There has been considerable research in maintaining handwritten data within the database and using similarity-matching techniques to retrieve data. While some good results have been achieved already, there is clearly room for improvement. Even with improvements in the accuracy of similarity matching, there will always be some degree of error arising from the inherent variability in human handwriting. Thus, data retrievals over handwritten data must necessarily be approximate. Here again, the theme of managing uncertainly of data arises, though in a different setting than those discussed in earlier sections.
Similar issues exist for voice interfaces and spatial information.
This is a difficult and under-studied problem that deserves further research. The latter, when considered from the standpoint of millions and perhaps billions of users, is indeed a large-scale database problem representing a truly challenging focal point for future research. Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. Copyrights for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted.