Secure databases
Quick reference
To create a secure Quanvert database or check the status of an existing database, type:
qvsecure [–x] [–i] [–m n] [–u] [–w]
Options
–x
Prints a message telling you how to run qvsecure.
–i
Gives information on the security status of the database.
–m n
Makes a database secure. n is the minimum unweighted value allowed in the database.
–u
Secure an unweighted database or the unweighted figures in a weighted database.
–w
Secure weighted figures.
More information
qvsecure enables you to make a Quanvert database secure, preventing access to weighted or unweighted information below a given value.
When you secure a Quanvert database using qvsecure, a hidden table of cells is produced for each table containing the raw counts of cases which belong in each cell (weighted for a weighted minimum; unweighted for an unweighted minimum). It is these values that are used to determine whether the values in a row or column should be suppressed.
Normally, only the first base row and first base column are inspected. If there is no base element in a direction, all values are inspected and the largest value is taken instead. When looking for this largest value, qvsecure only inspects data elements, such as those produced by n01 statements; qvsecure does not inspect elements which generate totals (summary elements), such as n04 and n12.
By default, Quantum calculates an
ex= element on an
n01 statement and uses the result and not the raw count when determining whether the values in a row or column should be suppressed. If you want to use the raw count, instead of the result of the calculation, use the
summary keyword on the
ex= element. For more information on using the
summary keyword, see
Treating data values as summary in secure databases.
Once a database has been made secure, options which are normally available in Quanvert are disallowed, as follows:
▪Creation of unweighted tables in weighted databases (wm=0 on individual elements within axes is ignored).
▪Creation of profiles and lists.
▪Export of the database to SAS, SPSS or ASCII.
To secure an unweighted database or to secure the unweighted values in a weighted database
Type:
qvsecure –m min_value –u
This causes unweighted absolute data with a value less than min_value to be replaced with the special characters defined with spechar= in the Quantum spec. For example:
qvsecure -m 100 -u
creates a secure database in which all unweighted absolute values less than 100 are replaced by special characters.
To make a weighted database secure for weighted values
Type:
qvsecure –m min_value –w
This causes weighted absolute data with a value less than min_value to be replaced with special characters.
You might secure a weighted database on weighted or unweighted figures but not on both. The –w option is disallowed when making an unweighted database secure. However, you must still specify –u since qvsecure has no default database type.
Provided that you enter a value for min_value that is greater than zero, and the first number in any row or column of the table is less than that value, then that number is replaced with the second spechar character and the rest of the row or column is replaced with the first spechar character. If you do not define any special characters for the database, Quanvert uses an asterisk as the second special character and a blank as the first.
If you define min_value as zero, do not use either –u or –w. Instead just use –m0 by itself. The database continues to indicate the other features of secure Quantum but no suppression of specific values occurs.
To change the security level of a database
Run qvsecure again with a different value for n.
To make a database ‘non-secure’
Reflip it.
To check the security status of a database
Type:
qvsecure –i
To check how to use qvsecure
Type:
qvsecure –x
See
See also