When a user analyzes the measurements along a business dimension, the user usually would like to see the numbers first in summary and then at various levels of detail. What' the user does here is to traverse the hierarchical levels of a business dimension for getting the details at various levels. For example, the user first sees the total sales for the entire year. Then the user moves down to the level of quarters and looks at the sales by individual quarters. After this, the user moves down further to the level of individual months to look at monthly numbers. What we notice here is that the hierarchy of the time dimension consists of the levels of year, quarter, and month. The dimension hierarchies are the paths for drilling down or rolling up in our analysis.
Within each major business dimension there are categories of data elements that can also be useful for analysis. In the time dimension, you may have a data element to indicate whether a particular day is a holiday. This data clement would enable you to analyze by holidays and see how sales on holidays compare with sales on other days. Similarly, in the product dimension, you may want to analyze by type of package. The package type is one such data clement within the product dimension. The holiday nag in the time dimension and the package type in the product dimension do not necessarily indicate hierarchical levels in these dimensions. Such data elements within the business dimension may he called categories.
Hierarchies and categories are included in the information packages for each dimension. Let us go back to the two examples in the previous section and find out which hierarchical levels and categories must be included for the dimensions. Let us examine the product dimension. Let us examine product is the basic automobile. Therefore, we include the data elements relevant to product as hierarchies and categories. These would be model name, model year, package styling, product line, pi %.duct category, exterior color, interior color, and first model year. Looking at the other business dimensions for the auto sales analysis, we summarize the hierarchies and categories for each dimension as follows:
Product:- Model name, model year, package styling, product line, product category, exterior color, interior color, first model year
Dealer:- Dealer name, city, state, single brand nag, date first operation
Customer demographics:- Age, gender, income range, marital status, household sue, Veil IC Ics owned, home value, own or rent
Payment method:- ' Finance type, term in months, interest rate, agent
Time:- Date, month, quarter, year, day of week, day of month, season, holiday flag
Let us go back to the hotel occupancy analysis. We I' ' included three business dimensions. Let us list the possible hierarchies and category the three dimensions.
Hotel:- Hotel line, branch name, branch code, region, address, city, state, Zip Code, manager, construction year, renovation year
Room Type:- Room type, room size, number of bed, types of beds, maximum occupants, suite, refrigerator, kitchenette
Time:- Date, day of month, day of week, month, quartet, year, holiday flag