ProtégéProtégéAn Environment for An Environment for

Knowledge-Based Systems Knowledge-Based Systems DevelopmentDevelopment

Haishan LiuHaishan Liu

Outline

Things will be covered The evolution of Protégé and the

underlying driven idea Major features of different versions of

Protégé Things will not be covered

The detailed mechanisms and algorithms of the implementation

What is Protégé

The Protégé system is an environment for knowledge-based systems development

From a single tool to reduce the knowledge-acquisition bottleneck to a general-purpose environment for knowledge modeling

The classical model of expert system development

Difficulties in the classic model

The knowledge engineer is involved in all phases of system construction characterize the reasoning tasks identify the major domain concepts categorize the type of knowledge identify the reasoning strategies used by experts, define an inference structure for the resulting application, and formalize all this knowledge in a generic and reusable

way. domain experts are seen simply as resources for

knowledge engineers to draw upon.

An early view: expert system shell

Reuse of knowledge Base

•Knowledge acquisition is carried out by the knowledge engineer.•The introduction of a knowledge engineer in between could lead to errors and misunderstandings. •Time-consuming

Domain expert

Protégé Ancestry: Oncocin and Opal

Information-partitioning hypothesis

structural domain concepts ① domain knowledge ② case data ③

① ②

③

Advantage of Opal/Oncocin architecture

Actual tools developed for knowledge acquisition

The domain experts directly build the knowledge base reduce the likelihood of errors Streamline knowledge base construction

Protégé-I

generalization of the Oncocin/Opal architecture

Assumptions of Protégé-I

Problem specific KB Only works well on certain PSMs

Problem-solving method (PSM) provides semantics of KB No formalization of the knowledge model

Atomic PSM and KB Self-contained KB (no reference to the others) Single monolithic PSM

Summary of Protégé-I

Generating knowledge-acquisition tools from structured meta-knowledge

Neither reusable nor general purpose Problem-specific KB Lacking formal semantics

Protégé-IIreusable problem-solving methods.

A problem-solving method could be developed independently from the knowledge base.

PSMs were generic algorithms that could be used with different knowledge bases to solve different real-world tasks. constraint satisfaction Classification Planning Bayesian inference

Problem-solving knowledge automates specific tasks

Domain knowledge + Problem-solving method

Intelligent behavior

Protégé-IIReusable problem-solving methods

Developing Knowledge-based Systems with Protégé-II

Developing or reusing a problem-solving method

Defining an appropriate domain ontology Generating a knowledge-acquisition tool Building a knowledge base using the tool Integrating these components into a

knowledge-based system defining mappings between problem-solving

methods and specific knowledge bases.

Three classes of ontologies

Domain ontologies (reusable) define the concepts related to an application

domain (e.g., different symptoms, anomalies, and remedies)

Method ontologies (reusable) specify the data requirements of the problem-

solving methods (i.e., the input and output structure of each method)

Application ontologies (application specific) define the concepts that are specific to a

particular application or implementation.

Protégé-II components for building knowledge bases.

“Downhill Flow” Model

Knowledge engineer

Domain Expert

Integrating the Components of a Knowledge-Based System—Mappings

KB and PSM are developed separately PSM may not match KB

Use mapping relations to connect KB and PSM Marble – a special KA tool to build mapping

relations A generic mapping interpreter producing

adapted view of KB to PSM

Summary of Protégé-II

Reusable PSMs as components Adoption of ontology Generation of KA-tools from any

ontology “Downhill Flow” assumption of class

over instance

Protégé/WinBesides the re-implementation

The use of modular ontologies, via an ontology inclusion mechanism build large knowledge bases by “gluing” together

a set of smaller, modular ontologies scale to large problems better than monolithic

ontologies A more integrated, streamlined set of tools A more custom-tailoring knowledge-

acquisition tool

Protégé-2000significant augmentations

Underlying knowledge model A single unified application A plug-in architecture

The Protégé-2000 Knowledge Model

Protégé-I hand-coded Lisp object

Protégé-II and

Protégé/Win

a simple frame-based model provided by CLIPS

Protégé-2000 OKBC protocol

Retrospect

Open Knowledge Base Connectivity (OKBC)

Standard mechanism to access knowledge bases stored as “frames” of classes and attributes

Adopted by several well-known knowledge-representation systems (Ontolingua, LOOM)

Will allow Protégé-2000 to be used as an ontology- and knowledge-editing system for any OKBC-compliant server

OKBC – cont’d

OKBC specifies a knowledge model of KRSs with KBs, classes, individuals, slots, and facets

It also specifies a set of operations based on this model find a frame matching a name enumerate the slots of a frame delete a frame

An application uses these operations to access and modify knowledge stored in a OKBC-compliant KRS.

The OKBC Knowledge Model

Constants Frames Slots Facets Classes Individuals knowledge bases

Frames, slots and facets

Frame primitive object that represents an entity in the

domain of discourse Class Frame, Individual Frame

Slot Binary relation associate to a frame (describing

the property of the frame) Facet

Constraints on the slot

The plug-in architecture of Protégé-2000

The OntoViz tab plug-in

A Protégé-2000 KA tool for entering rules for monitoring nuclear power plants

Elements of Protégé-2000

Slots as first-class

objects

Slots as first-class

objects

Classes andclass

hierarchy

Classes andclass

hierarchy

Facetsstandard anduser-defined

Facetsstandard anduser-defined

InstancesInstances

Customizableinstance

forms

Customizableinstance

forms

Easybrowsing

Easybrowsing

Means to

viewlargedata sets

Means to

viewlargedata sets

CustomwidgetsCustomwidgets

Domain-specific

tabs

Domain-specific

tabsComponentsfor building

knowledge-basedapplications

Componentsfor building

knowledge-basedapplications