NISSWebSwap, Version 1.1

NISSWebSwap, Version 1.1

January, 2003

NISSWebSwap is a Web service that swaps one or more attributes (fields) between user-specified records in a microdata file, uploading the original data file from the user's computer and downloading the file containing the swapped records. The Web Services Description Language (WSDL) documentation for NISSWebSwap is included with the downloadable NISSWebSwap distribution, together with a NISS-developed client featuring a new graphical user interface (GUI) and demonstration files, or can be downloaded separately.

Data swapping is a strategy for protecting confidentiality in released microdata records. The purpose of data swapping is to introduce uncertainty into the mind of any user or intruder of the data as to whether records correspond to real data elements. Swapping does not change the marginal distribution of any attribute. Nor does it change either the joint distribution of the unswapped attributes or—if more than one attribute is swapped—the joint distribution of the swapped attributes. It does however, distort any joint distribution involving both swapped and unswapped attributes.

The principal functionality of NISSWebSwap is simultaneously to swap prescribed attributes in a specified fraction of the records in a database. The user specifies the data file containing the microdata records and the fraction of records for which the specified attributes will be swapped. NISSWebSwap provides additional capabilities to allow more refined implementation of data swapping, in the form of constraints on unswapped attributes, allowing the user to specify that two records will be swapped only if specified unswapped attributes are either equal (Example: Swapping may be allowed only for record pairs both drawn from the same state) or different (Example: records may be swapped only if they come from different counties).

The NISSWebSwap distribution contains: