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A Pen-based Database Interface for Mobile Computers

Rafael Alonso

V.S. Mani

Matsushita Information Technology Laboratory

2 Research Way, 3rd Floor

Princeton, NJ 08540



The appearance on the market of pen-based computers with wireless communication capabilities has led to the ability to access geographically distributed information bases. Moreover, such computing devices require database interfaces that are easy-to-use, avoid large scale data input via keyboard use, and are suited for smaller display screens. We establish the need for newer interfaces to deal with problems specific to mobile computing devices that use the pen as a primary input device. We describe an implementation of a pen-based graphical database interface on a pen computer (using the PenPoint operating system) with a built-in cellular phone. Using the cellular phone capability, the interface connects to remote databases and displays the schema information of the database chosen by the user. In response to gestures made by the user using the pen, the interface automatically generates queries and retrieves results. We use the Universal Relation concept to aid in automatically generating queries based on the attributes chosen by the user. We provide a summary of the status of this interface, some implementation details and suggest some future directions.

1 Introduction

The advent of pen-based computers with wireless communication capabilities (also known as Personal Communicators or Personal Digital Assistants) has opened the door to a new wave of possible applications. Users' expectations have grown beyond the obvious requirements of inter-personal communication (e.g. electronic mail), simple computations (e.g. spreadsheets), basic record-keeping (e.g. calendars), to more sophisticated requirements such as accessing information stored in geographically distributed information bases, including database management systems (DBMSs).

Typically, a DBMS is accessed either by directly supplying a data manipulation language such as SQL, or by accessing the data using an application program which embeds database commands. Most commercial DBMSs today support both interfaces.

As applications are ported to pen-based computers, users can continue to access DBMS information in the usual manner. However, the obvious approach of try-

ing to use character recognition software to translate pen strokes into SQL commands has several problems. First, the state of the art in handwriting recognition is such that writing more than a few words at a time is very cumbersome. Additionally, even if perfect character recognition were available, - and the state of the art as evidenced by the AT&T EOs ([EO93]) and the Apple MessagePads ([App93]) is far from perfect - a graphically-oriented interface is preferable for users than one based on direct SQL input. Furthermore, the size of the typical pen based computer is much smaller than that of a normal workstation, placing additional constraints on interface design. Indeed, the screen sizes of these devices vary from being as small as 15 square inches on the Apple MessagePads (Newtons") to about 48 square inches on the larger EO 880s. Finally, users are interested in accessing data having a complex schema, and thus require a more powerful interface than is possible by supporting solely SQL commands.

Thus, we believe that a powerful DBMS interface for mobile environments must have the following characteristics: (1) be graphically oriented (2) minimize pen-strokes (3) be more powerful than a simple SQL front-end and (4) make judicious use of the limited screen area. We have attempted to address these and other mobile interface issues as part of our work. Initially, we have tackled the first two issues just listed. Others, such as optimization techniques for smaller screen sizes, operations in the face of frequent disconnections, etc., will be addressed in the future.

Our basic approach is based on previous work in data modeling and in graphical user interfaces for databases. Our initial prototype has now been completed, and the status of the system is described here also.

2 The Interface

Most previous research on graphical user interfaces [AGS90, BH86, CERE90, KKS88, Kun92, SBMW91, Kim86] has made use of mouse operations to simplify user interactions. In pen-based environments, the mouse can almost always be replaced by the pen without any loss in functionality. However, workstation based GUIs typically use the keyboard to input large amounts of data. In a pen-based environment,