Data Mining and Warehousing - 2

Data Mining and Warehousing - 2

OLAP Systems and Data Warehouse Hardware

OLAP Systems: Basic Concepts:

OLAP, or Online Analytical Processing, is a technology designed to support complex data analysis and reporting tasks. It enables users to interactively explore and analyze multidimensional data, gain insights, and make informed decisions. OLAP systems are optimized for analytical tasks rather than transactional processing.

What Is OLAP? OLAP Defined | NetSuite

Differences between OLAP and OLTP (Online Transaction Processing) Systems:

OLTP (Online Transaction Processing):

  • Purpose: OLTP systems manage day-to-day operational tasks, such as order processing, inventory management, and customer transactions.

  • Data Structure: OLTP systems use normalized data structures to minimize data redundancy and ensure data integrity.

  • Transactions: OLTP systems prioritize fast and reliable transaction processing, focusing on data modification, insertion, and retrieval.

  • Database Size: OLTP databases tend to be larger due to the volume of transactions they handle.

  • User Load: OLTP systems support a high number of concurrent users, each performing simple, routine tasks.

OLAP (Online Analytical Processing):

Online Analytical Processing (OLAP) Explanied | AltexSoft

  • Purpose: OLAP systems support complex data analysis, reporting, and decision-making tasks by providing multidimensional views of data.

  • Data Structure: OLAP systems use denormalized or partially normalized structures to optimize query performance.

  • Queries: OLAP systems prioritize complex queries that involve aggregations, grouping, and slicing and dicing of data.

  • Database Size: OLAP databases are smaller compared to OLTP databases, as they store aggregated and summarized data.

  • User Load: OLAP systems handle a smaller number of users performing more complex analytical tasks.

How OLAP Systems Facilitate Complex Analysis and Reporting:

  • Multidimensional Views: OLAP systems organize data in dimensions and hierarchies, allowing users to view data from different angles and levels of detail.

  • Aggregation: OLAP systems can quickly aggregate data to provide summary information, enabling high-level insights.

  • Slicing and Dicing: Users can "slice" data by selecting specific dimensions and "dice" it by drilling down into hierarchies, revealing detailed information.

  • Drill-Down and Roll-Up: OLAP systems support drilling down to see detailed data and rolling up to see higher-level summaries.

  • Pivoting: Users can pivot data to change the orientation of their analysis and focus on different aspects of the data.

  • Complex Calculations: OLAP systems often support custom calculations, ratios, and measures, enhancing analysis accuracy.

  • Interactive Analysis: Users can interactively explore data, making iterative queries to find insights and trends.

OLAP Queries:

Exploring the Types of Queries Supported by OLAP Systems:

OLAP systems support various types of queries that allow users to interact with multidimensional data and gain insights. These queries are designed to facilitate analytical exploration rather than simple data retrieval. Some of the key types of OLAP queries include:

  • Drill-Down: Going from higher-level aggregated data to more detailed data. For example, going from annual sales to monthly sales.

  • Roll-Up: Opposite of drill-down, aggregating data from a lower level to a higher level. For example, aggregating monthly sales to quarterly sales.

  • Slice: Selecting a single value along one dimension to view a "slice" of data. For example, viewing sales data for a specific product category.

  • Dice: Selecting specific values along multiple dimensions to view a subset of data. For example, viewing sales data for a specific product category and a particular time period.

  • Pivot: Changing the orientation of the data to focus on different dimensions. For example, pivoting data to view sales by region rather than by product.

Drilling Down, Rolling Up, Slicing, and Dicing Operations:


  • Drilling down involves moving from a higher-level summary to more detailed data.

  • It helps users understand the components that contribute to an aggregate value.

  • For example, going from annual sales to quarterly sales and then to monthly sales.


  • Rolling up is the opposite of drilling down, where detailed data is aggregated to a higher level.

  • It allows users to see summarized views and trends.

  • For example, aggregating monthly sales to quarterly or annual sales.


  • Slicing involves selecting a single value along one dimension to view a subset of data.

  • It provides insights into specific aspects of the data.

  • For example, viewing sales data for a particular product category.


  • Dicing involves selecting specific values along multiple dimensions to create a subcube.

  • It allows users to focus on a specific subset of data for analysis.

  • For example, viewing sales data for a specific product category and a certain time period.

Examples of Using OLAP Queries to Extract Insights from Multidimensional Data:

  • Example 1: Sales Analysis by Region and Product:

    • Slice: View sales data for the "Electronics" category.

    • Dice: Focus on sales data for "Electronics" in the "Western" region.

  • Example 2: Time Analysis of Monthly Revenue:

    • Drill-Down: Go from annual revenue to quarterly revenue to monthly revenue.

    • Roll-Up: Aggregate monthly revenue to quarterly or annual revenue.

  • Example 3: Product Performance Analysis:

    • Drill-Down: Go from total revenue to revenue by product category to revenue by specific product.

    • Roll-Up: Aggregate product-level revenue to category-level or total revenue.

Types of OLAP Servers:

MOLAP (Multidimensional OLAP): Storing Data in Multidimensional Arrays:

What is MOLAP (Multidimensional OLAP) in Data Warehouse?

  • MOLAP systems store data in a multidimensional format, optimized for fast querying and analysis.

  • Data is pre-aggregated, and organized in a cube-like structure, with dimensions as axes and measures in the cells.

  • Efficient for complex analytical operations like slicing, dicing, drilling down, and rolling up.

  • Offers fast query performance due to the pre-aggregated nature of data.

  • Popular MOLAP solutions include Microsoft Analysis Services and IBM Cognos TM1.

ROLAP (Relational OLAP): Using Relational Databases to Store Multidimensional Data:

  • ROLAP systems utilize relational databases to store data in a tabular format.

  • Data is normalized, with dimensions and facts stored in separate relational tables.

  • Generates SQL queries to aggregate data on the fly, providing flexibility in handling large datasets.

  • Suitable for scenarios where data changes frequently or when data volumes are extensive.

  • Allows integration with existing relational database systems.

  • Examples of ROLAP tools include Microsoft SQL Server Analysis Services (Tabular model) and Oracle OLAP.

HOLAP (Hybrid OLAP): Combining Aspects of Both MOLAP and ROLAP:

  • HOLAP systems attempt to combine the strengths of MOLAP and ROLAP.

  • They allow data to be stored in both multidimensional arrays and relational tables.

  • Aggregations are precomputed for better performance, while some detailed data is stored relationally.

  • Offers a balance between query performance and storage efficiency.

  • Addresses limitations of MOLAP and ROLAP by providing a more flexible storage approach.

  • Provides a way to handle large datasets and dynamic data changes effectively.

OLAP Operations:

Consolidation: Aggregating Data to Higher Levels of Granularity:

  • Purpose: Consolidation involves summarizing detailed data to higher levels of granularity.

  • Use Case: For instance, aggregating daily sales data to monthly or yearly totals.

  • Benefits: Provides a broader view of trends and patterns, making it easier to identify overarching insights.

Drill-Through: Navigating from Summarized Data to Detailed Data:

  • Purpose: Drill-through allows users to access the underlying detailed data from a summarized view.

  • Use Case: Starting with a total sales figure and drilling through to see individual sales transactions.

  • Benefits: Enables investigation of specific data points behind summary values for better context and understanding.

Pivoting: Rotating Data Axes to View Information from Different Perspectives:

  • Purpose: Pivoting involves changing the orientation of data dimensions to explore different viewpoints.

  • Use Case: Swapping rows and columns to view sales by product instead of sales by region.

  • Benefits: Offers new insights by presenting data in alternative formats, aiding in data exploration.

Slicing and Dicing: Focusing on Specific Subsets of Data:

  • Slicing: Selecting a single value along one dimension to view a "slice" of data.

    • For example, viewing sales data for a specific product category.
  • Dicing: Selecting specific values along multiple dimensions to view a subset of data.

    • For example, viewing sales data for a specific product category and a certain time period.
  • Benefits: Allows users to narrow down their analysis to specific areas of interest.

Data Warehouse Hardware and Operational Design:

Ensuring Security in Data Warehousing:

Access Control and User Authentication:

  • Access Control: Implement strict access control mechanisms to ensure that only authorized users can access specific data.

  • User Authentication: Require users to authenticate using secure methods like passwords, multi-factor authentication, or biometrics.

Encryption Techniques to Protect Sensitive Data:

  • Data Encryption: Encrypt data at rest and during transmission to protect it from unauthorized access.

  • Encryption Algorithms: Use strong encryption algorithms and protocols to ensure data confidentiality.

Backup and Recovery:

Importance of Regular Data Backups:

  • Data loss can occur due to hardware failures, software glitches, human errors, or disasters.

  • Regular data backups ensure that a recent and reliable copy of data is available for recovery.

Strategies for Data Recovery in Case of Failures or Disasters:

Backup Strategies:

  • Full Backup: Copies all data, ensuring comprehensive recovery but consuming more storage.

  • Incremental Backup: Only backs up changes made since the last backup, conserving storage space but requiring multiple backups for complete recovery.

  • Differential Backup: Backs up changes since the last full backup, striking a balance between storage and recovery time.

Recovery Techniques:

  • Point-in-Time Recovery: Restore data to a specific point in time, useful for recovering from data corruption or accidental deletion.

  • Disaster Recovery: Maintain off-site backups to recover data in case of catastrophic events affecting the primary data centre.

Testing Backup and Recovery Plans:

  • Regularly test backup and recovery processes to ensure they work effectively.

  • Simulate various failure scenarios to identify potential weaknesses in the recovery plan.

Off-Site Backup and Cloud Storage:

  • Store backups in a secure off-site location to protect against physical damage or local disasters.

  • Cloud storage can provide scalable and secure backup options, offering data redundancy.