Communications and Data Interchange

successively refine the query if initially the query is not sufficient to locate information. In a wide area network, such a dialogue will become communication intensive. We are currently developing a prototype digita l library called DL-Raid at the Raid laboratory i n Purdue University. In this paper, we present ou r experimental studies about the effect of communications on the efficient retrieval of digital librar y data. We first discuss information retrieval schemes to increase retrieval effectiveness. Then , we study the implications of communications o n the efficiency and reliability of these retrieval schemes. We present and analyze results of communication experiments with large data objects. These experiments will help us categorize the retrieval methods based on how communication intensive they are. This characterization will include factors such as the number of messages interchanged , the size of query and the data retrieved , and the rate at which data is generated. For further information contact raidlab@cs. With the advent of powerful processing chips for real-time compression/decompression and emerging high-bandwidth communications networks , storing video data in a digital form seems to be a natural evolution. However, relatively little attention has been paid to the construction of such large-scale video storage systems. Based on a cost/capacity analysis, we found magnetic tap e storage represents the most economically viabl e choice for this purpose. Unfortunately, magneti c tape suffers from the problems of data longevity , large access time and small transfer bandwidth. In this paper, we address these issues by proposing a parallel tape striping approach to build cost-effective large-scale video storage servers. The problems associated with this approach are discussed i n detail and new techniques are developed to solv e them. Modern computer networks make it possible to distribute documents quickly and economically b y electronic means rather than by conventional pape r means. However, a major impediment to th e widespread adoption of services for electronic distribution of copyrighted material is the ease with which illicit copies can be made and disseminated. In this paper, we propose techniques that discourage illicit copying by embedding the document wit h unique codewords, These codewords can be inserted into the format file or bitmap image of a page. They are indiscernible by readers, howeve r they can be decoded from the image file to enable display or printing when matched to a sanctioned user's installation, or they can …