Why do people not report by Month in the Gregorian calendar?

1. The number of days is different in each calendar month.
2. The week and month cannot be aligned.  The number of weekends is different in each calendar month.
3. The number of working days is different in each calendar month.  It ends up that the number of days in each quarter is also different.
4. The period closing day will fall into different days in each period.  The accounting department prefers always close the period by a given day in a week, such as Wednesday or Friday.

13 Period Calendar

I will discuss the following topics:

• What is the 13 period calendar?
• Who uses the 13 period calendar?
• How is it different from the 4-4-5 calendar?

Data Warehouse Basics

Here is a link to my Data Warehouse Basics presentation slides. I explain what is a data warehouse, what is characteristics of a data warehouse, and what the data warehouse deployment looks like.

A good OBIEE web demo from New York City’s City Wide Performance Reporting

New York City now enables the public to monitor the city’s performance by making the OBIEE based dashboard and report online.

Here is the link to their CPR (City Wide Performance Reporting) site : http://www.nyc.gov/html/ops/cpr/html/home/home.shtml

Database Tuning - drop unused indexes

Index is very useful during query, especially in data warehouse.   However, it adds the overhead in the storage and ETL process.

I found an excellent article about how to monitor  the index usage in Oralce.   You should periodically run the index monitoring process and pro-actively drop those un-used indexes.

Bitmap Index - when to use it?

I will cover how Bitmap index work, when to use it and how to use it in this article.

How does it work?

The bitmap index stores the column values in bits. Each bit represents a single value. For example, the gender column has two possible values: Male and Female. three bit will be used in the bitmap to capture the index on the gender column. A good example can be seen in reference 1. So the more distinct value is, the more space is required to store the bitmap.

Internally, the database engine, like Oracle, uses a map function to converts the bit location to the distinct value. (See reference #2) Many bitmap indexes can be used together since database can merge it, so this can improve the response time. (See Reference #3 for the example of merging the index on Marital Status and Region)

When to use it?