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General Datawarehousing Interview Questions & Answers - Learning Mode

General Datawarehousing Interview Questions & Answers - Learning Mode

Data warehousing is the process of constructing and using a data warehouse. A data warehouse is constructed by integrating data from multiple heterogeneous sources that support analytical reporting, structured and/or ad hoc queries, and decision making. Data warehousing is the process of constructing and using a data warehouse. A data warehouse is constructed by integrating data from multiple heterogeneous sources that support analytical reporting, structured and/or ad hoc queries, and decision making.

Try General Datawarehousing Interview Questions & Answers - Exam Mode

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General Datawarehousing Interview Questions & Answers - Learning Mode
Try General Datawarehousing Interview Questions & Answers - Exam Mode
Question: What type of Indexing mechanism do we need to use for a typical datawarehouse?

Answer: On the fact table it is best to use bitmap indexes. Dimension tables can use bitmap and/or the other types of clustered/non-clustered, unique/non-unique indexes.

To my knowledge, SQLServer does not support bitmap indexes. Only Oracle supports bitmaps. Source:
Question: What are Semi-additive and factless facts and in which scenario will you use such kinds of fact tables?

Answer: Snapshot facts are semi-additive, while we maintain aggregated facts we go for semi-additive.

EX: Average daily balance

A fact table without numeric fact columns is called factless fact table.

Ex: Promotion Facts

While maintain the promotion values of the transaction (ex: product samples) because this table doesn’t contain any measures.

Submitted by Srikanth M ( creku @ yahoo . com ) Source:
Question: What is VLDB?

Answer: VLDB stands for Very Large DataBase.

It is an environment or storage space managed by a relational database management system (RDBMS) consisting of vast quantities of information.

Submitted By: Francis C. ( xxchen74 @ hotmail . com )


VLDB doesn’t refer to size of database or vast amount of information stored. It refers to the window of opportunity to take back up the database.

Window of opportunity refers to the time of interval and Source:
Question: What is the Difference between OLTP and OLAP?

Answer: Main Differences between OLTP and OLAP are:-

1. User and System Orientation

OLTP: customer-oriented, used for data analysis and querying by clerks, clients and IT professionals.

OLAP: market-oriented, used for data analysis by knowledge workers( managers, executives, analysis).

2. Data Contents

OLTP: manages current data, very detail-oriented.

OLAP: manages large amounts of historical data, provides facilities for summarization and aggregation, Source:
Question: What is a level of Granularity of a fact table?

Answer: Level of granularity means level of detail that you put into the fact table in a data warehouse. For example: Based on design you can decide to put the sales data in each transaction. Now, level of granularity would mean what detail are you willing to put for each transactional fact. Product sales with respect to each minute or you want to aggregate it upto minute and put that data. Source:
Question: What are the Different methods of loading Dimension tables?

Answer: Conventional Load:
Before loading the data, all the Table constraints will be checked against the data.

Direct load:(Faster Loading)
All the Constraints will be disabled. Data will be loaded directly.Later the data will be checked against the table constraints and the bad data won't be indexed.
Question: What is ODS?

Answer: 1. ODS means Operational Data Store.

Submitted by Francis C. ( xxchen74 @ hotmail . com )

2. A collection of operation or bases data that is extracted from operation databases and standardized, cleansed, consolidated, transformed, and loaded into an enterprise data architecture. An ODS is used to support data mining of operational data, or as the store for base data that is summarized for a data warehouse. The ODS may also be used to audit the data warehouse to assure summarized an Source:
Question: What is a general purpose scheduling tool?

Answer: The basic purpose of the scheduling tool in a DW Application is to stream line the flow of data from Source To Target at specific time or based on some condition.
Question: What is SCD1 , SCD2 , SCD3?

Answer: SCD Stands for Slowly changing dimensions.

SCD1: only maintained updated values.

Ex: a customer address modified we update existing record with new address.

SCD2: maintaining historical information and current information by using

A) Effective Date

B) Versions

C) Flags

or combination of these

SCD3: by adding new columns to target table we maintain historical information and curr Source:
Question: What are Aggregate tables?

Answer: Aggregate table contains the summary of existing warehouse data which is grouped to certain levels of dimensions.Retrieving the required data from the actual table, which have millions of records will take more time and also affects the server performance.To avoid this we can aggregate the table to certain required level and can use it.This tables reduces the load in the database server and increases the performance of the query and can retrieve the result very fastly. Source:
Question: Define pre-emptive and non-pre-emptive.

Answer: Premptive means taken as a measure against something possible, anticipated, or feared; preventive; deterrent: a preemptive tactic against a ruthless business rival.

Non Pre-emptive is the exact opposite to Pre-emptive.No such preventive measures has been taken. Source:
Question: Why are OLTP database designs not generally a good idea for a Data Warehouse?

Answer: Since in OLTP,tables are normalised and hence query response will be slow for end user and OLTP doesnot contain years of data and hence cannot be analysed.

Submitted by Venkat Mothukuri ( Source:
Question: What is Normalization, First Normal Form, Second Normal Form , Third Normal Form?

Answer: 1.Normalization is process for assigning attributes to entities?Reducesdata redundancies?Helps eliminate data anomalies?Produces controlledredundancies to link tables

2.Normalization is the analysis offunctional dependency between attributes / data items of userviews􀁺It reduces a complex user view to a set of small andstable subgroups of fields / relations

1NF:Repeating groups must beeliminated, Dependencies can be identified, All key attributesdefined,No repeating groups Source:
Question: What is ER Diagram?

Answer: The Entity-Relationship (ER) model was originally proposed by Peter in 1976 [Chen76] as a way to unify the network and relational database views.

Simply stated the ER model is a conceptual data model that views the real world as entities and relationships. A basic component of the model is the Entity-Relationship diagram which is used to visually represents data objects.

Since Chen wrote his paper the model has been extended and today it is commonly used for database design F Source:
Question: What is data mining?

Answer: Data mining is a process of extracting hidden trends within a datawarehouse. For example an insurance dataware house can be used to mine data for the most high risk people to insure in a certain geographial area. Source:
Question: Name some of modeling tools available in the Market?

Answer: These tools are used for Data/dimension modeling

1. Oracle Designer
2. ERWin (Entity Relationship for windows)
3. Informatica (Cubes/Dimensions)
4. Embarcadero
5. Power Designer Sybase Source:
Question: What does level of Granularity of a fact table signify?

Answer: Granularity
The first step in designing a fact table is to
determine the granularity of the fact table. By
granularity, we mean the lowest level of information
that will be stored in the fact table. This
constitutes two steps:

Determine which dimensions will be included.
Determine where along the hierarchy of each dimension
the information will be kept.
The determining factors usually goes back to the

Submitted by Avinash J ( Source:
Question: How are the Dimension tables designed?

Answer: Most dimension tables are designed using Normalization principles upto 2NF. In some instances they are further normalized to 3NF.

Find where data for this dimension are located.

Figure out how to extract this data.

Determine how to maintain changes to this dimension (see more on this in the next section).

Change fact table and DW population routines. Source:
Question: What are non-additive facts?

Answer: Non-Additive: Non-additive facts are facts that cannot
be summed up for any of the dimensions present in the
fact table.

Submitted by Avinash J ( Source:
Question: Explain the advanatages of RAID 1, 1/0, and 5. What type of RAID setup would you put your TX logs.

Answer: Transaction logs write sequentially and don't need to be read at all. The ideal is to have each on RAID 1/0 because it has much better write performance than RAID 5.

RAID 1 is also better for TX logs and costs less than 1/0 to implement. It has a tad less reliability and performance is a little worse generally speaking.

RAID 5 is best for data generally because of cost and the fact it provides great read capability.

Submitted by Nimisha Bansal ( Source:

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