The same type of tension between constrained and unconstrained system design occurs at many levels. Adopting an even broader perspective, it is apparent that users operate within a social system, and that system imposes social constraints on what is possible. Organizational aspects of networked communications are studied the field of Computer Supported Cooperative Work (CSCW), so text filtering is an issue for which the CSCW perspective can be informative.
Consider, for example, Denning's suggestion that users set up separate mailboxes for specific purposes and that senders direct electronic mail to the appropriate mailbox. In order to be effective, this approach would require that the user address messages correctly, that receivers organize their mailboxes in a useful manner, and that all of the software systems between the sender and the receiver support this addressing scheme. Standards development processes and competitive market mechanisms are two techniques for addressing such issues, and there are numerous examples of the practicality of such schemes (e.g., Lotus Notes and Internet News). Because many of the constraints on such efforts are social rather than technical, the breadth offered by the CSCW perspective is essential to the success of such endeavors.
Once such social conventions are created to add the necessary structure to the documents, text filtering techniques provide a way to exploit that information. For example, the current interest in assigning ``ratings'' to World Wide Web pages to facilitate parental control of the information available to their children presumes the availability of technology to exploit that information. The design a system for creating, distributing, and using these ratings is an issue best studied from the perspective of CSCW because a common task motivates multiple participants. Ratings are, however, simply one type of annotation. So an understanding of how annotations are used in information filtering systems can provide useful insight into how those annotations could be integrated with other sources of information about the contents of a document.