PrF UG glossary

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This Glossary defines terms used in this description of Protege. It is not meant to be an exhaustive list of terminology associated with object-oriented modeling.

Abstract Class

An abstract class cannot have instances. It is identified with a hollow round icon (e.g., classes_class.abstract or classes_class.metaclass.abstract).

Allowed Classes

A constraint on the values of a type-instance slot. The value of the slot can only be an instance of the class (or any of its children) in the Allowed Classes list.


The program that combines the Protege knowledge base with a problem-solving method, so that end users can use a Protege knowledge base to solve a problem.


A type of slot with a true or false value. Boolean slots appear as checkboxes in Protege-Frames. A checked box signifies a true value.

Browser Key

The browser key of a class is one of its slots whose value is displayed when instances of this class are referred to by other instances' forms.


A slot facet that describes whether the slot has just one value (single) or more than one value (multiple). In Protege-Frames, Single is the default.


An abstract representation of a concept in a domain as a collection of related classes. For example, a medical model might have protocol, guidelines, and patient data as classes. A class appears with a round gold icon in Protege-Frames (e.g., classes_class, classes_class.abstract, classes_class.metaclass, or classes_class.metaclass.abstract). A class can have a set of slots that represent the attributes of the class.

Classes Tab

The Protege-Frames part used to create, view, revise, and save classes.

Concrete Class

Concrete classes can have instances. They are identified by a solid round icon (e.g., classes_class or classes_class.metaclass).

Direct Slot

A slot which is attached directly to a class (in contrast to a slot which is inherited).


A particular field of knowledge, such as breast cancer.


An attribute of a slot. Some facets depend on the value of the type facet. For example, an integer slot type has facets for Minimum and Maximum.


A positive or negative real numeric value (e.g., 1.0, 3.4e10, -0.3e-3), used as a slot value.

Forms Tab

The Protege-Frames part used to create the forms for acquiring instances of classes. It may also be used to view, revise, and save the forms.


A frame is a primitive object that represents an entity in the domain of discourse. In Protege-Frames, a frame can represent a class, slot, facet, or instance.


A parent-child (superclass-subclass) relationship between two classes. A child (subclass) inherits the slots of its parent classes (superclasses).

Inherited Slot

A slot that is attached to a class via inheritance from a superclass.

Instance (KB value)

Concrete occurrence of information about a domain that is entered into a knowledge base. For example, Fran Smith might be an instance for a Name slot. An instance is entered via a form generated by Protege-Frames.

Instance (slot type)

A type of slot whose value is the instance of a class.

Instances Tab

The Protege-Frames part used to acquire instances of classes. It may also be used to view, revise, and save the instances.


A positive or negative whole number (e.g., 1, 2, -4), used as a slot value.

Knowledge-acquisition tool

A tool used to build a knowledge base by acquiring instances. In Protege-Frames, the forms comprise the KA tool.

Knowledge base (KB)

A set of instances of classes which may be used by PSMs.

Knowledge-based system

A computer system that includes a knowledge base about a domain and programs that include rules for processing the knowledge and for solving problems relating to the domain.


A template; that is, a class whose instances are themselves classes.


A model of a particular field of knowledge - the concepts and their attributes, as well as the relationships between the concepts. In Protege-Frames, an ontology is represented as a set of classes with their associated slots.

PAL (Protege Axiom Language)

A plugin toolset that comprises engines for checking constraints and running queries on knowledge bases, as well as a set of useful user interface components.

.pins file

A Protege-Frames file in CLIPS format that contains instances.

.pont file

A Protege-Frames file in CLIPS format that contains an ontology.

.pprj file

A Protege file that contains a project. A project file contains the customized form information and references to external sources of the domain information.

Problem-solving method (PSM)

A computer program that is used in conjunction with a knowledge base to answer questions or solve problems.


An attribute of a class. For example, a physician class might have name, title, and phone number as slots.

Slot Type

A slot facet that identifies the kind of values a slot may have - any, boolean, float, instance, integer, string, or symbol.

Slots Tab

The Protege-Frames part that allows you to create, view, edit, and delete slots.


An enumerated list of slot values, such as red, blue, green.

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