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Data migration is the process of transferring data between storage types, formats, or computer systems. It is a key consideration for any system implementation, upgrade, or consolidation. Data migration is usually performed programmatically to achieve an ''automated migration'', freeing up human resources from tedious tasks. Data migration occurs for a variety of reasons, including server or storage equipment replacements, maintenance or upgrades, application migration, website consolidation and data center relocation.〔Janssen C, Data migration, http://www.techopedia.com/definition/1180/data-migration (retrieved 12 August 2013)〕 To achieve an effective data migration procedure, data on the old system is mapped to the new system utilising a design for data extraction and data loading. The design relates old data formats to the new system's formats and requirements. Programmatic data migration may involve many phases but it minimally includes ''data extraction'' where data is read from the old system and ''data loading'' where data is written to the new system. After loading into the new system, results are subjected to data verification to determine whether data was accurately translated, is complete, and supports processes in the new system. During verification, there may be a need for a parallel run of both systems to identify areas of disparity and forestall erroneous data loss. Automated and manual data cleaning is commonly performed in migration to improve data quality, eliminate redundant or obsolete information, and match the requirements of the new system. Data migration phases (design, extraction, cleansing, load, verification) for applications of moderate to high complexity are commonly repeated several times before the new system is deployed. ==Categories== Data is stored on various media in files or databases, and is generated and consumed by software applications which in turn support business processes. The need to transfer and convert data can be driven by multiple business requirements and the approach taken to the migration depends on those requirements. Four major migration categories are proposed on this basis. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Data migration」の詳細全文を読む スポンサード リンク
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