Sometimes we may want to share a model with others but want to preserve the intellectual property that goes into building it. This happens, for example, when sharing your models with BayesFusion's Support. The Obfuscate... command can be used to create a new network from an existing network with an option to change various model properties while maintaining the original structure of the model.
The command invokes the following dialog
Output file allows the user to choose the location for the obfuscated network. Browse (
) button is convenient in finding room for the file on the local disk.
Obfuscation options
The check boxes on the left-hand side fulfill the following function:
❑ Open obfuscated file on completion leads to opening the obfuscated network in GeNIe.
❑ Change object names changes the names of objects in the model. These are typically names of nodes, submodels, and the network.
❑ Change object identifiers changes object identifiers in the model. These are typically identifiers of nodes, submodels, and the network. Because changing the identifiers may lead to communication problems with the recipient of the obfuscated network, Write map file option creates a file that maps the original with the scrambled identifiers.
❑ Change state identifiers changes the state names within discrete nodes in the model.
❑ Remove textboxes leads to removal of all text boxes that contains notes documenting the model.
❑ Remove annotations removes all annotations from the model (these are on arcs, nodes, node states, individual probabilities).
❑ Remove user properties removes all user properties defined for the model and its nodes.
❑ Change probabilities scrambles the numerical probabilities in the definitions of Chance nodes. See below for your choices of scrambling.
❑ Change utilities scrambles all numerical utilities in the definitions of Utility nodes. See below for your choices of scrambling.
❑ Remove diagnostic attributes removes any diagnostic properties defined in the model.
Definition scrambling
When at least one of the two options, Change probabilities or Change utilities, is checked, obfuscation involves scrambling the numerical parameters. There are three possibilities here:
Make uniform leads to replacing all probability distributions with uniform distribution
Roughen leads to rounding each of the parameters. Precision of the rounding is controlled by the (number of) Buckets parameter. When it's value is 10 (the default), all probabilities are rounded to the first digit after the decimal point.
Add noise leads to distorting all parameter with random noise. The process is controlled by the parameter Sigma, which is the standard deviation of the Normal distribution from which the noise is drawn. Adding noise is conducted by first transforming the parameter to odds, adding a random number from the Normal(0,sigma) distribution, and transforming the parameter back to probability. The entire distribution is re-normalized after this process to ensure that the sum of all probabilities is 1.0.
Prefixes
When a model is obfuscated, its elements will be assigned artificial names. You can control to some degree what these names will look like through specifying prefixes. Here are the default prefixes:
Node: n
Target node: t
Observ. node: o
State: s
Submodel: sub
Example
The following screen shots show the Hepar II network before (left) and after (right) obfuscation with the default settings.
Definitions of the node Chronic hepatitis before (left) and after (right) obfuscation with the default settings are shown below:
Please note that the default settings do not scramble the numerical parameters.
The obfuscation process creates two files on the disk: The obfuscated model (suffix .obfuscated.xdsl) and the mapping file (suffix .obfuscated.map). The latter is a text file containing a list of pairs of node IDs, the original and the obfuscated ID. When sharing the obfuscated model with somebody (e.g., with BayesFusion support folks), please do not send the map file, just the obfuscated model, as sending the mapping file along defies the purpose of obfuscation.