Problems arise because these tools are too often expected to provide broader coverage than their designs permit. The limitations of prevention tools are that (1) there is typically a large gap in time between the identification of the vulnerability and the availability of the solution, and (2) partial and faulty deployment resulting in gaps in coverage. Tools for response to individual attacks typically have significant false negative rates (e.g., tunneling through firewalls) or high false positive rates (intrusion detection systems). With these tools, there is also a gap between the onset of new types of attack and when signatures/rules become available to handle them.

The Open Agent Architecture (OAA), developed and used for several years at SRI International, makes it possible for software services to be provided through the cooperative efforts of distributed collections of autonomous agents. Communication and cooperation between agents are brokered by one or more facilitators, which are responsible for matching requests,from users and agents, with descriptions of the capabilities of other agents. Thus it is not generally required that a user or agent know the identities, locations, or number of other agents involved in satisfying a request. OAA is structured so as to minimize the effort involved in creating new agents and "wrapping" legacy applications, written in various languages and operating on various platforms; to encourage the reuse of existing agents; and to allow for dynamism and flexibility in the makeup of agent communities. Distinguishing features of OAA as compared with related work include extreme flexibility in using facilitator-based delegation of complex goals, triggers, and data management requests; agent-bused provision of multimodal user interfaces; and built-in support for including the user as a privileged member of the agent community.This article explains the structure and elements of agent-based systems constructed using OAA. The characteristics and use of each major component of OAA infrastructure are described, including the agent library, the Interagent Communication Language, capabilities declarations, service requests,facilitation, management of data repositories, and autonomous monitoring using triggers. To provide technical context, we describe the motivations for OAA's design, and situate its features within the realm of alternative software paradigms. A summary is given of OAA-based systems built to date, and brief descriptions are given of several of these.

The design and development of the Open Agent Architecture (OAA)3 system has focused on providing access to agent-based applications through an intelligent, cooperative, distributed, and multimodal agent-based user interface. Only the primary user interface agents need run on the local computer, thereby simplifying the task of using a range of applications from a variety of platforms, especially low-powered computers. An important consideration in the design of the OAA was to facilitate the reuse of agents in new and unanticipated applications, and to support rapid prototyping. The utility of the agents and tools developed has been demonstrated by their use as infrastructure in unrelated projects.

During the past year, signiicant improvements have been made in the natural-language processing technology used in the SRI ATIS spoken-language understanding system. The principal developments have been (1) the incorporation of information from the natural-language grammar and lexicon into a statistical language model that is used in both recognition and understanding, (2) implementation of a robust interpretation component that constructs queries out of grammatical fragments when an utterance cannot be analyzed as a single phrase or utterance, and (3) a new context mechanism for air travel planning that constructs an explicit model of the user's intended itinerary.

SRI International participated in the June 1990 Air Travel Information System (ATIS) natural-language evaluation. This report briefly describes the system that SRI used in the evaluation, analyzes SRI's results, and makes some recommendations for changes in the database structure and data collection system to be used for future ATIS evaluations.

This paper shows how the integration of natural language with direct manipulation produces a multimodal interface that overcomes limitations of these techniques when used separately. Natural language helps direct manipulation in being able to specify objects and actions by description, while direct manipulation enables users to learn which objects and actions are available in the system. Furthermore, graphical rendering and manipulation of context provides a partial solution to difficult problems of natural language anaphora.

An algorithm for generating the possible quantifier scopings for a sentence, in order of preference, is outlined. The scoping assigned to a quantifier is determined by its interactions with other quantifiers, modals, negation, and certain syntactic-constituent boundaries. When a potential scoping is logically equivalent to another, the less preferred one is discarded.The relative scoping preferences of the individual quantifiers are not embedded in the algorithm, but are specified by a set of rules. Many of the rules presented here have appeared in the linguistics literature and have been used in various natural language processing systems. However, the co-ordination of these rules and the resulting coverage represents a significant contribution. Because experimental data on human quantifier-scoping preferences are still fragmentary, we chose to design a system in which the set of preference rules could be easily modified and expanded.The algorithm described has been implemented in Prolog as part of a larger natural language processing system. Extensions of this algorithm are in progress.

We present an object-oriented architecture for a computer-based, real-time, multimedia conferencing system. This architecture divides the system into five functional areas: a multimedia shared workspace, a user interface, conference management, communications, and an information base. The structure and operation of the first four areas are modeled with object-based concepts that address design requirements identified during the development of a proof-of-concept prototype, that preceded the architecture specification. The shared workspace, the most important component, is thoroughly discussed; the other components support its realization. The modeling of workspace entities emphasizes their aggregation into composed entities and the homogeneous handling of several data media. The user interface manages uniformly the man-machine interaction for both local and remote user actions. Conference management deals with session establishment, participation, and control of multiple media floors. The communication functions replicate user actions over workspace objects in all hosts participating in a conference, matching traffic types with transmission services in the process.

The design and development of the Open Agent Architecture (OAA)l system has focused on providing access to agent- based applications through an intelligent, cooperative, dis- tributed, and multimodal agent-based user interfaces. The current multimodal interface supports a mix of spoken lan- guage, handwriting and gesture, and is adaptable to the user's preferences, resources and environment. Only the primary user interface agents need run on the local computer, thereby simplifying the task of using a range of applications from a variety of platforms, especiall y low-powered computers such as Personal Digital Assistants (PDAs). An important consid- eration in the design of the OAA was to facilitate mix-and- match: to facilitate the reuse of agents in new and unantici- pated applications, and to support rapid prototyping by facil- itating the replacement of agents by better versions. The utility of the agents and tools developed as part of this ongoing research project has been demonstrated by their use as infrastructure in unrelated projects.