Query + Metadata + Logic = Metalog.
Massimo Marchiori, Janne Saarela · 1998
This paper will demonstrate how a new querying language, Metalog, allows users to write inference rules and queries in English-like syntax. We will demonstrate how these reasoning rules have equivalent representation both as RDF descriptions and as logic programs. We will also show how an automated compilation between these translations is possible. For the sake of clarity, here we will just give an overview of the system, trying to avoid technicalities and cumbersome details. Query Languages In general, query languages are formal languages to retrieve data from a database. Standardadized languages already exist to retrieve information from different types of databases such as Structured Query Language (SQL) for relational databases and Object Query Language (OQL) and SQL3 for object databases. Semi-structure query languages such as XML-QL [3] operate on the document level structure. Logic programs consist of facts and rules where valid inference rules are used to determine all the facts that apply within a given model. With RDF, the most suitable approach is to focus on the underlying data model. Even though XML-QL could be used to query RDF descriptions in their XML encoded form, a single RDF data model could not be correctly determined with a single XML-QL query due to the fact that RDF allows several XML syntax encodings for the same data model. The Metalog Approach RDF provides the basis for structuring the data present in the web in a consistent and accurate way. However, RDF is only the first step towards the construction of what Tim Berners-Lee calls the "web of knowledge", a World Wide Web where data is structured, and users can fully benefit by this structure when accessing information on the web. RDF only provides the "basic vocabulary" in which data can be...