Better Star Schema Design Means Better Performance

  • by Gary Nolan, SAP BI Strategic Architect, Sapiex Associates LLC
  • September 1, 2004
Implementing an efficient star schema data model in your BW environment is critical if you expect your system to perform well. The author introduces you to the star schema and explains how it is used across the BW system and in the InfoCubes that underpin the system.
Key Concept
Data modeling in a BW system should reflect the decisions the BW team and other groups made during the earliest stages of implementation. Critical design elements, including ODS and InfoCube structures and load strategies, must be considered in the initial data model. Issues surrounding granularity, which is the lowest level of data BW users can access, must be resolved. If not, you may have to tweak your design — a potentially costly proposition after the system goes live.

The single biggest cause of poor performance during data loads and query retrieval is attributable to poor data modeling choices made early in the BW implementation process. Your initial data model reflects the most important decisions you will make during your BW project and includes such critical design elements as ODS/InfoCube structure, data load strategies, granularity, as well as your overall star schema design.

It is much more difficult to alter your data model after implementation, and most modeling revisions require a data dump and reload. Often, a data model that is sufficient for a lower volume begins to slow down and develop problems as the volume increases. It is imperative, therefore, that you pay ample attention at the beginning of a BW project to ensure the star schema design is optimal and can meet future challenges.

Data modeling is a critical, ongoing process because the data warehouse is evolving to accommodate data loads, new business developments, user behavior, etc. Because of an organization’s changing needs and ever- increasing data volume, you should revisit the data model from time to time to determine if the assumptions you made for the original model are still valid. It is likely that new requirements will be needed and data should be segregated differently by adding new ODS or InfoCube structures or new aggregates.

Gary Nolan

Gary Nolan is an SAP NetWeaver BW-certified consultant and author of Efficient SAP NetWeaver BW Implementation and Upgrade Guide and Efficient SAP NetWeaver BI Implementation and Project Management. Gary specializes in gathering and evaluating requirements, configuring SAP NetWeaver BW, and providing project management, performance management, and data architecture and data modeling expertise. A former platinum consultant with SAP America, Inc., Gary has more than 20 years of SAP experience, working with SAP NetWeaver BW since version 1.2B.

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