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. Read More about Hybrid OLAP
