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An Introduction to on-Line Analytical Processing (olap)

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An Introduction to OLAP

Multidimensional Terminology and Technology


What is OLAP? ______________________________________________________________________ 2

What is Multidimensional Data? _________________________________________________________ 3

Consolidation: The Key to Consistently Fast Response _______________________________________ 5

Simple Hierarchies Within Dimensions ____________________________________________________ 7

Variables ___________________________________________________________________________ 9

Vector Arithmetic ____________________________________________________________________ 10

n-Dimensional Databases _____________________________________________________________ 10

Practical Limitations on Database Size___________________________________________________ 12

Time-Series Data Type _______________________________________________________________ 12

Sparse Data________________________________________________________________________ 14

All Dimensions are Not Created Equal ___________________________________________________ 15

Multiple Hierarchies and Classes within Dimensions ________________________________________ 16

Drilling to Relational Data _____________________________________________________________ 17

Security and Robustness______________________________________________________________ 18

"MDSQL" Multidimensional Query Language ______________________________________________ 19

Conclusion_________________________________________________________________________ 20

What is OLAP?

OLAP stands for "On-Line Analytical Processing." In contrast to the more familiar OLTP ("On-Line

Transaction Processing"), OLAP describes a class of technologies that are designed for live ad hoc data

access and analysis. While transaction processing generally relies solely on relational databases, OLAP

has become synonymous with multidimensional views of business data. These multidimensional views

are supported by multidimensional database technology. These multidimensional views provide the

technical basis for the calculations and analysis required by Business Intelligence applications.

"Having an RDBMS doesn't mean instant decision-support nirvana. As enabling as RDBMSs have been

for users, they were never intended to provide powerful functions for data synthesis, analysis, and

consolidation (functions collectively known as multidimensional data analysis)."

- E. F. Codd, Computerworld

OLTP applications are characterized by many users creating, updating, or retrieving individual records.

Therefore, OLTP databases are optimized for transaction updating. OLAP applications are used by

analysts and managers who frequently want a higher-level aggregated view of the data, such as total

sales by product line, by region, and so forth. The OLAP database is usually updated in batch, often from

multiple sources, and provides a powerful analytical back-end to multiple user applications. Hence, OLAP

databases are optimized for analysis.

While relational databases are good at retrieving a small number of records quickly, they are not good at

retrieving a large number of records and summarizing them on the fly. Slow response time and inordinate

use of system resources are common characteristics of decision support applications built exclusively on

top of relational database technology. Because of the ease with which one can issue a "run-away SQL

query," many IS shops do not give users direct access to their relational databases.

Many of the problems that people attempt to solve with relational technology are actually

multidimensional in nature. For example, SQL queries to create summaries of product sales by region,

region sales by product, and so on, could involve scanning most if not all the records in a marketing

database and could take hours of processing. An OLAP server could handle these queries in a few


OLTP applications tend to deal with atomized "record-at-a-time" data, whereas OLAP applications usually

deal with summarized data. While OLTP applications generally do not require historical data, nearly every

OLAP application is concerned with viewing trends and therefore requires historical data. Accordingly,

OLAP databases need the ability to handle time-series data -- an attribute that will be discussed in detail

later in this paper. While OLTP applications and databases tend to be organized around specific

processes (such as order entry), OLAP applications tend to be "subject oriented," answering such

questions as "What products are selling well?" or "Where are my weakest sales offices?"

What is Multidimensional Data?

Relational databases are organized around a list of "records." Each record contains related information

that is organized into "fields." A typical example



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