Schema in Data ware House

Star Schema

The star schema (sometimes referenced as star join schema) is the simplest style of data ware house schema. The star schema consists of a few fact tables (possibly only one, justifying the name) referencing any number of dimension table. The star schema is considered an important special case of the snow flake schema.

Snowflake schema

A snowflake schema is a logical arrangement of tables in a multidimensional database such that the entity relationship diagram resembles a snowflake in shape. Closely related to the star schema, the snowflake schema is represented by centralized fact table which are connected to multiple dimensions. In the snowflake schema, however, dimensions are normalized into multiple related tables whereas the star schema's dimensions are denormalized with each dimension being represented by a single table. When the dimensions of a snowflake schema are elaborate, having multiple levels of relationships, and where child tables have multiple parent tables ("forks in the road"), a complex snowflake shape starts to emerge. The "snowflaking" effect only affects the dimension tables and not the fact tables.

Constellation schema

For each star schema or snowflake schema it is possible to construct a fact constellation schema.
This schema is more complex than star or snowflake architecture, which is because it contains multiple fact tables. This allows dimension tables to be shared amongst many fact tables.
That solution is very flexible, however it may be hard to manage and support.

The main disadvantage of the fact constellation schema is a more complicated design because many variants of aggregation must be considered.

In a fact constellation schema, different fact tables are explicitly assigned to the dimensions, which are for given facts relevant. This may be useful in cases when some facts are associated with a given dimension level and other facts with a deeper dimension level.
Use of that model should be reasonable when for example, there is a sales fact table (with details down to the exact date and invoice header id) and a fact table with sales forecast which is calculated based on month, client id and product id.
In that case using two different fact tables on a different level of grouping is realized through a fact constellation model.

Ratan N. Tata

Ratan N Tata has been the Chairman of Tata Sons, the promoter company of the Tata group, since 1991. He is also the Chairman of the major Tata companies, including Tata Motors, Tata Steel, Tata Consultancy Services, Tata Power, Tata Tea, Tata Chemicals, Indian Hotels and Tata Teleservices. During his tenure, the group’s revenues have grown nearly 12-fold. Mr Tata also serves on the board of directors of Fiat SpA and Alcoa. He is also on the international advisory boards of Mitsubishi Corporation, the American International Group, JP Morgan Chase and Rolls Royce. Mr Tata is associated with various organisations in India and overseas. He is the Chairman of two of the largest private-sector-promoted philanthropic trusts in India. He is a member of the Prime Minister’s Council on Trade and Industry, the National Hydrogen Energy Board, and the National Manufacturing Competitiveness Council. He is the president of the Court of the Indian Institute of Science and Chairman of the Council of management of the Tata Institute of Fundamental Research. He also serves on the UK Prime Minister’s Business Council for Britain and the International Advisory Council of Singapore’s Economic Development Board. He is also a member of the Global Business Council on HIV / Aids and the Programme Board of the Bill and Melinda Gates Foundation’s India Aids initiative. Mr Tata joined the Tata group in 1962. After serving in various companies, he was appointed director-in-charge of The National Radio and Electronics Company in 1971. In 1981 he was named Chairman of Tata Industries, the group’s other promoter company, where he was responsible for transforming it into a group strategy think-tank, and a promoter of new ventures in high technology businesses. Mr Tata received a BS degree in architecture from Cornell in 1962. He worked briefly with Jones and Emmons in Los Angeles before returning to India in late 1962. He completed the Advanced Management Program at Harvard Business School in 1975. The Government of India honoured Mr Tata with its second-highest civilian award, the Padma Vibhushan, in 2008. He has also received honorary doctorates from Ohio State University, the Asian Institute of Technology, the University of Warwick and the Indian Institutes of Technology of Kharagpur and Madras, and an honorary fellowship from the London School of Economics.