Which aspect is NOT a function of OLAP?

OLAP, or Online Analytical Processing, is primarily focused on analyzing large volumes of data and facilitating complex queries that help in decision-making. The key functions of OLAP include data retrieval, which allows users to access and interrogate data stored in databases, and data analysis, where users can perform multidimensional analysis to gain insights into trends and patterns.

Data storage is also relevant, as OLAP systems often rely on large data warehouses or data marts to aggregate and organize the data to enable efficient querying and reporting. However, data purification, which involves cleaning and filtering data to ensure its quality before it is analyzed, is not a function typically associated with OLAP. This task is generally handled during the data preparation process, often in the ETL (Extract, Transform, Load) phase before data reaches the OLAP system.

Thus, the reason the choice of data purification is correct as "not a function of OLAP" lies in the distinction between preprocessing data and the analytical capabilities that OLAP provides.