Wednesday, 11 February 2015

Data Warehousing Technical Round Interview Questions and Answers (Page 8)

Below are some important Data Warehouse interview questions which are asked in most MNC company interviews for beginners or professionals.

71. What are the steps involved in Database Startup?

Start an instance, Mount the Database and Open the Database.

72. Which parameter specified in the DEFAULT STORAGE clause of CREATE TABLESPACE cannot be altered after creating the table space?
All the default storage parameters defined for the table space can be changed using the ALTER TABLESPACE command. When objects are created their INITIAL and MINEXTENS
values cannot be changed.

73. What is On-line Redo Log?
The On-line Redo Log is a set of tow or more on-line redo files that record all committed changes made to the database. Whenever a transaction is committed, the corresponding redo entries temporarily stores in redo log buffers of the SGA are written to an on-line redo log file by the background process LGWR. The on-line redo log files are used in cyclical fashion.

74. What is Log Switch?
The point at which ORACLE ends writing to one online redo log file and begins writing to another is called a log switch.

75. What is Dimensional Modelling?
Dimensional Modelling is a design concept used by many data warehouse designers to build their data warehouse. 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 measurements i.e., the dimensions on which the facts are calculated.

76. What are the difference between Snow flake and Star Schema? What are situations where Snow flake Schema is better than Star Schema to use and when the opposite is true?
Star schema contains the dimension tables mapped around one or more fact tables. It is a renormalized model and no need to use complicated joins. Also queries results fast.Snowflake schema: It is the normalized form of Star schema. It contains in-depth joins, because the tables are split in to many pieces. We can easily do modification directly in the tables. We have to use complicated joins, since we have more tables.There will be some delay in processing the query.

77. What is a cube in data warehousing concept?
Cubes are logical representation of multidimensional data. The edge of the cube contains dimension members and the body of the cube contains data values.

78. What are the differences between star and snowflake schema?
Star schema: A single fact table with N number of DimensionSnowflake schema: Any dimensions with extended dimensions are known as snowflake schema.

79. What are Data Marts?
A data mart is a collection of tables focused on specific business group/department. It may have multi-dimensional or normalized. Data marts are usually built from a bigger data warehouse or from operational data.

80. What is the data type of the surrogate key?
There is no data type for a Surrogate Key. Requirement of a surrogate Key: UNIQUE Recommended data type of a Surrogate key is NUMERIC.
More Questions & Answers :-
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