Service Brokering Yu-sik Park

Index Introduction Brokering system Ontology Services retrieval using ontology Example

Introduction In service-oriented distributed systems, software services are located in different computers The broker acts as middlemen between consumers and providers, aggregating, repackaging and adding value to services or information The brokering function in a distributed systems matches a request for a specific service with a remote process that can perform that service, based on subtask’s need for that service

The general broker model

Tasks of brokers Locational Task The broker should maintain an up-to-date repository of all of the agents available for access within an agent system. Matching Task The broker should maintain a knowledge base of advertised information about other agents, and uses this knowledge to match agents with requested services

Advertising Process An agent announces itself to broker by advertising to them, using the terms and vocabulary described in ontologies Broker that received the advertisement store all of the advertised information about agent in its repository

Querying Process The broker may receive queries from agents that are looking for other agent that can provide specific services. A query is represented as an individual capability specified over some set of focused ontologies.

Syntactic Brokering and Semantic Brokering Syntactic brokering uses the structure or format of a task specification to match a requester with a service provider, matching requests to object interfaces or query/scripting languages to decide which service providers to recommend Unfortunately, within an open agent-based system there may be situations where agents present the same interface, but implement different functions So, the agent system can add semantic functions to complement the syntactic brokering process

What is the Ontology? W3C defines the ontology in Requirements for a Web Ontology Language, “An ontology defines the terms used to describe and represent an area of knowledge”. Hence, a service ontology defines how a service is represented in the area of service discovery.

Why ontology? Sharing common understanding of the structure of information among people or software agents is one of the more common goal in developing ontologies Enabling reuse of domain knowledge was one of the driving forces behind recent surge in ontology research Making explicit domain assumptions underlying an implementation makes it possible to change these assumptions easily if our knowledge about the domain changes Separating the domain knowledge from the operational knowledge is another common use of ontologies

Focused Ontologies and Ontology Fragments When we consider how to represent the ontological knowledge, there are basically two approaches Incorporate everything into a single, very large ontology Allow for multiple, focused ontologies

Simple ontology example Class Attribute

Agent Capabilities, Advertisements and Queries Agent capabilities provides a mechanism for agents to advertise their abilities and characteristic to a broker agent, and to query the broker for sets of agents meeting specific criteria When more than one agent capability is advertised, semantic interpretation is similar to a disjunction

Example : Sembots The SemBots project is developing software technologies to realize self-growing robot software systems that enable robots to improve their high-level software configurations based on their experiences and user feedback in handing unknown situations. In project, we are developing Component broker Ontology based representation

Component broker of Sembots

References Marian Nodine, “Scalable Semantic Brokering over Dynamic Heterogeneous Data Sources in InfoSleuth”, MCC, April 20, 2001 A. Tokmakoff, “Service Brokering in Object-Based Systems: Advanced Information Services, IEEE

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