Disallowed variables

Disallowed variables are variables that cannot be used as query variables because the disclosure control rules forbid it. Any query made which contains one of these variables would always be blocked by the disclosure control rules.

Cantabular identifies disallowed variables at dataset build time so that it can identify them in APIs and thus user interface code can avoid offering them as choices to a user.

Disallowed variables can only be used with microdata-based datasets.

Cantabular identifies disallowed variables at dataset build time by performing a univariate query on each variable. Base variables are considered first and then variables derived from those variables. When an allowed variable is found then no variables derived from it are considered for evaluation as disallowed. Filter only variables are also not considered for evaluation as disallowed.

After this process is complete then Cantabular will check that all variables that are not disallowed and not filter only will pass a univariate query and will report an error if any fail.

Cantabular only evaluates the DRL querytest rules in order to determine whether a variable is disallowed or not. DRL rules should therefore be written such that these tests are performed in the querytest rules rather than in the tabletest rules. This is a good idea anyway because it means that queries are rejected before a table is constructed: computation which would be wasteful and cause an unnecessary delay in returning a response to the user.

APIs

In the Cantabular extended API the disallowed variables can be excluded or included using a disallowed argument on the variables field in dataset. Each variable also has a boolean isDisallowed field to indicate its status.

In the Cantabular server API the disallowed variables are supplied as disallowedVariables field on the dataset object. If there are any disallowed variables then this is populated with a JSON array of variable names.

Use case

The primary use case is for when low level rule variables are disallowed in particular datasets.