Data heterogeneity in the public sector is a serious problem and remains to be a key issue as different naming conventions are used to represent similar data labels. The e-government effort in many countries has provided a platform for government entities and their business partners to exchange data through Information Communication Technologies (ICT) and standards such as RosettaNet (B2B data exchange standard), EDIFACT (Electronic Data Interchange for Administration, Commerce, and Transport), XML (Extensible Mark-up Language) and EDI (Electronic Data Interchange). However, e-government efforts have not really resolved data heterogeneity problems significantly due to limitation of these standards. One such limitation is the inability of data inheritance. In order to solve this problem with emphasis on Service Oriented Architectures (SOA) and Web Services, a semantically enriched web service for the public sector is needed. Thus we propose an ontology-based solution which allows data inheritance and polymorphism. This goal of this paper is to show how heterogeneous e-government documents can be semantically matched. We propose a shared hierarchical knowledge repository approach and a detailed process methodology for semantic mediation. A two-part semantic mediation approach using SRS (Semantic Relatedness Scores) and SWRL (Semantic Web Rule Language) is highlighted. Both measures are complimentary and provide the semantics necessary for resolving schema heterogeneity. Our approach incorporates a rule-based engine that reads and executes SWRL rules (i.e. RacerPro). We also adopted several tools for proof-of-concept such as Protege (i.e. ontology editor) and JESS (Java Expert Shell System).