For applications which lack a shared objective, economic theory provides a more useful perspective than CSCW. In a market economy, ``cost'' or ``price'' (the value discovered by a market) serves as a basis for allocating scarce resources. In the emerging information-based economy, both information itself and the tools which manage that information have economic value. This will result in the development of a market for not merely information and tools, but also for metainformation such as the annotations on which social filtering is based. The CSCW perspective will certainly be helpful when designing common standards for the exchange of price information and monetary instruments because all participants in a market benefit from such social structures. But when participants do not share common goals with respect to the use they make of the information they obtain, market dynamics provide a more effective way of allocating scarce information resources such as intellectual property and expert annotations.
The vast majority of experimental work on text filtering has exploited freely available information such as Internet News and messages sent to electronic mailing lists, so little reference to the cost of intellectual property can be found in that literature. On the other hand, users of commercial text filtering systems have developed profile construction techniques which which recognize differing costs for different aspects of access to intellectual property (e.g., selective purchase of limited redistribution rights) . Commercial text filtering systems typically require explicit profiles, however, and we are not aware of any research on implicit user models for text filtering which exploit cost information. Like the ratings we described in section 5.3.2, prices are a type of annotation, and hence they can be exploited by a social filtering system. The difference between prices and other annotations on which social filtering can be based is that there may be a firmer a priori basis for using cost information than for using other types of annotations, and that fact may prove useful when designing user models for text filtering.
In addition to these technical considerations, market formation also raises broad social issues. The creation of markets for information, for annotations, and even for the filtering systems themselves restricts information access to users for whom the value of the information justifies the cost of obtaining it. Such unrestrained market operation is rarely allowed, however. Governments and other social structures are often charged with regulation of economic activity in order to limit the effect of inequities that can result from market economics. The establishment of public libraries, the imposition of disclosure requirements for securities transactions, and the regulations which subsidize universal access to the telephone network with revenue generated from other sources provide instructive examples of how market forces can be adjusted to accomplish social goals. If information truly has value then such issues of equity will undoubtedly arise in information filtering as well.