Wednesday, 11 February 2015

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

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

91. Why fact table is in normal form?
The fact table consists of the Index keys of the dimension/look up tables and the measures. So whenever we have the keys in a table. That it implies that the table is in the normal form.

92. What is Difference between E-R Modeling and Dimensional Modeling?
Basic difference is E-R modeling will have logical and physical model. Dimensional model will have only physical model. E-R modeling is used for normalizing the OLTP database design.Dimensional modeling is used for de-normalizing the ROLAP/MOLAP design.

93. What is conformed fact?
Conformed dimensions are the dimensions, which can be used across multiple Data Marts in combination with multiple facts tables accordingly

94. What are the methodologies of Data Warehousing?
Every company has methodology of their own. However, to name a few SDLC Methodology, AIM methodology is standard used.

95. What is BUS Schema?
BUS Schema is composed of a master suite of confirmed dimension and standardized definition if facts.

96. What is Data warehousing Hierarchy?
Hierarchies are logical structures that use ordered levels as a means of organizing data. A hierarchy can be used to define data aggregation. For example, in a time dimension, a hierarchy might aggregate data from the month level to the quarter level to the year level. A hierarchy can also be used to define a navigational drill path and to establish a family structure.Within a hierarchy, each level is logically connected to the levels above and below it. Data values at lower levels aggregate
into the data values at higher levels. A dimension can be composed of more than one hierarchy. For example, in the product dimension, there might be two hierarchies--one for product categories and one for product suppliers.Dimension hierarchies also group levels from general to granular. Query tools use hierarchies to enable you to drill down into your data to view different levels of granularity. This is one of the key benefits of a data warehouse.When designing hierarchies, you must consider
the relationships in business structures. Hierarchies impose a family structure on dimension values. For a particular level value, a value at the next higher level is its parent, and values at the next lower level are its children. These familial relationships enable analysts to access data quickly.

97. What are data validation strategies for data mart validation after loading process?
Data validation is to make sure that the loaded data is accurate and meets the business requirements. Strategies are different methods followed to meet the validation requirements.

98. What are the data types present in BO? What happens if we implement view in the designer n report?
Three different data types: Dimensions, Measure, and DetailView is nothing but an alias and it can be used to resolve the loops in the universe.

99. What is surrogate key? Where we use it? Explain with examples.
Surrogate key is a substitution for the natural primary key.It is just a unique identifier or number for each row that can be used for the primary key to the table.
The only requirement for a surrogate primary key is that it is unique for each row in the table.
Data warehouses typically use a surrogate, (also known as artificial or identity key), key for the dimension tables primary keys. They can use Info sequence generator, or Oracle sequence, or SQL Server Identity values for the surrogate key.
It is useful because the natural primary key (i.e. Customer Number in Customer table) can change and this makes updates more difficult.
Some tables have columns such as AIRPORT_NAME OR CITY_NAME which are stated as the primary keys (according to the business users) but ,not only can these change, indexing on a numerical value is probably better and you could consider creating a surrogate key called, say, AIRPORT_ID. This would be internal to the system and as far as the client is concerned, you may display only the AIRPORT_NAME.

100. What is a linked cube?
Linked cube in which a sub-set of the data can be analyzed into detail. The linking ensures that the data in the cubes remain consistent.
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