Data Warehouse

What is a Data Warehouse?

• A pool of data combined from databases across an enterprise to be the source for decision making.
• A repository of current and historical data of potential interest to managers throughout the organization.
• A subject-oriented, integrated, time-variant, nonvolatile collection of data in support of management’s decision-making process.


How does a Data Warehouse differ from a database?

Most operational databases have a product orientation and are tuned to handle transactions that update the database.

What is a Data Mart?

A small warehouse designed for a strategic business unit or a department and is a subset of the datawarehouse.

What is the Data Warehousing process?

Data for the data warehouse is imported from various internal and external resources and is cleaned and organized in a manner consistent with the organization’s needs. After the data is populated in the data warehouse, data mart can be loaded for a specific area or department. Alternatively data mart can be created first and then integrated into an Enterprise Data Warehouse (EDW) if needed.

What are the major components of a data warehouse?

• Data sources
• Data extraction and transformation
• Data loading
• Comprehensive database
• Metadata
• Middleware tools.
 
What are the three steps of the ETL process?

1. Extraction – reading data from one or more databases. Typically all the input data are written to a set of staging tables.

2. Transformation – converting the extracted data from its previous form into the form in which it needs to be so that it can be placed into a data warehouse or simply another database. Transformation occurs by using rules or lookup tables or by combining the data with other data. Any data quality issues pertaining to the source files need to be corrected before the data are loaded to the data warehouse.

3. Load – putting data into the data warehouse.

Why is the ETL process so important for data warehousing effort?

ETL is extremely important for data integration and for providing clean quality data for data warehouse. Quality data becomes a strategic asses for a company.