On RDF of Semantic Web

Abstract

The semantic web is initiated to provide machine accessible meaning for its constructs. Semantic web relies on Resource Description Framework (RDF), which is a standard model to interchange data on the Web. One of the representations of RDF is graph data model which, is known as RDF_graph model. One of the goals of the semantic web is to publish the vast quantities of data that is stored in the Relational Databases (RDB) for computer processing. In order to integrate RDB into semantic web applications, RDB should be represented as RDF_graph data model, which is fundamental problem for developing the semantic web in the recent decade. Most of academic works that have been proposed to represent RDB as RDF_graph data model are relying on converting the data that is stored in the relational model not the schema. Furthermore, none of the existing models proposed a formal graph representation for RDF_graph that corresponds to RDB schema to satisfy the integrity constraints, functional dependencies, normalization, and data semantics that are defined on the schema. Moreover, a formal representation of RDF_graph that corresponds to RDB schema facilitates the data conversion and allows graph connectivity which is important for querying and editing RDF using different traversal algorithms. One of the most special classes of database schema, called acyclic database schema, was introduced in the last decades. This class is preferred in order to minimize the time of answering query and decrease its space efficiently access paths. Also the result of answering query will be reduced specially in the case of representing RDB as graph data model. This thesis introduces a new type of cyclicity in hypergraphs through the notions of Quasi α-cycle(s) and the set of α-nodes in hypergraphs, which are based on the existence of an α–cycle(s). Then, it is proved that a hypergraph is acyclic if and only if it does not contain any α-nodes. Moreover, the thesis aims to propose a model to introduce a Backward and Forward hypergraph (BF-hypergraph) representation for RDF_graph that corresponds to acyclic/cyclic RDB schema according to its set of functional dependencies. The BF-hypergraph is an appropriate model for representing the set of functional dependencies of RDB, since the domain and codomain of the functional dependency may contain more than one attribute.