Data Warehousing Questions

Q:

What is Uniform Data Access Integration?

Answer

- UDAI places the data in the source systems.


- A set of views are defined for providing access the unified view to the clients / customers.


- Zero latency of data can be propagated from the source system.


- The generated consolidated data need not require separate storage space.


- Data history and version management is limited and applied only to the similar type of data.


- Accessing to the user data overloads on the source systems.

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Q:

What is Cascade and Drill Through? What is the difference between them?

Answer

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.

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Q:

What is Data warehousing?

Answer

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. 

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Q:

Explain the difference between star and snowflake schemas.

Answer

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.

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Q:

What is Bit Mapped Index?

Answer

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. 

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Q:

What is Dimensional Modeling?

Answer

Dimensional modeling is often used in Data warehousing. In simpler words it is a rational or consistent design technique used to build a data warehouse. DM uses facts and dimensions of a warehouse for its design. A snow and star flake schema represent data modeling.

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Q:

What are the factors that are addressed to integrate data?

Answer

Following are the data integration factors:


- Sub set of the available data should be optimal. 


- Noise/distortion estimation levels because of sensory/processing conditions at the time of data collection.


- Accuracy, spatial and spectral resolution of data.


- Data formats, storage and retrieval mechanisms.


- Efficiency of computation for integrating data sets to reach the goals.

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Q:

What is the difference between view and materialized view?

Answer

View:


- Tail raid data representation is provided by a view to access data from its table.


- It has logical structure can not occupy space.


- Changes get affected in corresponding tables.


 


Materialized view


- Pre calculated data persists in materialized view.


- It has physical data space occupation.


- Changes will not get affected in corresponding tables.

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