Ontology Languages - Case Study Example

Case Study on Ontology Languages For the current consideration on the ontology languages, XOL, RDF, XML, OIL, DAML+OIL and OWL are taken up. Data representation in each one of these languages have been taken up and then compared for ease of use and adaptability. In addition, the benefits of having a hardened format are also considered. Data represented: a. Date of creation of website: http://www.xyz.com is 20 Jul 2006 b. Subject: Semantic web creation c. Creator: J B Conrad d. Email: conrad@xyz.com We will use different languages to represent this simple data. RDF: 20 Jul 2006 Semantic Web Creation conrad@xyz.com XOL: site details An ontology for the website website crdate date subject string creator string email string website http://www.xyz.com website date 20 Jul 2006 subject Semantic web creation creator J B Conrad email conrad@xyz.com XML: http://www.xyz.com J B Conrad Semantic web creation 20 Jul 2006 OIL: websites http://www.xyz.com 20/Jul/2006 J B Conrad Semantic web creation conrad@xyz.com DAML+OIL: http://www.xyz.com J B Conrad conrad@xyz.com Semantic Web Creation May OWL: Comparison of the Ontology languages The ontology specification languages employed to write code include XML, XOL, RDF, OIL and OWL. These languages were used to represent a similar set of data described earlier and the features of these languages are presented below from the simple case that has been taken up. While these languages represent the specifications for the Ontology, they do not represent the real programming languages that are employed like CycL, Ontolingua, F-Logic, etc., 1. XML: This uses a standard syntax laid down already by the W3C. The code is crisp and easy to write. The DTD can be defined the way it is required. However, this does not offer the flexibility of defining standard classes and then making use of the similar structure repeatedly. XML is easy to use in a program though of course, creating XML data which will have semantics in them is not possible with the existing structure of XML. 2. XOL on the other hand, offers all those features that are present in XML as well as in OIL. XOL employs modelling primitives that are in line with OKBC standards. This is based on XML and uses Ontologies to extend the features. Therefore, it is found that the language is supporting some of the insufficiencies in XML like standard class definition and other structure definitions. With these, the data gets verified and the mistakes in the data are avoided. In addition to these, this also supports extensive slot hierarchies. But however, it does not allow definition of relationships extensively. This makes it a weak relationship modeller. XOL is comfortable where only data is to be represented without any major relationship criterion which is hard to find in knowledge systems. 3. RDF makes use of a standard form proposed by W3C as well. This makes up the standard format for data representation using XML or an XML like structure. RDF has a data model which in turn specifies three units: resources, properties and statements. While resources and the properties define a class, statements make the object by assigning values to the same. But RDF does not have a relationship specification. This lacuna is made up using RDF schema specification Language (RDFS) which supports creating and describing ontologies. This again supports only primitive forms of ontology and not a detailed one at that. Therefore, RDFS supports some of is-a and element-of relationships. RDF may not be able to offer a comprehensive ontology definition, however. 4. OIL: Ontology Interchange Language is made for Ontological specifications. Therefore, the specifications and code written using OIL has wider coverage with respect to ontological requirements. It is able to specify quite a detailed structure for data and this structure is reusable subsequently. This also provides information and description for defining relationships. This merges the features of the frame-based languages that originally made up ontology research and the formal semantics and the reasoning services are picked up from the description logics. Since this oriented towards and made for ontology interchange, it satisfies most of the requirements of the ontology research and needs of querying data using ontology. However, ontology is divided into three basic layers: concrete instances, first meta-level or ontological definition and second meta-level or ontological descriptions. While defining and describing ontology, it is needed to define relationships and enumerate axioms that would precisely define the relationships. But in the case of OIL, though the axioms are allowed, they provide only primitive structuring and do not cater to fully to the expressiveness of the language. 5. DAML OIL is based on XML and RDF. This makes it fully compatible with the entire range of XML schema. The reasoning and logic capabilities of the DAML OIL definitions are particularly suited for design and maintenance of ontologies. The failures of the OIL in not supporting natural languages and in providing for full expressiveness have been set right in DAML OIL. This also supports partial interoperability facilities where mapping rules can be defined. 6. OWL on the other hand is defined with all the limitations of these languages taking into consideration. OWL has all the data definition part which it has inherited from RDF and the rest from OIL for the ontological definitions and descriptions. However, as to the limitations of OIL on the description front and on axioms, additional features have been incorporated to ensure that these limitations are also tidied over. Therefore, it is found that all the features looked for ontological languages is found in this. XML DTD XML Schema RDF(S) OIL DAML+OIL OWL Bounded lists X X cardinality constraints X X X X class expressions X X data types X X X defined classes X X Enumerations X X X X Equivalence X X Extensibility X X X X formal semantics X X Inheritance X X X X Inference X (Partly) X local restrictions X X Qualified constraints X X Reification (date stamping) X X Insufficiencies of OWL A number of insufficiencies have been indicated in the main paper. In addition to those, there are a number of future enhancements that are needed to ensure that OWL stays in line with the developments happening on the web. 1. From the cases listed above, including OWL, none of the other Ontology Languages support or work on instant messaging networks. One of the major growth areas for web is in the instant messaging network. Most of the data bases do not take into consideration the emotions that line these IM networks. Web ontology languages have not given this area any special thought. Though, in the RFC 2779 of IETF, there is an expressed standard for Internet Messaging and Presence Protocol (IMPP) which should possibly stabilise the messaging standards (Yiling Lu 2003). This could eventually lead to handling ontology issues with the messaging platform for queries on the fly. Standard IM software do not cater to the needs of the Ontology systems. 2. On the query front, Web Ontology Languages proposed such as the OWL-S, do not effectively support all the SQL operations. This includes features such as updating and deleting metadata and data resources. This would have to ensure that the Meta data once deleted should also update all other sub classes that are adopting the Meta data so formed. This is primarily, the referential integrity check that the language has to support (Ahmet Soydan Bilgin Aug 2003). This makes the Ontology language still primitive with respect to handling metadata effectively; adding or updating them on the fly. 3. Web Ontology falls short on many issues connected to Natural Language Processing. As could be seen from the examples discussed so far, the Ontology languages are not tuned for natural language processing (Marjorie McShane et al. 2005). References 1. Ahmet Soydan Bilgin (Aug 2003) Semantic Web Services Query and Manipulation Language for Quality attributes of Web Services, North Carolina State University, available at: http://www.lib.ncsu.edu/theses/available/etd-08182003-234629/unrestricted/etd.pdf 2. Yiling Lu (2003) Roadmap for Tool Support for Collaborative Ontology engineering, University of Victoria, available at: http://www.cs.uvic.ca/chisel/thesis/YilingLu.pdf 3. Marjorie McShane, et al. (2005) An implemented Integrated Approach to Ontology Based NLP and Interlingua, ILIT University of Maryland, Baltimore County, available at: http://ilit.umbc.edu/ILIT_Working_Papers/ILIT_WP_06-05_Controlled_Langs.pdf Annexure OIL XML DTD Schema RDF Schema Resource The class resource, everything. type The subject is an instance of a class. Class The class of classes. subClassOf The subject is a subclass of a class. subPropertyOf The subject is a subproperty of a property. Property The class of RDF properties. comment A description of the subject resource. label A human-readable name for the subject. domain A domain of the subject property. range A range of the subject property. seeAlso Further information about the subject resource. isDefinedBy The defininition of the subject resource. Literal The class of literal values, eg. textual strings and integers. Statement The class of RDF statements. subject The subject of the subject RDF statement. predicate The predicate of the subject RDF statement. object The object of the subject RDF statement. Container The class of RDF containers. Bag The class of unordered containers. Seq The class of ordered containers. Alt The class of containers of alternatives. ContainerMembershipProperty The class of container membership properties, rdf:_1, rdf:_2, ..., all of which are sub-properties of 'member'. member A member of the subject resource. value Idiomatic property used for structured values. List The class of RDF Lists. nil The empty list, with no items in it. If the rest of a list is nil then the list has no more items in it. first The first item in the subject RDF list. rest The rest of the subject RDF list after the first item. Datatype The class of RDF datatypes. XMLLiteral The class of XML literal values. People.owl Read More