OLAP Analysis: Workflow
To prepare data for use with the Pentaho/Jaspersoft OLAP Analysis (and Reporting, to a certain extent) client tools, you should follow this basic workflow :
Design a Star or Snowflake Schema
The entire process starts with a data warehouse. The end result should be data model in the star or snowflake schema pattern. You don’t have to worry too much about getting the model exactly right on your first try. Just cover all of your anticipated business needs; part of the process is coming back to the data warehouse design step and making changes to your initial data model after you’ve discovered what your operational needs are.
Populate the Star/Snowflake Schema
Once your data model is designed, the next step is to populate it with actual data, thereby creating your data warehouse. We can use Pentaho Data Integration or Talend for ETL.
Build a Mondrian Schema
Now that your initial data warehouse project is complete, you must build a Mondrian schema to organize and describe it in terms that Pentaho/Jasper Analysis can understand. This is also accomplished through Pentaho Data Integration by using the Agile BI plugin. Just connect to your data warehouse and auto-populate your schema with the Modeler graphical interface. Alternatively, you can use Schema Workbench to create an analysis schema through a manual process.
At this point you should have a multi-dimensional data structure with an appropriate metadata layer. You can now start using Pentaho Analyzer, Jasper Ad-hoc and JPivot to drill down into your data and see if your first attempt at data modeling was successful. In all likelihood, it will need some adjustment, so take note of all of the schema limitations that you’re unhappy with during this initial testing phase.
Do not be concerned with performance issues at this time – just concentrate on the completeness and comprehensiveness of the data model.
Adjust and Repeat Until Satisfied
Use the notes you took during the testing phase to redesign your data warehouse and Mondrian schema appropriately. Adjust hierarchies and relational measure aggregation methods. Create virtual cubes for analyzing multiple fact tables by conforming dimensions. Re-test the new implementation and continue to refine the data model until it matches your business needs perfectly.
Test for Performance
Once you’re satisfied with the design and implementation of your data model, you should try to find performance problems and address them by tuning your data warehouse database, and by creating aggregation tables. The testing can only be reasonably done by hand, using Pentaho Analyzer, Jaspersoft Ad-hoc or JPivot. Take note of all of the measures that take an unreasonably long time to calculate. Also, enable SQL logging and locate slow-performing queries, and build indexes for optimizing query performance.
Create Aggregation Tables
Using your notes as a guide, create aggregation tables using Pentaho Aggregation Designer or talend to store frequently computed analysis views. Re-test and create new aggregation tables as necessary.
If you are working with a relatively small data warehouse or a limited number of dimensions, you may not have a real need for aggregation tables. However, be aware of the possibility that performance issues may come up in the future.
Check in with your users occasionally to see if they have any particular concerns about the speed of their BI content.
Deploy to Production
Your data warehouse and Mondrian schema have been created, tested, and refined. You’re now ready to put it all into production. OLAP reports help users to do multi-dimensional and cross functional analysis, slice and dice, drill-up and drill-through the data. It gives power in the hands of business users to generate ad-hoc reports and get better insight of their business and and make better decisions based on OLAP analysis.
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