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Advantage of the COURSE
If a data exploration environment is to be useful it must fulfill the following criteria:
• complex questions can be asked with a simple SQL query
• different questions imply very similar SQL query structure
• very different questions require very similar processing time to answer
• exploration can be done from any computer anywhere
The goal is that a business expert can sit down at a Web browser, use a sequence of forms to specify a query, and get a result back in an amount of time that seems reasonable.
It will be impossible to achieve this with our standard OLTP data models. Answering a particular question may require JOINing in four or five extra tables, which could result in a 10,000-fold increase in processing time. Even if a novice user could be guided to specifying a 7-way JOIN from among 600 tables, that person would have no way of understanding or predicting query processing time. Finally there is the question of whether you want novices querying your OLTP tables. If they are only typing SELECTs they might not be doing too much long-term harm but the short-term processing load might result in a system that feels crippled.
It is time to study data warehousing.
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