Csci12 report aug18
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Transcript of Csci12 report aug18
Index
• Indexes provide fast searching of a table based on one or more key columns. Indexes on foreign keys can also
greatly improve the performance of join.
• Records in indexed sequential files are stored in the order that they are written to the disk.
• Records may be retrieved in sequential order or in random order using a numeric index to represent the record number in file
Properties
• Primary Storage Area: Records in indexed sequential files are
stored in the order that they are written to the disk. Records may be retrieved in sequential order or in random order using a numeric index to represent the record number in the file.
Properties
Records are stored sequentially, originally to speed access on a tapesystem. In contrast, a relational databaseuses a query optimizer which automaticallySelects indexes. The record size, specifiedwhen the file is created, may range from 1 to8000 bytes.
Properties
2. Separate Indexes:The Indexed Access method of reading or writing data only provides the desiredoutcome if in fact the file is organized as anISAM file with the appropriate, previouslydefined keys. Access to data via thepreviously defined key(s) is extremely fast.
Properties
Multiple keys, overlapping keys and key compression within the hash tables are supported. A utility todefine/redefine keys in existing files isprovided. Records can be deleted, although"garbage collection" is done via a separateutility.
Properties
3. Overflow Area:When an ISAM file is created, index nodes are fixed, and their pointers do notchange during inserts and deletes that occurlater (only content of leaf nodes changeafterwards).
Properties
node exceed the node's capacity, new records are stored in overflow chains. Ifthere are more inserts than deletionsfrom a table, these overflow chains cangradually become very large, and thisaffects the time required for retrieval of arecord.
Properties
Indexed sequential files: commonly used for transaction files because they take less disk space thankeyed files, and are faster to read frombeginning to end than a keyed file.
Data Warehousing
What is a Data Warehouse?
DW is a subject-oriented, integrated, time-variant, and nonvolatile collection of data intended to
support management decision making
Data Warehousing
What is a Data Warehouse?
DW is a subject-oriented, integrated, time-variant, and nonvolatile collection of data intended to support management decision making
Data Warehousing
DATABASE vs DATA WAREHOUSE
Database: transactional (relational, object-oriented, network, heierarchical)
Data Warehouse: mainly INTENDED for decision support applications
**optimized for retrieval not routine transactional processing**
Data Warehousing
What is a Data Warehousing?
combining multiple and usually varied sources into one comprehensive and easily manipulated database. (wiseGEEK.com)
Data Warehousing
Properties:
1. Organized around major subject areas of an org. (i.e. sales ,suppliers,products, etc.)
2. Integrated from multiple operational OLTP data sources ** OLTP = OnLine Transaction Processing db
Data WarehousingProperties:
3. Periodic updates (based on schedules)
There is a trend wherein updates are gearing towards near real-time reporting of business analytics.
Data Warehousing
Advantages:2.Competitive advantage3.Increased productivity of corporate decision makers3. Potential high return on investment as the
org. Finds the best way to impove efficiency and/or profitability
Data Warehousing
Encountered Problems:2.Underestimation of resources required to load the data2. Hidden data integrity problems in source data3. Omitting data later found to be required
Data WarehousingEncountered Problems:
4. Ever increasing end user demands5. Consolidating data from diparate data sources 6. High resource demands (huge amount of
storage; queries that process millions of rows)
7. Ownership of data