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General Datawarehousing Interview Questions & Answers - Learning Mode
COOLINTERVIEW.COM DATA WAREHOUSING INTERVIEW QUESTIONS GENERAL DATAWAREHOUSING INTERVIEW QUESTIONS 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: CoolInterview.com
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: CoolInterview.com
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: CoolInterview.com
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: CoolInterview.com
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: CoolInterview.com
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: CoolInterview.com
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: CoolInterview.com
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.
Source: CoolInterview.com
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: CoolInterview.com
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 (VMothukuri@covansys.com) Source: CoolInterview.com
Question: What are conformed dimensions?

Answer: Conformed dimensions mean the exact same thing with every possible fact table to which they are joined
Ex:Date Dimensions is connected all facts like Sales facts,Inventory facts..etc

Submitted by Srikanth M (creku @ yahoo . com ) Source: CoolInterview.com
Question: What are conformed dimensions?

Answer: Conformed dimentions are dimensions which are common to the cubes.(cubes are the schemas contains facts and dimension tables)

Consider Cube-1 contains F1,D1,D2,D3 and Cube-2 contains F2,D1,D2,D4 are the Facts and Dimensions
here D1,D2 are the Conformed Dimensions Source: CoolInterview.com
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.
Source: CoolInterview.com
Question: Why should you put your data warehouse on a different system than your OLTP system?

Answer: A OLTP system is basically " data oriented " (ER model) and not " Subject oriented "(Dimensional Model) .That is why we design a separate system that will have a subject oriented OLAP system...

Moreover if a complex querry is fired on a OLTP system will cause a heavy overhead on the OLTP server that will affect the daytoday business directly.

Submitted by Vijayaraghavan.C ( chakra_vijay@yahoo.com )

_____________

The loading of a warehouse will likely consume a lot Source: CoolInterview.com
Question: What is Dimensional Modelling? Why is it important ?

Answer: Dimensional Modelling is a design concept used by many data warehouse desginers to build thier datawarehouse. In this design model all the data is stored in two types of tables - Facts table and Dimension table. Fact table contains the facts/measurements of the business and the dimension table contains the context of measuremnets ie, the dimensions on which the facts are calculated.

Why is Data Modeling Important?
---------------------------------------

Data modeling is probabl Source: CoolInterview.com
Question: What is a lookup table?

Answer: A lookUp table is the one which is used when updating a warehouse. When the lookup is placed on the target table (fact table / warehouse) based upon the primary key of the target, it just updates the table by allowing only new records or updated records based on the lookup condition.

Submitted by Siva Kumar (siva.athuru@gmail.com) Source: CoolInterview.com
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: CoolInterview.com
Question: Define and expansion of ssl.

Answer: The Secure Sockets Layer (SSL) is a commonly-used protocol for managing the security of a message transmission on the Internet. SSL has recently been succeeded by Transport Layer Security (TLS), which is based on SSL. SSL uses a program layer located between the Internet's Hypertext Transfer Protocol (HTTP) and Transport Control Protocol (TCP) layers. SSL is included as part of both the Microsoft and Netscape browsers and most Web server products. Developed by Netscape, SSL also gained the Source: CoolInterview.com
Question: What is a dimension table?

Answer: A dimensional table is a collection of hierarchies and categories along which the user can drill down and drill up. it contains only the textual attributes. Source: CoolInterview.com
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: CoolInterview.com

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