile users and segregate operational analysts from strategic analysts. Operational users are provided ROLAP tools while business users working primarily with summarized information are provided their “own” cubes (MOLAP) for high-performance analytics.
Both solutions are rapidly becoming passé. In many organizations now, business users wants to look at summarized information and based on what they see, needs the facility to drill down to granular level information. A good example is the case of analyzing Ledger information (Income statement & Balance Sheet) and then drilling down to Journal entries as required. All this drilling down has to happen through a common interface – either an independent BI Tool or an enterprise portal with an underlying OLAP engine.
This is the world of HOLAP and it is here to stay. The technology improvement that is making this possible is the relatively new wonder-kid, XMLA (XML for Analysis). More about XMLA in my subsequent posts.
As an example of HOLAP architecture, you can take a look at this link
to understand the integration of Essbase cubes (MOLAP at its best) with OBIEE (Siebel Analytics – ROLAP platform) to provide a common semantic model for end-user analytics.
Information Nugget: If you are interested in Oracle Business Intelligence, please do stop by at http://www.rittmanmead.com/blog/ to read his blogs. The articles are very informative and thoroughly practical.
Thanks for reading. Please do share your thoughts.