DATA WAREHOUSING

DATA WAREHOUSING

Data Warehousing is the process of constructing and using the data warehouse. The data warehouse is constructed by integrating the data from multiple heterogeneous sources. This data warehouse supports analytical reporting, structured and/or ad hoc queries and decision making. Data Warehousing involves data cleaning, data integration and data consolidations.

Integrating Heterogeneous Databases

To integrate heterogeneous databases we have the two approaches as follows:

1.     Query Driven Approach

2.     Update Driven Approach

Query Driven Approach

This is the traditional approach to integrate heterogeneous databases. This approach was used to build wrappers and integrators on the top of multiple heterogeneous databases. These integrators are also known as mediators.

PROCESS OF QUERY DRIVEN APPROACH:

·         When the query is issued to a client side, a metadata dictionary translates the query into the queries appropriate for the individual heterogeneous site involved.

·         Now these queries are mapped and sent to the local query processor.

·         The results from heterogeneous sites are integrated into a global answer set.

DISADVANTAGES

·         The Query Driven Approach needs complex integration and filtering processes.

·         This approach is very inefficient.

·         This approach is very expensive for frequent queries.

·         This approach is also very expensive for queries that require aggregations.

Update Driven Approach

We are provided with the alternative approach to traditional approach. Today's Data Warehouse system follows update driven approach rather than the traditional approach discussed earlier. In Update driven approach the information from multiple heterogeneous sources is integrated in advance and stored in a warehouse. This information is available for direct querying and analysis.

ADVANTAGES

This approach has the following advantages:

·         This approach provides high performance.

·         The data are copied, processed, integrated, annotated, summarized and restructured in semantic data store in advance.

·         Query processing does not require interface with the processing at local sources.