The Historical Data Access (HDA) specification is primarily concerned with providing access to process control data that has been stored in a persistant data archive such as a SQL database.
HDA server may be a front-end for a proprietary historian or it could archive the data produced by one or more Data Access Servers. HDA servers are designed to facilitate analysis of trends over time and do not necessarily provide access to the data in real time.
HDA clients can read and write data stored in the HDA server. When reading HDA clients can request that the HDA server apply a statistical analysis on the data before returning it. |
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