What is Fact Constellation Schema?
A Fact constellation means two or more fact tables sharing one or more dimensions. It is also called Galaxy schema.
Fact Constellation Schema describes a logical structure of data warehouse or data mart. Fact Constellation Schema can design with a collection of de-normalized FACT, Shared, and Conformed Dimension tables.
Fact Constellation Schema is a sophisticated database design that is difficult to summarize information. Fact Constellation Schema can implement between aggregate Fact tables or decompose a complex Fact table into independent simplex Fact tables.
Example: A fact constellation schema is shown in the figure below.
This schema defines two fact tables, sales, and shipping. Sales are treated along four dimensions, namely, time, item, branch, and location. The schema contains a fact table for sales that includes keys to each of the four dimensions, along with two measures: Rupee_sold and units_sold. The shipping table has five dimensions, or keys: item_key, time_key, shipper_key, from_location, and to_location, and two measures: Rupee_cost and units_shipped.
The primary disadvantage of the fact constellation schema is that it is a more challenging design because many variants for specific kinds of aggregation must be considered and selected.
Data Warehouse Applications
The application areas of the data warehouse are:
It deals with querying, statistical analysis, and reporting via tables, charts, or graphs. Nowadays, information processing of data warehouse is to construct a low cost, web-based accessing tools typically integrated with web browsers.
It supports various online analytical processing such as drill-down, roll-up, and pivoting. The historical data is being processed in both summarized and detailed format.
OLAP is implemented on data warehouses or data marts. The primary objective of OLAP is to support ad-hoc querying needed for support DSS. The multidimensional view of data is fundamental to the OLAP application. OLAP is an operational view, not a data structure or schema. The complex nature of OLAP applications requires a multidimensional view of the data.
It helps in the analysis of hidden design and association, constructing scientific models, operating classification and prediction, and performing the mining results using visualization tools.
Data mining is the technique of designing essential new correlations, patterns, and trends by changing through high amounts of a record save in repositories, using pattern recognition technologies as well as statistical and mathematical techniques.
It is the phase of selection, exploration, and modeling of huge quantities of information to determine regularities or relations that are at first unknown to access precise and useful results for the owner of the database.
It is the process of inspection and analysis, by automatic or semi-automatic means, of large quantities of records to discover meaningful patterns and rules.
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