Object Modeling of Ontologies and Object models in Object Oriented Software Engineering
The object-oriented model is based on a collection of objects. An object contains values stored in instance variables within the object. Thus objects contain objects to an arbitrarily deep level of nesting. Attributes/properties: objects will have at least one attribute. Possible slot types are primitive types (integer, boolean, string etc.), references to other objects (modeling relationships) and sets of values of these types. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Method/Operations: They are attached to classes or slots and contain meta information, such as comments, constraints and default values. Relationship/relations: they represent the relation between objects/classes from objece model (KB). Major classes of relations exist: relations combining labels(the name we tend to give to things) and concepts(the things themselves) and concepts and relations combining concepts (the part-whole relation).
Objects that contain the same types of values and the same methods are grouped into classes. A class may be viewed as a type definition for objects. Analogy: the programming language concept of an abstract data type. The only way in which one object can access the data of another object is by invoking the method of that other object. This is called sending a message to the object. Internal parts of the object, the instance variables and method code, are not visible externally or some researchers called it as black box.
Object/Class represent the tangible things. For example, an object representing a bank account. The object contains instance variables number and balance. The object contains a method pay-interest which adds interest to the balance. Under most data models, changing the interest rate entails changing code in application programs. In the object- oriented model, this only entails a change within the pay- interest method. In commonly-known object-oriented data models attributes and associations are not defined with the class specification itself. Instead, class properties are first-class primitive themselves .
One approach for implementing objects is to have a class, which defines the implementation for multiple objects. A class defines what types the objects will implement, how to perform the behavior required for the interface and how to remember state information. Each object will then only need to remember its individual state. Although using classes is by far the most common object approach, it is not the only approach (using prototypes is another approach) and is really peripheral to the core concepts of object-oriented modeling.
Unified Modeling Languages (UML) is well known and widely used object modeling that consist of concepts /entitypes/classes in a specification hierarchy, the description of concepts by attributes which have range and relationship between concepts. UML defines several types of diagram that can be used to model the static and dynamic behaviors of a system. A UML object diagram does not define a standard set of primitive types for attributes and operation declarations; however, Object Constraint Languages (OCL) does and it is proposed that these be used for ontology modeling with UML Model an ontology as a static model consisting of a class diagram to depict the classes in the domain and their relationships, an object diagram to show particular named instances of those classes.
Conceptual (or Ontology) modeling deals with the question on how to describe in a declarative and abstract way the domain information of an application, its relevant vocabulary, and how to constrain the use of the data. Modeling languages like UML and Object Data Management Group (ODMG) have been developed for object oriented models in software engineering. Common to all of these newer models is the arrangement of concepts/entitytypes/classes in a specialization hierarchy, the description of concepts by attributes which have ranges and relationships between concepts. Concepts, relationshiptypes and attributes abstract from concrete objects or values and thus describe the schema (the ontology). On the other hand concrete objects populate the concepts, concrete values instantiate the attributes of these objects and concrete relations instantiate relationships.
