Agents and the Semantic Web• Knowledge-based (Expert) System research reached

several interesting conclusions– While extremely useful, such systems are enormous

undertakings (dozens to hundreds of man-years per system)– With proper tools (shells, languages), non-AI people can

construct these systems– Automated knowledge acquisition reduces the effort needed to

construct them– They are brittle because they lack general knowledge

• KBS construction moved out of the active realm of AI research, but it was realized that we still need systems that can reason autonomously and apply worldly knowledge– This becomes even more critical as we focus on how we might

use the distributed knowledge available on the WWW– This led to research into more primitive forms of reasoners:

the intelligent agent

Agents: Some Definitions• There is no single definition that adequately covers

what everyone wants an agent to be but there are several commonly cited features:– Autonomous – must be able to work on its own to solve

the problem– Communicative – must be able to communicate with other

agents or knowledge sources to acquire knowledge or data– Goal-oriented – must be able to, given a task, figure out

how to solve the task and work toward that go– Perceptive – must be able to sense its “environment”– Mobility – must be able to move within its environment *– Sociability – ability to communicate with a human during

problem solving *• To define an agent, which features are necessary?

– * these features are not required by all researchers• Will these features help us identify what an agent is?

What Does Autonomy Require?• First and foremost, the agent must know how to

solve the given problem– It must have its own

• problem solving method(s)

• knowledge-base

• ability to acquire necessary input

– Fortunately, unlike KBS, the methods and knowledge-base content are limited to a very specific problem, so constructing the agent should be more straightforward

– How does the agent know where to seek the necessary input?

• do we want to provide a static list of sources?

• can the agent find proper sources in a dynamic environment?

Communication• Agents need to be able to communicate with other

agents– An agent must know what other agents exist and how to

contact them• a static list may not be useful, consider how dynamic the web is

– An agent must be able to send messages that other agent(s) can understand

– An agent must be able to understand or interpret responses from agents

• ontologies can be used to help facilitate the actual exchange of information since it is unlikely that the two agents will “speak the same language”

– An agent must know which of the available agents can accommodate the request of this agent

• for instance, which agent can answer question X or supply datum Y?

– An agent may want to know what other agents are trustworthy (can I trust the response from that agent?)

Types of Environments• Accessible vs. inaccessible: agent’s sensors give it access to

the complete state of the environment at each point in time• Deterministic vs. non-deterministic: next state of the

environment is completely determined by the current state and the action executed by the agent

• Single agent: the agent works in isolation (no other agents around)

• Episodic vs. non-episodic: agent’s experience is divided into atomic episodes, each episode consisting of a perception-action pair where the action is a single action/event

• Static vs. dynamic: environment is unchanged during the agent’s deliberation of an action

• Discrete vs. continuous: limited number of distinct, clearly defined percepts and actions

Example Environments• The easiest environment to understand is that of a robot

– the robot can use a variety of sensors: visual (camera), radar/sonar, audio, heat, tactile, etc

– a robot might need to sense if• something is in the way• an object has been given to it and if that object is the object expected• the terrain is level

• On other hand, an environment may be artificial– a softbot in a flight simulator will receive input from the flight

simulator but the input is as information-rich as a physical environment

• An agent situated in a network also senses an artificial environment but the environment here is limited– communication passing across the network intended for

different agents or network nodes– the agent only has to distinguish if a message is meant for it

and then interpret the message

Examples

An environment would be considered semi-static if the environment is not changing between agent decisions but if the agent is on a time limit – for instance, in timed chess, the agent has to watch the clock or else be penalized (or lose) if time runs out

The Problem of Mobility• True mobility means some degrees of freedom

– This may be physical motion like a robot that has a robotic arm, or an autonomous vehicle

– Or it may be a process that is able to move from one processor to another – it’s freedom is in that it can choose to migrate elsewhere

• If we restrict “mobile” to the above two forms of degrees of freedom, then we disallow most forms of software as not being agents, or we have to remove this attribute from the list of what agents should do– Communication is not mobility and most software on the

Internet (or other networks) do not move from processor to processor but instead send out messages/requests

• Is the distinction important?– If a process cannot migrate but can communicate, why

should we care?

What is and What is Not an Agent?• We have to be careful in defining an agent

– All too often, the definition is so loosely based that it can include any software product

– For instance, any computer program can be thought to be the following

• autonomous – program works on its own to solve the problem• communicative –program communicates with other programs• perceptive – program receives input from various sources• goal-oriented – program has an implicit function (goal)

• So how do intelligent agents differ?– For one, we hope that an intelligent agent can plan and handle

surprising circumstances– For another, the environment might be more than merely user

input

Examples: Are They All Agents?

An Agent Classification

• Some comments– Viruses have goals and mobility, but are they

communicative or perceptive?– Artificial life forms may not qualify as their only goal

is to survive and they may not be perceptive

How Does an Agent Differ from AI?• Many AI systems have been developed that are autonomous,

goal-oriented (in that they plan actions) and perceive their environment

• Why create a distinction between ordinary AI and agents?– the KBS sits in isolation, communicating with a user to solve its

problem– an agent communicates with other agents and interprets what those

agents communicate to them– the agent will reason (plan out) how to solve the problem by using

its own mechanisms as well as drawing upon other agents• On the other hand

– an agent will not typically require the depth of knowledge that a KBS will

– an agent may not need to utilize uncertainty handling– an agent may require worldly knowledge, common sense

knowledge, or natural language capabilities that the KBS does not require

• Generally, an agent should be easier to implement than a KBS

Agent Architecture• The agent operates as follows given a goal to accomplish

– sense the environment– plan out a course of actions– select the next action to perform which will modify the

environment and state– repeat until Goal has been reached

Env

iron

men

t

How difficult is it tosense the environment?

Will actions necessarilyaccomplish the plan stepas expected?

Can other agents influence the environment?

How are the plans storedand selected?

Types of Agents• Reflex Agent

– simplest form, the agent merely reacts to its environment – no memory, no internal states, no planning

• State-based Agent– the next step up is an agent that keeps track of its current (and

possibly previous) state(s), this can help with planning and understanding

• Goal-oriented Agent– this agent has the ability to plan out a sequence of states to

achieve in order – planning might be based on a table-lookup approach or something more elaborate using a search mechanism and available planning knowledge

• Utility-based Agent– the agent has the ability to determine the usefulness of a plan

step toward achieving its goals so that it can achieve the goals in a more optimal fashion, and possibly have better final results for goals

Comparison

Representative Agents• An agent which represents your interests

– This implies that the agent has some knowledge or understanding of your desires, goals, interests

– Examples:• email filter agent – not only to filter out spam, but to prioritize

messages• shop-bot agent – knows your preferences on the items being

shopped, and knows your monetary restrictions• FAX – an email responding agent (or even a phone answering

agent) that will mimic your responses to anticipated inquiries– Representative agents may require

• the ability to communicate in natural language• the ability to explain itself to the person being represented• some common sense reasoning capability • the ability to judge what is trivial and therefore does not require

your attention– Planning capabilities may not necessarily be needed

Learning (Adaptive) Agents• Reactive learning – based on previous failed attempts• Caching solutions – case based reasoning or chunking• Novel learning – learning new ideas as they are faced

– this might including learning new plan steps, learning new agents to communicate with, learning that previous plan steps can accomplish goals

• A learning component requires a solution to the utility problem– How do you know that the new piece of knowledge is worth saving? – How do you index this new piece of knowledge?– Do you discard older

knowledge in favor of the new? • While we prefer adaptive

agents, learning is a very challenging problem which may interfere with the performance of the agent

RETSINA Agents• RETSINA: Reusable Environment for Task-

Structured Intelligent Networked Agents – See http://www.cs.cmu.edu/~softagents/intro.htm– The idea is that communication between agents is

problematic• how does an agent know who to communicate with in a dynamic

environment and can they communicate correctly?

• RETSINA uses matchmaker (or middleware) agents to facilitate communication between agents– The environment being operated on is open and dynamic

so that agents may be added or deleted from the environment, and agent capabilities might change over time

– Additionally, the network environment is uncertain – an agent may or may not be available when next needed

– Agents may fail (that is, an agent is not assumed to always be correct)

RETSINA Agent Properties• Types of agents:

– Interface agents interact with users, receive user input, and display results

– Task agents help users perform tasks, formulate problem-solving plans and carry out these plans by coordinating and exchanging information with other software agents

– Information agents provide intelligent access to a heterogeneous collection of information sources

– Middle agents help match agents that request services with agents that provide services

• Communication and Coordination module accepts and interprets messages and requests from other agents

• Planning module takes as input a set of goals and produces a plan that satisfies the goals

• Scheduling module uses the task structure created by the planning module to order the tasks

• Execution module monitors this process and ensures that actions are carried out in accordance with computational and other constraints

RETSINA Agent Architecture

The Semantic Web• We now define an improved WWW, the Semantic Web

– The WWW is currently a syntactic structure• you find information through syntactic URLs

• and you search using search engines that primarily do keyword (syntactic) matching

– To fully utilize the knowledge of the WWW, we need to add semantics

• now we have a problem, in providing semantics to a piece of knowledge, how do I know that my interpretation will match yours?

• this is where an ontology can come in

– The idea behind the Semantic Web is to• modify the WWW to include semantic information for every available

resource

• the semantic information might be supplied by human, or annotated automatically through some software process (where possible)

• add intelligent agents to harvest the knowledge from the web

Detailed Example• From the Berners-Lee/Hendler/Lassila article• Mom needs to see a specialist and then has to have a

series of physical therapy sessions (biweekly)• We want our intelligent agent set up the appointments

– Lucy will drop off mom and Pete will pick her up– Lucy’s agent knows mom’s prescribed treatment (from the

doctor’s agent) • Lucy’s agent

– looks up several lists of providers– checks for the ones in-plan for Mom’s insurance within a 20-

mile radius of her (Mom’s) home and with a rating of excellent or very good on trusted rating services

– begins to find a match between available appointment times (supplied by the agents of individual providers through their Web sites) and Lucy’s schedule

Continued• The initial schedule is compared with Pete’s agent which

detects a conflict: the selected hospital is across town and the pick up time is during rush hour

• Pete’s agent queries:– “Can we either change the appointment time or the

appointment location?”

• Lucy’s agent trusts Pete’s agent • Pete’s agent finds a new location/time but finds

– that Pete would have to reschedule a couple of his less important appointments

– the hospital selected is not included on the insurance company’s list of providers under physical therapists

– however, Pete’s agent can confirm that this hospital will be covered on the insurance company citing a different source

Example Concluded• Pete must get involved at this point

– he confirms that the less important appointments can be rescheduled but trusts that the agent found accurate insurance information

• Pete confirms the new plan to his agent and since Lucy’s agent trusts Pete’s agent, Lucy’s agent confirms as well on behalf of Lucy

• Here are some comments on the example:– Autonomous actions

• each agent was able to come up with a plan given the initial goal of “make appointment” with the given constraints

– Communication• the two agents communicated to each other and presumably

to other agents (hospital agents, insurance company agents, doctor’s agents)

Comments Continued• Sociability

– When necessary, Pete’s agent communicated to Pete the problems (appointments needing to be rescheduled, insurance question)

– But in the case of the insurance problem, the agent was able to offer a separate source for information

• Use of Ontologies– Although not stated, it is likely that the agents would have to

appeal to various ontologies to perform their planning– For instance, Pete’s agent was able to determine that the

doctor/hospital was covered under the mother’s insurance policy, not through the insurance web portal, but through some other means

• Notice that neither agent was mobile – the problem did not call for this

More on the Semantic Web• There are other issues to consider including trying to

determine the reliability of another agent– If one representative agent communicates with another

representative agent, we have a situation where the representative agents are both trying to communicate in favor of the person they are representing

– In negotiations, this means that both representatives will try to achieve the goals of the individual they represent though any justifiable means

• being intentionally or unintentionally misleading• not divulging all relevant information (unless asked)• cheating

– There is a whole new problem being studied of determining whether an agent can be trusted

– This is as much a matter of psychology as it is computer science as we now must include mental models in our agent’s environment

• the mental model of the other agent or human that the agent represents

Multi-Agent Systems• We also need to differentiate between

– an agent that has subroutines to accomplish its task– and multiple agents that work together to accomplish a task

• In the latter case– how does one agent know what other agents to communicate

with?– how do the agents communicate (message passing? remote

procedure calls?)– what happens if a communication is interrupted?– will there be multiple agents that could accomplish a given

task so that one agent can call upon several agents and then select among the responses?

– will there be a single governing agent?• These problems are similar to any distributed process but

now it becomes more convoluted as we step up from simple processes to goal oriented processes

How the SW Works: The URI• The uniform resource identifier

– Somewhat like a URL used in an http statement, this is the Internet address of a resource (document, web page, image file, executable, etc)

– The URI may utilize html, xml or xslt

• The syntax is schemetype : address and can optionally be followed by a query and/or a fragment that contains a direction for a secondary source– The scheme type will include http, ftp, mailto, src, tel, file

– The address which is scheme dependentfoo://usr1:pswd@locale.com:8042/pub/stuff/file.dtb;type=animal?name=ferret#nose \ / \________________/\_____/ \__/\_______/ \_____________/ \__________/ scheme userinfo hostname port path filename query fragment

How the SW Works: RDF• The resource description framework is a language

for representing information about resources on the web– The RDF will include a URI but also metadata that will

help an agent identify if this is the right resource or how useful the resource might be

• author of the resource, copyright info, licensing info, price, availability or consumer information, etc

• the metadata is not intended for human eyes– RDF is written in XML (or XML-like notation)

<?xml version="1.0"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:contact="http://www.w3.org/2000/10/swap/pim/contact#"> <contact:Person rdf:about="http://www.w3.org/People/EM/contact#me">

<contact:fullName>Eric Miller</contact:fullName> <contact:mailbox rdf:resource="mailto:em@w3.org"/> <contact:personalTitle>Dr.</contact:personalTitle>

</contact:Person> </rdf:RDF>

More on RDF• An RDF expression is a collection of triples where each

triple is a subject, an object and a predicate (or property) – The subject or object can be a URI, a literal value, or a blank

(basically a distinct object that is not referenced by any other RDF expression)

• blanks (known as blank nodes) can be used as a collection of pointers to other URIs

– Literal values can be names, dates, numbers, etc and while literal value could be stored in a URI, the ability to use literals makes an RDF expression more concise, literals can also contain XML tags

RDF Example<rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"> <ex:editor>

<rdf:Description> <ex:homePage>

<rdf:Description rdf:about="http://purl.org/net/dajobe/"> </rdf:Description>

</ex:homePage> </rdf:Description> </ex:editor> </rdf:Description> <rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"> <ex:editor> <rdf:Description>

<ex:fullName>Dave Beckett</ex:fullName> </rdf:Description> </ex:editor> </rdf:Description><rdf:Description rdf:about="http://www.w3.org/TR/rdf-syntax-grammar"> <dc:title>RDF/XML Syntax Specification (Revised)</dc:title> </rdf:Description>

How the SW Works: Ontologies• Now that we have revamped the WWW to

include the metadata that can be used by Internet agents, we can populate the web with knowledge sources– We use ontologies to describe the knowledge

• DAML (DARPA Agent Markup Language) was a first attempt at an ontology language, DAML+OIL added the Ontology Inference Layer, and now DAML+OIL has become OWL, the primarily used ontology language

– How do we use the ontology?• the next slide represents the class wine, and we can use

the knowledge to infer, for instance, that wine is a physical thing, it is a drink, it is made from grape

OWL Entry<owl:Class rdf:ID="Wine"> <rdfs:subClassOfrdf:resource="&food;PotableLiquid"/>

<rdfs:subClassOf> <owl:Restriction>

<owl:onPropertyrdf:resource="#madeFromGrape"/><owl:minCardinalityrdf:datatype="&xsd;NonNegativeInteger"> 1</owl:minCardinality> </owl:Restriction>

</rdfs:subClassOf> <rdfs:subClassOf> <owl:Restriction>

<owl:onPropertyrdf:resource="#locatedIn"/><owl:minCardinalityrdf:datatype="&xsd;NonNegativeInteger"> 1</owl:minCardinality>

</owl:Restriction> </rdfs:subClassOf></owl:Class>

How the SW Works: Inferences• Much of the knowledge in an ontology is class-

subclass and class-property• How do we make inferences?

– Inheritance: anything true of a class is true of a subclass

• what about multiple inheritance?

– Property inference: if a class has a property and we know X is true about a property, then we infer X is true of the class (see the next slide for some types of properties)

– Subset relationships similarly allow property inference from the set where we can apply transitivity

– Instances: anything true of a class is true of an instance of the class

Example Ontology Properties• Aside from subtype of, when given a list attributes

or properties, we can use– intersection of, union of, complement of, one of

• Cardinality – default value or range, is a property universal, existential, or qualified?

• Made from – manufactured vs. natural, restrictions on which entries are made from this thing

• Equivalent class• Datatype property – specialized property for given

data type, can include data range and domain• Spatial property(ies) – contained in, adjacent to, on

top of, etc• Temporal property(ies) – co-occuring, preceding,

overlapping, following, one-time

How the SW Works: Agents• Finally, we have our Internet agents as described

earlier in these notes– When given a task, the agent has a plan to accomplish

the task• the plan may be static or adaptive

– The plan will usually draw upon knowledge sources and other agents

• seek information from ontologies, possibly translating terms as needed

• use inferences on ontology information• find other sources if a given source is not available

– Obtain responses from other agents• is the response useful? (accurate)• is the response in a usable format?• is the response trustworthy?

Real Example: Medical Research• Research at Cincinnati’s Children’s Hospital

– Downloaded several incompatible databases, all translated into RDF

– They then used public domain SW software (from Stanford U and HP labs) to integrate the knowledge

– This was followed by using a ranking algorithm (similar to Google’s) to sort through the integrated knowledge

• through this process, they identified four genes with strong connections that implicated dilated cardiomyopathy

– Similar work is going on at Eli Lilly and the University of Texas Health Science Center

• Is this the same as using the semantic web as described earlier?

Strengths of the Semantic Web• Distributed nature, like the web itself, permits access to any

knowledge anywhere– This also allows an agent to access different sources of the same

knowledge – This also allows an agent to find additional evidence for instance by

resolving the insurance question from the previous example by finding an independent knowledge source

• By allowing anyone to contribute, the knowledge sources have differing perspectives– This provides a richer set of knowledge, although may bring about

contradictions that one must reason over

• By building on top of the WWW, we can utilize knowledge already made available– Although this presents an enormous challenge – how do you convert

syntactic information as currently found on the web to semantic information, by hand or by software conversion?

Application Areas for Internet Agents• Calendar agents and scheduling

– such as the previously covered scheduling example

• Customization of web sites/Recommender agents– sites that tailor your visiting page based on what it thinks you

will like

• Shopper agents– finding the best deals, customizing purchases (for instance,

putting together a vacation by finding the best deals that also match your interests)

• Commerce agents– that help you with on-line investing by bidding for you

• Personal communications and secretaries– as covered earlier, agents that communicate on your behalf

and possibly respond to inquiries

Application Areas Continued• Research tools

– being able to have the search engines do most of the research for you, finding the documents that you are interested in based on content, not key words

• Data mining– using agents to build upon human knowledge by combining the

semantic content of different sites

• Homeland security– for instance by locating terrorist communications via websites

• Sensor interpretation – consider a building which has a variety of sensors, agents work

together to ensure the safety of the building (from fire, vandalism, break ins, etc)

Application Areas Continued• Tool assisting agents

– consider the paper clip from MS Office, lets expand that into something that is really helpful

• a programmer’s assistant that finds errors as you enter them (such as forgetting to declare a variable, or mistyping a reserved word)

• a composition assistant that helps with your prose• a music assistant that helps fill in musical passages as you

compose by computer (for instance, providing a bass or percussion accompaniment)

• a copyright agent which confirms that the contents you are working on do not violate copyrights or plagiarize

• a research aid which finds sources for you (whether on the Internet or elsewhere)

Open Problems• Just about all the problems are still open problems, but

some specific problems being researched include– How to translate from one ontology format to another (for

instance, there are OWL Cyc and Cyc OWL translators)– How to make inferences over the knowledge of an ontology– How to find sources to obtain needed knowledge– How to add semantics to syntactic documents automatically

especially multimedia documents (how do you automatically annotate an image in terms of describing its content?)

• and how to confirm the correctness of any of these four operations– And traditional AI problems applied to the Semantic Web and

agents:• planning• sensor interpretation• learning• natural language understanding and word sense disambiguation• uncertainty handling – can you trust or believe what another agent tells

you?