8-1數(shù)據(jù)倉庫與數(shù)據(jù)挖掘(存儲版)
【正文】 be formalized using distance metrics in several ways ? Group points into k sets (for a given k) such that the average distance of points from the centroid of their assigned group is minimized ? Centroid: point defined by taking average of coordinates in each dimension. ? Another metric: minimize average distance between every pair of points in a cluster ? Has been studied extensively in statistics, but on small data sets ? Data mining systems aim at clustering techniques that can handle very large data sets ? ., the Birch clustering algorithm (more shortly) 169。Silberschatz, Korth and Sudarshan Database System Concepts 6th Edition Regression ? Regression deals with the prediction of a value, rather than a class. ? Given values for a set of variables, X1, X2, …, X n, we wish to predict the value of a variable Y. ? One way is to infer coefficients a0, a1, a1, …, a n such that Y = a0 + a1 * X1 + a2 * X2 + … + an * Xn ? Finding such a linear polynomial is called linear regression. ? In general, the process of finding a curve that fits the data is also called curve fitting. ? The fit may only be approximate ? because of noise in the data, or ? because the relationship is not exactly a polynomial ? Regression aims to find coefficients that give the best possible fit. 169。 Procedure Partition (S) if ( purity (S ) ?p or |S| ?s ) then return。Silberschatz, Korth and Sudarshan Database System Concepts 6th Edition Classification Rules ? Classification rules help assign new objects to classes. ? ., given a new automobile insurance applicant, should he or she be classified as low risk, medium risk or high risk? ? Classification rules for above example could use a variety of data, such as educational level, salary, age, etc. ? ? person P, = masters and 75,000 ? = excellent ? ? person P, = bachelors and ( ? 25,000 and ? 75,000) ? = good ? Rules are not necessarily exact: there may be some misclassifications ? Classification rules can be shown pactly as a decision tree. 169。Silberschatz, Korth and Sudarshan Database System Concepts 6th Edition Data Warehousing ? Data sources often store only current data, not historical data ? Corporate decision making requires a unified view of all anizational data, including historical data ? A data warehouse is a repository (archive) of information gathered from multiple sources, stored under a unified schema, at a single site ? Greatly simplifies querying, permits study of historical trends ? Shifts decision support query load away from transaction processing systems 169。Silberschatz, Korth and Sudarshan Database System Concepts 6th Edition DecisionSupport Systems: Overview ? Data analysis tasks are simplified by specialized tools and SQL extensions ? Example tasks ? For each product category and each region, what were the total sales in the last quarter and how do they pare with the same quarter last year ? As above, for each product category and each customer category ? Statistical analysis packages (., : S++) can be interfaced with databases ? Statistical analysis is a large field, but not covered here ? Data mining seeks to discover knowledge automatically in the form of statistical rules and patterns from large databases. ? A data warehouse archives information gathered from multiple sources, and stores it under a unified schema, at a single site. ? Important for large businesses that generate data from multiple divisions, possibly at multiple sites ? Data may also be purchased externally 169。Silberschatz, Korth and Sudarshan Database System Concepts 6th Edition Data Mining (Cont.) ? Descriptive Patterns ? Associations ? Find books that are o
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