Concerns in using data warehouse

• Extracting, cleaning and loading data could be time consuming.
• Data warehousing project scope might increase.
• Problems with compatibility with systems already in place e.g. transaction processing system.
• Providing training to end-users, who end up not using the data warehouse.
• Security could develop into a serious issue, especially if the data warehouse is web accessible.
• A data warehouse is a HIGH maintenance system.

Advantages of using data warehouse

There are many advantages to using a data warehouse, some of them are:
• Enhances end-user access to a wide variety of data.
• Increases data consistency.
• Increases productivity and decreases computing costs.
• Is able to combine data from different sources, in one place.
• It provides an infrastructure that could support changes to data and replication of the changed data back into the operational systems.

Different methods of storing data in a data warehouse

All data warehouses store their data grouped together by subject areas that reflect the general usage of the data (Customer, Product, Finance etc.) The general principle used in the majority of data warehouses is that data is stored at its most elemental level for use in reporting and information analysis. Within this generic intent, there are two primary approaches to organising the data in a data warehouse.
The first is using a "dimensional" approach. In this style, information is stored as "facts" which are numeric or text data that capture specific data about a single transaction or event, and "dimensions" which contain reference information that allows each transaction or event to be classified in various ways. As an example, a sales transaction would be broken up into facts such as the number of products ordered, and the price paid, and dimensions such as date, customer, product, geographical location and sales person.

Optional Components

In addition, the following components also exist in some data warehouses:
1. Dependent Data Marts: A dependent data mart is a physical database (either on the same hardware as the data warehouse or on a separate hardware platform) that receives all its information from the data warehouse. The purpose of a Data Mart is to provide a sub-set of the data warehouse's data for a specific purpose or to a specific sub-group of the organisation.
2. Logical Data Marts: A logical data mart is a filtered view of the main data warehouse but does not physically exist as a separate data copy. This approach to data marts delivers the same benefits but has the additional advantages of not requiring additional (costly) disk space and it is always as current with data as the main data warehouse.

Operations

Data warehouse operations comprises of the processes of loading, manipulating and extracting data from the data warehouse. Operations also covers user management, security, capacity management and related functions.