**3.3 Slots on slots**

Slot is common property of each class or instance. The attribute "Documentation" of class has an introduction to this class. When it comes to the specific KB, slot may divide into "own slot" in this KB or "template slot" inheriting from class.

Slots on slots, as shown in **Table 2**, are the several restrictions or declarations defined to this slot. Although it may be inherited from other KB or class, restriction or declaration on slots in this XOL file is exclusive.


**Table 1.** *The classes of XOL [2].*


#### **Table 2.**

*The slots on slots of XOL.*


#### **Table 3.** *The facet of XOL.*

#### **3.4 Acceptable facet**

Different with slots on slots, facet is a restriction on the value of slot of individual. For instance, facet VALUE-TYPE and facet NUMERIC-MINIMUM describe the type of value of a slot and the minimum of value of a slot. **Table 3** is the acceptable facet defined in OKBC-Lite.

**43**

*Ontology Language XOL Used for Cross-Application Communication*

mation (name, type of DB, in which package, etc.) about this KB. <Module> /\*Every XOL file will start with a module mark \*/

<Documentation>String-type description</Documentation>

[Other-option-slot] (Subclass-of | instance-of | etc.)

<Name>name of own slot or template slot</name> <Documentation>description</documentation>

<value-type (or facet in **Table 3**)>...</value-type>

be combined and on how they can be used to define a class.

<Domain (or other slots on slots in **Table 2**)>.</Domain>

Every XOL file must start with the following XML tab in the beginning. <? xml version="1.0"?><!DOCTYPE module SYSTEM "module.dtd">

As the whole KB's first description, 'module section' will illuminate some infor-

The second section is 'class section.' In this section, we will introduce all these KB's classes or inherit from other class by the tag 'subclass-of' or 'instance-of.'

The third section is 'slot section,' which declares all slots in the class and slots existing slot value in an individual, such as the class-name, class-documentation,

The last section generally is 'individual section.' It contains all instances and their values in each slot. Also, it declares restriction of value of slot and slot-values.

At last, remember that XOL file must use </model> to note the ending.

Framework representation is to express the concepts, instances, classes, and relationships used in ontology in the form of framework. XOL is such a framework method-based ontology representation language. Unlike the rich expressions in logic-based approach, XOL leads to the deficiency in reasoning ability. The main differences stem from the fact that frames generally provide quite a rich set of primitives but impose very restrictive syntactic constraints on how primitives can

Due to the deficiency of XOL in grammatical reasoning and the continuous development of DL notation, another new ontology interactive language OIL is defined [9]. It is not only an ontology description language but also a frame-based web language and an XML and RDF compatible ontology language. Its appearance unifies the characteristics of traditional ontology language and endows the new object into the inference layer.

*DOI: http://dx.doi.org/10.5772/intechopen.91385*

<Name>name of this KB</Name>

<Name>name of class</Name>

<kb-type>which existing kb type</kb-type> <package>self-defined package name</package>

**4. XOL example**

<Class>

</Class>

<Slot>.

</Slot>

<Individual> <Name></name>

<Slot-values> <Name>... </name> <Values>...</values>

</slot-values> </individual>

<instance-of></instance-of>

**5. Future developments: OIL**

and other-option slot.

Facet can also divide into two parts:

