**6. Conclusion**

The emergence of XOL was inspired by existing ontology and protocol, for example, SHOE, KIF, GFP, OKBC, and so on. XOL is a bridge language, which let the ontology using frame-based approach can be expressed in a simplifier way during the XML file. By the human-readable XML and unified Label limitation, it can use as an ontology exchange language during the cross application, which allows to obey the use of the XOL (in fact is OKBC-Lite) restriction. However, lacking of inferential capability and more logical expression, XOL was replaced by the subsequent ontology language OIL considering the multilanguage and more logic restriction that enable to validate ontology.

This chapter gives an overlook of XOL from the historical development across the different ontology languages. Note that XOL is not the first language in defining the ontology language for exchange date. It merely complements XML syntax and uses a simple frame-based OKBC protocol. However, it still lacks more compatible with multiple ontology protocols and different syntax. Without the more consideration into inference, ontology quickly would replace by stronger ontology system.

We also found that while designing a better widely used ontology language, we should keep a right balance between generality and specificity or between compatibility and limitation. We will focus more on the result comparison between different ontology methods and the humanity background within different languages.
