A Decision Support System (DSS) query on a very large table presents a special performance problem. If an ad-hoc query requires a table scan, every record in the table must be inspected, and this may take a long time. Where the query can be restricted to a single partition, or range of partitions, response time is dramatically reduced.
The performance of a DSS application can therefore be greatly improved by using a partition scan rather than a table scan.
(DSS) Decision support systems are defined as the class of warehouse system that deals with solving a semi-structured problem.
This means the task has a structured component as well as an unstructured component. In short, the unstructured component involves human intuition and requires human interaction with the DSS. The well-structured components of a DSS are the decision rules stored as the problem-processing system. The intuitive, or creative, component is left to the user.
The following represent some examples of semi-structured problems:
- Choosing a spouse. While there are many structured rules (I want someone of my religion, who is shorter than me), there is still the unstructured, unquantifiable component to the process of choosing a spouse.
- Choosing a site for a factory. This is a nonrecurring problem that has some structured components (cost of land, availability of workers, and so on), but there are many other unstructured components in this decision (i.e., quality of life).
- Choosing a stock portfolio. Here the structured rules are the amount of risk and the performance of stocks, but the choice of stocks for a portfolio requires human intuition.
Decision support technology recognizes that many tasks require human intuition. For example, the process of choosing a stock portfolio is a task which has both structured and intuitive components. Certainly, rules are associated with choosing a stock portfolio, such as diversification of the stocks and choosing an acceptable level of risk. These factors can be easily quantified and stored in a database system, allowing the user of the system to create what-if scenarios. However, just because a system has well-structured components does not guarantee that the entire decision process is well-structured.
One of the best ways to tell if a decision process is semi-structured is to ask the question:
Do people with the same level of knowledge demonstrate different levels of skill?