tailieunhanh - Hướng dẫn học Microsoft SQL Server 2008 part 153

Phân cấp và mối quan hệ thuộc tính Khi triển khai, mỗi thuộc tính không cụ thể vô hiệu hóa sẽ trở thành một hệ thống phân cấp thuộc tính để duyệt web và truy vấn. Các hệ thống phân cấp thuộc tính nói chung bao gồm hai cấp: cấp Tất cả, đại diện cho tất cả các giá trị của các thuộc tính, và một mức độ được đặt tên theo các thuộc tính tự liệt kê mỗi giá trị riêng. | PartX Business Intelligence 1482 Change the KeyColumns property for the currently selected attribute by clicking on the current value and then clicking the ellipses to launch the Key Columns dialog. The left pane of the Key Columns dialog shows each of the current key members. Use the left and right arrows to build a key in the right pane as shown in Figure 71-4. FIGURE 71-4 The Key Columns dialog Likewise add or change an attribute s NameColumn binding by clicking the ellipses to invoke the Name Column dialog. Highlight the column that contains the desired value. Hierarchies and attribute relationships Once deployed each attribute not specifically disabled becomes an attribute hierarchy for browsing and querying. The attribute hierarchy generally consists of two levels the All level which represents all possible values of the attribute and a level named after the attribute itself that lists each value individually. The Hierarchies and Levels pane of the Dimension Designer enables the creation of user hierarchies which define drill-down paths by organizing attributes into multiple levels. For example Building Multidimensional Cubes with Analysis Services 71 Figure 71-3 shows a user hierarchy that first presents the browser with a list of countries which can be expanded into a list of states then cities and so on. Ultimately the user will experience the dimension as some combination of attribute and user hierarchies. One of the most important practices to optimize cube performance is the careful construction of user hierarchies in conjunction with attribute relationships. This follows from how Analysis Services pre-calculates data summaries called aggregations to speed query performance. For example totals by year or month might be pre-calculated along the time dimension. To understand attribute relationships consider a simple time dimension with attributes for year quarter month and day with day relating to the fact table key attribute . By .