1.     What do you mean by Data Warehousing?

A data warehouse is the chief repository of an organization’s historical data, its corporate memory. It holds the raw material for management’s decision support system. The data analyst can perform difficult queries and analysis, including data mining, on the information without slowing down the operational systems. Data warehousing collection of data isdesigned to support the management decision making. Data warehouses contain aextensive variety of heterogeneous data that present a clear picture of business conditions at a single instance in time.

2. Explain the  fundamental stages of Data Warehousing?

Offline OperationalDatabases

Data warehouses in this initial stage are established by simply copying the database of an operational system to an off-line server where processing load of reporting does not effect on the operational system’s performance.

Offline Data Warehouse

In this stage,Data warehouses are updated on a regular time interval (daily or weekly or monthly) from operational systems and the data is stored in integrated reporting-oriented data structure.

Real Time DataWarehouse

At this stage Data Warehouses are updated on a transaction or an event basis ( It is done every time an operational system performs any transaction).

Integrated Data Warehouse

At this stage Data warehouses are used to produce activity or transactions which are passed back into the operational systems.

3. What is Dimensional Modeling

This concept involves two types of tables. It is different from the 3rd NF. It uses Facts table containing the measurements of the business and Dimension table containing the contextof the measurements.

4. What is Fact table?

It contains measurements of business processes. It contains foreign keys for the dimension tables.

5. What is Dimension table

Dimension table contains textual attributes of measurements which stored in the fact tables. Dimensional table is a collection of hierarchies, logic andcategories which can be used for user to traverse in hierarchy nodes.

6. Different methods of loading Dimension tables

There are 2 different methods to load data in dimension tables.
Conventional or Slow – Here all the keys and constraints are validated against the data before it is loaded.
Direct or Fast – In this case allthe keys and constraints are disabled before data is loaded. Once the data is loaded, then it is validated against all the keys and constraints. If it is found invalid it is not included in the index and all future processes.

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