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Data Warehousing in Microsoft SQL Server 2008

What Data Warehousing Is Not

Much confusion exists in the literature and among practitioners because many terms are regularly conflated with data warehousing, even now when the maturity of the field should preclude this. A charitable view is that this was at least understandable in the past when the field was evolving rapidly in theory, practice, and product. But today, there ought to be more clarity, precision, and common understanding. In furtherance of this, we feel it is worth asserting that there are worthwhile distinctions still represented by certain overused and misused terms. This section provides a brief summary of some of these terms.

OLAP

The term online analytical processing, or OLAP, was coined by Dr. E. F. Codd (the originator of the relational model) in 1994 to distinguish a set of properties that analytical applications should satisfy (in contrast with his famous 1985 publication of “12 Rules” that a relational database management system should satisfy; see http://en.wikipedia.org/wiki/Codd’s_12_rules). The term was intended to draw distinctions between the at-the-time well-known properties of OLTP applications and the less-well-defined properties of analytical applications. It is probably most valuable simply for emphasizing that such a distinction should be made. Today the term can be understood also as referring to a response to the limitations of spreadsheet-based approaches. While not strictly part of the definition, as a practical matter, cube-based technology is now usually associated with OLAP.

An OLAP application often, although not of necessity, draws its data from some form of star schema. The various OLAP tools on the market today form a spectrum in the degree to which they require a recognizable star schema as their data source. At one end, some tools can deliver OLAP functionality, with relatively simple calculations, from just about any data source with any organization, while at the other end are tools that can use only cubes (a data structure designed to facilitate fast analysis, further described in Chapter 15) as their data source (and hopefully can fully exploit their power). A data warehouse is very helpful as the source anywhere on this spectrum and is a virtual necessity on the cube-oriented end of it.

In the context of SQL Server, Analysis Services is Microsoft’s full-featured OLAP engine; it is covered in detail in Chapter 15 through Chapter 18.

Data Mining

The traditional way of extracting information from data requires a skilled analyst with a deep understanding of the enterprise who formulates ad hoc queries, the answers to which he or she think would be interesting—for example, “What was the impact of last month’s sales promotion on sales?” or “Which stores in the top 10 by sales this year were also in the top 10 by sales last year?” In effect, the analyst forms hypotheses of cause and effect and then tests them against the data. To be effective, this rather hit-or-miss style of information discovery requires tools that permit easily formulating the queries and fast response so that the analyst can maintain his or her train of thought. OLAP technology is ideally suited for this.

In contrast, data mining is an approach in which correlations that might exist in a data set are automatically “discovered” using specialized data models and statistical algorithms. Because it is automated, it is more thorough in finding correlations, and it is unaffected by the prejudices and blind spots that an analyst would have using an ad hoc approach. The analyst still needs to evaluate each correlation found to determine whether it is meaningful or merely correlative, however.

In principle, data mining does not require a data warehouse for its source data. However, a well-crafted data warehouse with clean data could be an ideal source. The intended analysis and the allowable latency also affect whether a data warehouse as an analysis source is feasible. For example, in detecting credit card fraud, is the data warehouse updated often enough to be useful?

Starting with SQL Server 2000, Microsoft has invested much effort in giving SQL Server Analysis Services data mining capabilities that are much easier for relative nonspecialists to use than what has previously been available on the market. These capabilities are covered in detail in Chapter 18.

Business Intelligence

The term business intelligence (BI), coined by analyst Howard Dressner in 1989, has turned out to be quite popular. Today it is applied in so many contexts that you would be right to wonder whether it distinguishes anything anymore. Some argue that it doesn’t, but we think that it still does. It is unfortunate that the business in BI obscures the fact that BI can be valuable in any enterprise, not just the for-profit ones implied by the B. So as suggested earlier, think enterprise intelligence when you hear business intelligence.

The most important thing to be clear about is that BI, properly understood, is not about any particular technology—although its implementation certainly depends on technology. BI is fundamentally a management approach and philosophy. Like most good ideas, its basic premise sounds so obvious when stated that it hardly seems worth noting: management decisions should be based on facts, not on educated guesswork, politics, or other subjective bases. Of course, management of an enterprise has always been based at some level on objective information—accounting being the most elemental form. But in the past, such objective measures, especially at the enterprise level, were at a summary level, produced infrequently (if periodically), rigidly structured, and incapable of easily revealing the detail from which they were derived.

BI aims to change all this by ensuring that information is accurate, reliable, updated as frequently as necessary, and readily accessible to whoever needs it, regardless of their level in the organization. One focus of BI is on the technologies required to achieve these goals, which generally include some form of data warehouse—hence the association. But the technology focus, especially on user interfaces (UIs), tends to receive disproportionate attention. An equally important focus should be on the vision of fact-based decision making that is supported by senior management and influences the way the enterprise will be run.

Initially, BI often faced significant resistance in the enterprise. If knowledge is power, losing control of knowledge feels like (and often is) losing power. BI threatened this with its emphasis on making information available to a much broader audience. Fortunately by now, the value of BI is recognized in most enterprises.

Last, we must mention that historically, many BI projects and their supporting data warehouse implementations have overpromised and underdelivered, giving BI a bad reputation for being expensive and risky. As a result, some are beginning to rethink the necessity of creating a data warehouse to support BI and instead are using existing reports and other existing data sources directly as BI sources. While this approach has its appeal, only time will tell whether it becomes an important theme in BI implementation.

Dashboards and Scorecards

The terms dashboard and scorecard are often used synonymously. They both represent information graphically, summarizing it with various elements showing relative magnitudes, trends, and other meaningful relationships. But they are not synonymous.

Dashboards

A dashboard, like its automobile namesake, displays measures without the context of related goals. It has a “just the facts” tactical orientation and is updated as often as necessary for the (typically) operational process that it supports. It is more generic than a proper scorecard in that it can display anything (including a scorecard). Figure 14-7 shows a typical dashboard.

Figure 14-7

Figure 14-7. A typical dashboard

Scorecards

A scorecard displays base measures in the context of related goals, objectives, or target measures and provides at-a-glance visual cues as to whether each such base measure is lagging, achieving, or surpassing its goal measure. Obviously, therefore, a scorecard is not possible unless such goal measures exist in addition to the base measures. A strategy must be devised for such goal measures to exist. It follows that a scorecard is strategic, whereas a dashboard is tactical and operational.

The term key performance indicator (KPI) is closely associated with scorecards. The traffic light and trend indicators in Figure 14-8 are KPIs. A KPI encapsulates a measure, a related goal measure, a calculation about the relationship of the two, and a graphic that expresses a “good or bad” indication based on the calculation.

Figure 14-8

Figure 14-8. A typical scorecard

Goal measures are usually not defined at lower levels of detail. Consider the difference in grain between Actual and Plan measures—the former derive from individual transactions, while the latter are created at a much more summarized level, at least in the Time dimension. For this reason, scorecards tend to report at a more summarized level than dashboards, which is consistent with their strategic vs. tactical orientation. This in turn also means that changes occur more slowly, so scorecards are usually refreshed less often than dashboards. In a financial scorecard like the one shown in Figure 14-8, an Actual vs. Plan KPI exhibits all these principles and is seen as a traffic light in the Plan columns. Notice the Trend indicator, which is also a KPI that uses some calculation between prior-period Actual and Plan values.

Since SQL Server 2005, Analysis Services provides KPI objects that can be stored in cubes. They can be consumed and displayed by Microsoft Office Excel 2007, Microsoft Office SharePoint Server, and Microsoft Performance Point, each of which also allows creating and storing KPIs within its respective environment.

Performance Management

Performance management is a relatively recent term that is a particular flavor of BI but rates its own discussion because of its currency in the literature and market today as a distinct entity. Performance management implies BI—but the converse is not true, because BI is the more general term. As noted earlier, BI’s techniques can be focused in many different directions. Performance management is a specific application of BI. It is first about establishing organizational goals and objectives and ways of measuring progress toward meeting them—often using BI techniques to help determine what those goals and measures should be. Once these goals are established, it is then about gathering past, current, and projected performance, explicitly measuring these against the established goals, and widely disseminating how well goals are being met. This is usually achieved in the form of scorecards, which are again facilitated by BI tools and techniques.

The Balanced Scorecard (BSC) is a well-known example of performance management that predates the term. It is worth becoming familiar with the BSC approach, not least because it can help you better understand the factors driving enterprise strategy, and how to ensure that the strategy is enacted.