Java Semantic Network Programming Series 2: Ontology

What is ontology?

The OWL ontology is used to model domain knowledge. It is the core element of semantic web.

Ontology element Overview

On the web, the ontology is generally stored as a document. The document composition is as follows:

A. ontology header:

The first is a resource used to describe the ontology itself. The header describes the ontology, which generally contains comment, label, and version information.

B. Classes and individuals

An owl class is a special resource that describes a set of resources with common features or similar aspects. An individual (individual) is also a resource. It is a class member representing an instance of this class.

For example, Person is a class, Ryan
Andrew is an instance of it.

C. Attributes

An attribute in OWL is a resource that acts as a predicate in the statement describing an individual. There are two main types of attributes in OWL: object attributes are used to connect a group of individuals with another group of individuals, and data type attributes are used to connect individual and text. For example, Ryan has the hasName data type attribute.
An object property like Konw connects Ryan and Andrew.

D. Annotation

Annotation is actually an attribute. It is similar to other attributes, but it has no associated semantics. It is mainly used for display on the interface.

E. Data Type

The data type in OWL indicates the value range of the data value. Integer, string, and time are common data types.

 

Thing And nothing

There are two basic classes in owl: thing and owl: nothing. All classes are derived from these two classes. Resource owl: thing indicates all individual classes, and all resources that act as class instances are essentially members of owl: thing. Owl: nothing indicates an empty class, that is, a class without a member.

 

Attribute definition and Value

Owl allows the use of rdfs: domain and rdfs: range to describe the relationship between attributes and classes or between the predefined domain and the Value domain before the attributes and data types.

Domain: specifies the type of the subject in the assertion.

Range
: Specifies the object type in the assertion.

Example:

Ryan Andrew is two individual. Their domain belongs to Person, and their hasname attribute's range
It is a string.

 

Description attribute

That is, attributes with specific meanings.

1 rdfs: subpropertyof

Like a class, you can use the subpropertyof attribute to classify attributes. To explain the connotation of the sub-attribute relationship, assume that the attribute hasNickName subpropertyof hasName is declared in the ontology. This assumption declares the fact:

HasNickName
Is a special feature of hasName.

Any two resources associated with hasName can be associated with hasNickName.

 

2. Inverse attribute

A property declares a directed link. The direction of the link is from the defined domain to the value domain or from the subject to the object. Sometimes there is a link in one direction and another link is hidden.

Owl allows the use of the owl: inverseof attribute to declare one attribute as the inverse attribute of another. Assume that the following statements declare hasChild and
HasParent is reversible, so the fact is true:

If there is a statement (individualA hasChild individualB), it will be (individualB hasParent individualA)

 

3. Non-Intersecting attributes

Owl provides a pair of structures that specify two attributes as non-intersecting. When we say that two attributes do not overlap, the following facts exist:

The subject and object of the two attributes cannot be identical.

For example, hasFather and
HasMother

 

4 Key

The concept of keys is introduced in Owl. The Owl contains the owl: hasKey attribute, which is used to associate a specific class with an attribute set.

 

5 Data Types

The data type is used to indicate the value range of the data value identified by the Uri.