Wednesday 11 February 2015

Data Warehouse frequently asked interview Questions and Answers (Page 9)

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

81. What are Fact, Dimension, and Measure?

Fact is key performance indicator to analyze the business. Dimension is used to analyze the fact. Without dimension there is no meaning for fact.

82. What are the different types of data warehousing?
Types of data warehousing are:
1. Enterprise Data warehousing
2. ODS (Operational Data Store)
3. Data Mart

83. What do you mean by static and local variable?
Static variable is not created on function stack but is created in the initialized data segment and hence the variable can be shared across the multiple call of the same function. Usage of static variables within a function is not thread safe.On the other hand, local variable or auto variable is created on function stack and valid only in the context of the function call and is not shared across function calls.

84. What is a source qualifier?
When you add a relational or a flat file source definition to a mapping, you need to connect it to a Source Qualifier transformation. The Source Qualifier represents the rows that the Informatica Server reads when it executes a session.

85. What is the data type of the surrogate key?
Data type of the surrogate key is integer, numeric, or number.

86. What are the steps to build the data warehouse?
Gathering business requirements>>Identifying Sources>>Identifying Facts>>Defining Dimensions>>Define Attributes>>Redefine Dimensions / Attributes>>Organize Attribute
Hierarchy>>Define Relationship>>Assign Unique Identifiers

87. What is the advantages data mining over traditional approaches?
Data Mining is used for the estimation of future. For example, if we take a company/business organization, by using the concept of Data Mining, we can predict the future of business in terms of Revenue (or) Employees (or) Customers (or) Orders etc.Traditional approaches use simple algorithms for estimating the future. However, it does not give accurate results when compared to Data Mining.

88. What is the difference between view and materialized view?
View - store the SQL statement in the database and let you use it as a table. Every time you access the view, the SQL statement executes. Materialized view - stores the results of the SQL in table form in the database. SQL statement only executes once and after that every time you run the query, the stored result set is used. Pros include quick query results.

89. What is the main difference between Inmon and Kimball philosophies of data warehousing?
Both differed in the concept of building the data warehouse.According to Kimball, Kimball views data warehousing as a constituency of data marts. Data marts are focused on delivering business objectives for departments in the organization. And the data warehouse is a conformed dimension of the data marts. Hence, a unified view of the enterprise can be obtained from the dimension modeling on a local departmental level.Inmon beliefs in creating a data warehouse on a subject-by-subject area
basis. Hence, the development of the data warehouse can start with data from the online store. Other subject areas can be added to the data warehouse as their needs arise. Point-of-sale (POS) data can be added later if management decides it is necessary.

90. What is junk dimension? What is the difference between junk dimension and degenerated dimension?
Junk dimension: Grouping of Random flags and text attributes in a dimension and moving them to a separate sub dimension. Degenerate Dimension: Keeping the control information on Fact table ex: Consider a Dimension table with fields like order number and order line number and have 1:1 relationship with Fact table, In this case this dimension is removed and the order information will be directly store
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