Data Warehouse is a subject-oriented information database, specially designed for reports and business analysis preparation to support decision-making within an organisation. It is built on the basis of database management systems and decision support systems. Data that enters the data store is usually read-only.
Data from an OLTP system is copied to a data warehouse in such a way that, during the construction of reports and OLAP-analysis, the resources of the transaction system are not used and its stability is not violated. There are two options for updating the data in the repository:
Complete data update in a repository. First old data is deleted and new data is then downloaded. The process occurs with a certain periodicity, while the data actuality may lag somewhat behind the OLTP-system;
Incremental update – only that data that has changed within the OLTP system is updated.
The principles of storage organisation
- Problem-objective orientation. Data is combined into categories and stored in accordance with the areas it describes, not with the applications it uses.
- Integration. Data is combined so as to meet all the requirements of an enterprise as a whole, and not the sole function of the business.
- Uncorrectable. Data in a warehouse is not created: that is, it comes from external sources and is not corrected or deleted.
- Dependence on time. Data in the repository is accurate and correct only if it is tied to a certain period or point in time.
Data Processes
Data sources can be:
- Traditional systems of operation registration
- Individual documents
- Datasets
Data Operations:
- Extraction – moving information from data sources to a separate database, bringing them into a single format.
- Transformation – preparing information for storage in an optimum form for implementation of a request necessary for decision-making.
- Loading – putting data into a repository. This is performed atomically by adding new facts or adjusting existing ones.
- Analysis – OLAP, Data Mining, summary reports.
- Presentation of the results of analysis.