DWH Interview Question and Answers

33. What are the functional requirements for a data warehouse?
  • A data warehouse must be able to support various types of information applications.
  • Decision support processing is the principle type of information application in a data warehouse, but the use of a data warehouse is not restricted to a decision support system.
  • It is possible that each information application has its own set of requirements in terms of data, the way that data is modeled, and the way it is used.
  • The data warehouse is where these applications get their "consolidated data."
  • A data warehouse must consolidate primitive data and it must provide all facilities to derive information from it, as required by the end–users.
  • Detailed primitive data is of prime importance, but data volumes tend to be big and users usually require information derived from the primitive data. Data in a data warehouse must be organized such that it can be analyzed or explored from different angles.
  • Analysis of the historical context (the time dimension) is of prime importance.
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34. What are an entity and attribute?
  • An entity represents a chunk of information. In relational databases, an entity often maps to a table.
  • An attribute is a component of an entity and helps define the uniqueness of the entity. In relational databases, an attribute maps to a column.
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35. What is a star schema?
  • A star schema is a set of tables comprised of a single, central fact table surrounded by de-normalized dimensions.
  • Each dimension is represented in a single table. Star schema implement dimensional data structures with de–normalized dimensions.
  • Snowflake schema is an alternative to star schema. A relational database schema for representing multidimensional data.
  • The data is stored in a central fact table, with one or more tables holding information on each dimension.
  • Dimensions have levels, and all levels are usually shown as columns in each dimension table.
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36. What is a snowflake schema?
  • A snowflake schema is a set of tables comprised of a single, central fact table surrounded by normalized dimension hierarchies.
  • Each dimension level is represented in a table.
  • Snowflake schema implements dimensional data structures with fully normalized dimensions. Star schema is an alternative to snowflake schema.
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