DW Lecture IV (2)

DW Lecture IV (2) - Datawarehousing and...

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By Dr. Atanu Rakshit Data warehousing   and  Business Intelligence using SAS (Lecture VI)
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2 Course Overview The course: what and how 0. Introduction: The Past and The  Problem I. Data Warehousing II. Decision Support and OLAP III. Data Mining IV. Usage of SAS for DW and DM V.  Business Intelligence and its use VI. Looking Ahead
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3 Introduction The Past and The Problem
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Chapter 12:  Indexing and Hashing Basic Concepts Ordered Indices  B+-Tree Index Files B-Tree Index Files Static Hashing Dynamic Hashing  Comparison of Ordered Indexing and Hashing  Index Definition in SQL Multiple-Key Access
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Basic Concepts Indexing mechanisms used to speed up access to desired  data. E.g., author catalog in library Search Key  - attribute to set of attributes used to look up  records in a file. An  index file   consists of records (called  index entries ) of the  form Index files are typically much smaller than the original file  Two basic kinds of indices: Ordered indices:   search keys are stored in sorted order Hash indices:   search keys are distributed uniformly across  “buckets” using a “hash function”.  search-key pointer
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Index Evaluation Metrics Access types supported efficiently.  E.g.,  Records  with a specified value in the attribute Or records with an attribute value falling in a specified range of  values. Access time The time it takes to find a particular data item Insertion time The time it takes to insert a new data item Deletion time The time it takes to delete a data item Space overhead The additional space occupied by an index structure
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Ordered Indices In an  ordered index index entries are stored sorted on the  search key value.  E.g., author catalog in library. Primary index in a sequentially ordered file, the index whose  search key specifies the sequential order of the file. Also called  clustering index The search key of a primary index is usually but not  necessarily the primary key. Secondary index :   an index whose search key specifies an  order different from the sequential order of the file.  Also called  non-clustering index . Index-sequential file :  ordered sequential file with a primary  index. Indexing techniques evaluated on basis of:
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Dense Index Files Dense index  — Index record appears for  every   search-key value in the file. 
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Sparse Index Files Sparse Index :  contains index records for only some search-key  values.
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DW Lecture IV (2) - Datawarehousing and...

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