tailieunhanh - Data Warehousing Fundamentals A Comprehensive Guide for IT Professionals phần 8

Arsenal của OLAP. Bất kỳ hệ thống OLAP không có phân tích đa chiều là hoàn toàn vô dụng. Vì vậy, cố gắng để có được một hình ảnh rõ ràng của cơ sở cung cấp trong hệ thống OLAP để phân tích chiều. Chúng ta hãy bắt đầu với một giản đồ STAR đơn giản. Giản đồ STAR này có ba khía cạnh kinh doanh, cụ thể là, sản phẩm, thời gian, và lưu trữ. Bảng thực tế có doanh số bán hàng. | 354 OLAP IN THE DATA WAREHOUSE arsenal of OLAP. Any OLAP system devoid of multidimensional analysis is utterly useless. So try to get a clear picture of the facility provided in OLAP systems for dimensional analysis. Let us begin with a simple STAR schema. This STAR schema has three business dimensions namely product time and store. The fact table contains sales. Please see Figure 15-5 showing the schema and a three-dimensional representation of the model as a cube with products on the X-axis time on the Y-axis and stores on the Z-axis. What are the values represented along each axis For example in the STAR schema time is one of the dimensions and month is one of the attributes of the time dimension. Values of this attribute month are represented on the Y-axis. Similarly values of the attributes product name and store name are represented on the other two axes. This schema with just three business dimensions does not even look like a star. Nevertheless it is a dimensional model. From the attributes of the dimension tables pick the attribute product name from the product dimension month from the time dimension and store name from the store dimension. Now look at the cube representing the values of these attributes along the primary edges of the physical cube. Go further and visualize the sales for coats in the month of January at the New York store to be at the intersection of the three lines representing the product coats month January and store New York. If you are displaying the data for sales along these three dimensions on a spreadsheet the columns may display the product names the rows the months and pages the data along the third dimension of store names. See Figure 15-6 showing a screen display of a page of this three-dimensional data. The page displayed on the screen shows a slice of the cube. Now look at the cube and move along a slice or plane passing through the point on the Z-axis representing store New York. The intersection points on this slice or .