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Frequently asked questions (FAQ): General

• What is OPCHDB?
• Which operating systems are supported?
• Can the OPC DA Client or OPC HDA Server run as services?
• Is there a Linux version? Or a version for Windows CE?
• Can I send suggestions for new functionality?
• Can we create a link to www.realtimeexecutives.com?
• Can I store time stamped values in the database?
• Can I change the values stored in the database?
• Why are flat files used for the database data files?
• What happens if I run "Virus Scan" programs with the OPCHDB?
• Back to main support area
  

Q: What is OPCHDB?
A: OPCHDB is a standard OPC based historian comprised of the following five components, OPC DA Client, Historical Database, OPC HDA Server, Quick Report and Quick Graph.

• The OPC DA Client interface allows data to be input to the Historical Database from OPC DA Servers.
• The Historical Database is an extremely efficient database using the 'flat file' model in which historical values are stored time-sequentially.
• The OPC HDA Server interface provides stored historical data to OPC HDA Clients using the OPC HDA (Historical Data Access) 1.0 specification.
• The Quick Report allows for a simple way of reporting historical data from the Historical Database.
• The Quick Graph allows for a simple way of viewing historical data from the Historical Database.

Q: Which operating systems are supported?
A: OPCHDB uses 32 bit applications. These require Windows NT 4.0, Windows 2000, or Windows XP.

Q: Can the OPC DA Client or OPC HDA Server run as services?
A: Unfortunately, not at this time, however it is on our development list for a future release.

Q: Is there a Linux version? Or a version for Windows CE?
A: Unfortunately not.

Q: Can I send suggestions for new functionality?
A: Yes, please! If possible, send your suggestions clearly separated and numbered, and as short as possible. Unfortunately our wish list is already very long, so we cannot guarantee if or when your wish will be implemented.

Q: Can we create a link to www.realtimeexecutives.com?
A: We would be very pleased as long as your pages do not contain illegal content or offensive material. However, in most cases we cannot offer a link back to your site.

Q: Can I store time stamped values in the database?
A: No. The database only supports periodic data collected at a fixed rate. A value is stored into the database at every interval.

Q: Can I change the values stored in the database?
A: No. The database is READ-ONLY by design. This is for security reasons.

Q: Why are flat files used for the database data files?
A: The database architecture, using flat files stored in a directory tree, provides for an extremely efficient database in which historical values are stored time-sequentially in 4-byte floating-point format. The number of files in each directory is calculated to minimize the time to find any single file. Once a file is located, the timestamp is used as an index into the flat file. This allows for very fast data retrieval since a single read can return one (1) value or hundred (100) values in about the same time. Also, the data files are cyclical so that once they are filled up, the oldest data is written over with new data. This reduces the database administration.

Q: What happens if I run "Virus Scan" programs with the OPCHDB?
A: Most "Virus Scan" programs normally scan any file that is changed. OPCHDB updates, that is, changes data store files on a regular basis. When this occurs the "Virus Scan" program can use up an inordinate amount of CPU processing  time checking the updated files. If this becomes a problem, consider disabling the "Virus Scan" program on the computer where the OPCHDB is running.