Data Warehousing Questions

The primary keys of entity tables are the foreign keys of dimension tables.

The Primary keys of fact dimensional table are the foreign keys of fact tablels.

At the time of updating the data warehouse, a lookup table is used. When placed on the fact table or warehouse based upon the primary key of the target, the update is takes place only by allowing new records or updated records depending upon the condition of lookup.

The materialized views are aggregate tables. It contains summarized data. For example, to generate sales reports on weekly or monthly or yearly basis instead of daily basis of an application, the date values are aggregated into week values, week values are aggregated into month values and month values into year values. To perform this process aggregate function is used.

Fact is key performance indicator to analyze the business.From the additive values, which are used to analyse the business by using report generation. Dimension is used to analyze the fact, are the non-additive ( text format) values, Which are used to drill down reports.Without dimension there is no meaning for fact. Measure is the quantity of data we create to process.

Cascade:

- Cascade process involves taking values from various other prompts.

- The result is a single report.

- The result is used when a criteria is to be implemented.

Drill Through:

- Drill Through process is implemented when navigation from summary to detailed information.

- Drill Through has a parent and a child report.

- Data of another report can be seen based on the current details of data.

Data warehousing is a process of repository of electronic data of an organization. For the purpose of reporting and analysis, data warehousing is used. The essence concept of data warehousing is to provide data flow of architectural model from operational system to decision support environments. 

Star schema: A highly de-normalized technique. A star schema has one fact table and is associated with numerous dimensions table and depicts a star.

Snow flake schema: The normalized principles applied star schema is known as Snow flake schema. Every dimension table is associated with sub dimension table.

Differences:

- A dimension table will not have parent table in star schema, whereas snow flake schemas have one or more parent tables.

- The dimensional table itself consists of hierarchies of dimensions in star schema, where as hierarchies are split into different tables in snow flake schema. The drilling down data from top most hierarchies to the lowermost hierarchies can be done.

Bitmap indexes make use of bit arrays (bitmaps) to answer queries by performing bitwise logical operations.

Bitmap indexes are useful in the data warehousing applications.

Bitmap indexes have a significant space and performance advantage over other structures for such data.

Tables that have less number of insert or update operations can be good candidates.

The advantages of Bitmap indexes are:

   - They have a highly compressed structure, making them fast to read.

   - Their structure makes it possible for the system to combine multiple indexes together so that they can      access the underlying table faster.

The Disadvantage of Bitmap indexes is:

  - The overhead on maintaining them is enormous.