DB Backward Compatibility Issue

[tchaithonov]

Hi Guys,

I used Eviews 7 to create and populate an edb, and when I tried to open it in Eviews 6, I have the following message:

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Database Error: file '...' has been corrupted (length inconsistent)

I have other edb's created by Eviews 7 but Eviews 6 can open them, so this message doesn't pop up for every single time. Would that be due to the length of variable names (shouldn't be, the maximum for Eviews 6 and 7 is the same) or some other things? Please let me know. Thanks.

Tchaithonov

[EViews Chris]

EViews 7 can create both version 6 and version 7 databases (which are not compatible with v6).

To create a version 6 compatible database, choose 'EViews v6 Database' from the Database/File Type drop down in the New Database dialog, or use 'type=eviews6' from the command line:

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dbcreate(type=eviews6) myev6db

You can tell what the format is from within EViews v7 by using 'View... Database Statistics'. A version 6 database will show up as 'version number: 2.0' a version 7 database will show up as 'version number: 4.0' (I'm afraid the numbering is a bit odd, but it is based on changes to the file format, rather than the EViews version number that supports the format).

Version 7 databases are incompatible because they support intraday frequencies, longer names (64 characters), and larger capacity (up to 64GB instead of 2GB). It's a shame that we couldn't make v6 give a better error message when it encountered a version 7 file, but the change in file capacity required us to change how we stored the file length, which is what is triggering the mysterious 'length inconsistent' message in version 6.

Note that EViews workfiles still have a limit of 24 character variable names, but you can use the longer variable names in databases to store multiple copies of workfile data (or data from a simulation, etc) in a database, without worrying about whether the names will become too long. For example, you could copy every object in a workfile to a database while adding a date suffix to every object:

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copy * myev7db::*_20100226

and then retrieve the objects saved on a particular day:

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copy myev7db::*_20100226 *

Even if the original workfile objects had names up to 24 characters long, date suffixes could still be appended to the names without causing the names to become too long for the database.