Steven P. Ketchpel

Software agents

The software world is one of great richness and diversity. Many thousands of software products are available to users today, providing a wide variety of information and services in a wide variety of domains. While most of these programs provide their users with significant value when used in isolation, there is increasing demand for programs that can interoperate – to exchange information and services with other programs and thereby solve problems that cannot be solved alone. Part of what makes interoperation difficult is heterogeneity. Programs are written by different people, at different times, in different languages; and, as a result, they often provide different interfaces. The difficulties created by heterogeneity are exacerbated by dynamics in the software environment. Programs are frequently rewritten; new programs are added; old programs removed. Agent-based software engineering was invented to facilitate the creation of software able to interoperate in such settings. In this approach to software development, application programs are written as software agents, i.e. software “components” that communicate with their peers by exchanging messages in an expressive agent communication language. Agents can be as simple as subroutines; but typically they are larger entities with some sort of persistent control (e.g. distinct control threads within a single address space, distinct processes on a single machine, or separate processes on different machines). The salient feature of the language used by agents is its expressiveness. It allows for the exchange of data and logical information, individual commands and scripts (i.e. programs). Using this language, agents can communicate complex information and goals, directly or indirectly “programming” each other in useful ways. Agent-based software engineering is often compared to object-oriented programming. Like an “object”, an agent provides a message-based interface independent of its internal data structures and algorithms. The primary difference between the two approaches lies in the language of the interface. In general object-oriented programming, the meaning of a message can vary from one object to another. In agent-based software engineering, agents use a common language with an agent-independent semantics. The concept of agent-based software engineering raises a number of important questions.

Coalition formation among autonomous agents

Coalitions of agents can work more effectively than individual agents in many multi-agent settings. Determining which coalitions should form (i.e., what agents should work together) is a difficult problem that is typically solved by some kind of centralised planner. As the number of agents grows, however, reliance on a central authority becomes increasingly impractical. This paper formalises the coalition formation problem in decision theoretic and game theoretic terms and presents a fully distributed algorithm that can efficiently determine coalitions that will be approximately “stable.” Stable coalitions are resistant to attempts of outsiders to break the coalition, because remaining in the coalition maximises the expected reward for each agent in the coalition. The algorithm is a variant of the “stable marriage matching with unacceptable partners” [6]. The Shapley value ([11], [12]) is suggested as a fair method to divide the coalitions utility among the members.

Making trust explicit in distributed commerce transactions

In a distributed environment where nodes are independently motivated, many transactions or commercial exchanges may be stymied due to a lack of trust between the participants. The addition of trusted intermediaries may facilitate some exchanges, but others are still problematic. We introduce a language for specifying these commercial exchange problems, and sequencing graphs, a formalism for determining whether a given exchange may occur We also present an algorithm for generating a feasible execution sequence of pairwise exchanges between parties (when it exists). Indemnities may be offered to facilitate previously infeasible transactions. We show when and how they enable commercial transactions.

Safeguarding and charging for information on the Internet

With the growing acceptance of the Internet as a new dissemination medium, several new and interesting challenges arise in building a digital commerce infrastructure. We discuss some of the issues that arise in building such an infrastructure. In particular, we study how one can find and pay for digital information, and how one can safeguard the information from invalid access and duplication. We use examples from our Stanford Digital Library Project to illustrate some of these problems and their potential solutions.

Shopping models: a flexible architecture for information commerce

In a digital library, there are many different interaction models between customers and information providers or merchants. Subscriptions, sessions, pay-per-view, shareware, and pre-paid vouchers are different models that each have different properties. A single merchant may use several of them. Yet if a merchant wants to support multiple models, there is a substantial amount of work to implement each one. In this paper, we formalize the shopping models which represent these different modes of consumer to merchant interaction. In addition to developing the overall architecture, we define the application program interfaces (API) to interact with the models. We show how a small number of primitives can be used to construct a wide range of shopping models that a digital library can support, and provide examples of the shopping models in operation, demonstrating their flexibility.

The Stanford InfoBus and Its Service Layers: Augmenting the Internet with High-Level Information Management Protocols

The Stanford InfoBus is a prototype infrastructure developed as part of the Stanford Digital Libraries Project to extend the current Internet protocols with a suite of higher-level information management protocols. This paper surveys the five service layers pro vided by the Stanford InfoBus: protocols for managing items and collections (DLIOP), metadata (SMA), search (STARTS), payment (UPAI), and rights and obligations (FIRM).

Competitive sourcing for Internet commerce

In electronic commerce on the Internet, a customer can choose among several competitive suppliers, but because of the nature of the Internet, the reliability and trustworthiness of suppliers may vary significantly. The customers goal is to maximize its utility, by minimizing the expense required to fulfil its request, and maximizing its probability of success by some deadline. To this end, the customer creates a request strategy, describing which suppliers to contact under what conditions. We describe models for representing request strategies complete with supplier reliabilities, delivery timeliness profiles, and customer deadlines. We also develop decision procedures for selecting request strategies that maximize expected utility under certain scenarios, and more efficient heuristics that approximate the optimal solution.

A sound and complete algorithm for distributed commerce transactions

Summary. In a multi-party transaction (also called a distributed commerce transaction) agents face risks from dealing with untrusted agents. These risks are compounded in the face of deadlines, e.g., an agent may fail to deliver purchased goods by the time the goods are needed. We characterize the risks, and present a distributed algorithm that mitigates these risks, by using pairwise exchanges and trusted intermediaries. The algorithm generates a safe sequence of actions that completes a commerce transaction without risk, if such a sequence exists. We show that the algorithm is sound (produces only safe multi-agent action sequences) and complete (finds a safe sequence whenever one exists). The initial restriction of guaranteeing safety even when none of the principals trusts another can be relaxed in some cases, so we show how to handle principals that do trust each other and interact directly rather than through a trusted intermediary.