Aggregate navigation

Aggregate Navigation

First and foremost , it is important to define 'Aggregate Navigation since it a vague term that can be confused with other disciplines or subject matters . Aggregate navigation , as used in information technology , is a technique that enables DBAs (Database Administrators to optimize performance by storing aggregate values in the database without requiring end-users to know about the existence of those aggregates (Kimball , 1995 . It is a 'capability ' that changes the architecture of all end-user applications . An aggregate navigator on the other hand , is a software component that intercepts SQL

(Structured Query Language ) and transforms it to use the best available aggregates (McKenna

The Star schema

To fully understand the application of 'Aggregate Navigation ' it is necessary to discuss some concepts such as the star schema and the data warehouse . A star schema is a set of tables in a relational database that has been designed according to the principles of dimensional modelling (Adamson , 2006 ,

. 2 . This approach to data warehouse design was popularized by Ralph Kimball in the 1990s

W .H . Inmon defines data warehouse as a subject oriented , integrated time-variant , and non-volatile collection of data in support of management decisions (cited in Kirpekar , 1996 ,

. 3 . A data warehouse system serves a different purpose from an operational system . The data warehouse supports the evaluation of the business process , while the operational system supports the execution of the process . Their distinct purposes are reflected in contrasting usage pros , which in turn suggest that different principles will guide their design (Adamson , 2006 ,

. 4 . Data warehouse systems are concerned about s such as monthly trends in s , comparison in sales per quarter efficacy of marketing promotions , and the identification of the best customers . Within the data warehouse , information is neither created nor modified since interaction takes place exclusively through queries that receive data . The table below illustrates the difference between an operational system and a data warehouse system

Operational System Data Warehouse

Also known as Transaction System Analytic System

Purpose Execution of business process Measurement of business process

Primary Interaction Style Insert , Update , Query , Delete Query

Scope of Interaction Individual transaction Aggregated transactions

Query Patterns Predictable and stable Unpredictable and changing

Temporal Focus Current Current and historic

Design Principle Third normal form (3NF ) Dimensional design (star schema

Figure 1 (Source : Adamson , 2006 ,

.4

The significance of dimensional modelling is that its principles address the unique requirements of data warehouse systems . A star schema design is optimized for queries that access large volumes of data , rather than individual transactions . It also supports the maintenance of historic data , even as the operational systems change or delete information (Adamson , 2006 ,

. 4

Figure 2 (Source : Kimball , 1996

The figure above illustrates a base star schema with a central fact table surrounded by four dimension tables

Figure 3 (Source : Kimball , 1996

The figure above shows an aggregated star schema derived from figure 2 by aggregating the product dimension up to the category level . The aggregate schema provides a partially aggregated summarization...