This document develops RIF-BLD (the Basic Logic Dialect of the Rule Interchange Format) based on a set of foundational concepts that are supposed to be shared by all logic-based RIF dialects.
From a theoretical perspective, RIF-BLD corresponds to the language of definite Horn rules (see Horn Logic) with equality and with a standard first-order semantics. Syntactically, RIF-BLD has a number of extensions to support features such as objects and frames, internationalized resource identifiers (or IRIs, defined by RFC 3987 [RFC 3987]) as identifiers for concepts, and XML Schema data types. The last two features make RIF-BLD into a Web language. However, it should be kept in mind that RIF is designed to enable interoperability among rule languages in general, and its uses are not limited to the Web.
RIF-BLD is defined in two different ways. First, it is defined as a specialization of RIF-FLD, the RIF Framework for Logic-based Dialects; it is a very short description, but it requires familiarity with RIF-FLD. RIF-FLD provides a general framework -- both syntactic and semantic -- for defining RIF dialects. With this framework, one can extend RIF-BLD with default negation, higher-order features, and so on. Then RIF-BLD is described independently of the RIF Framework, for the benefit of those who desire a quicker path to RIF-BLD and are not interested in the extensibility issues.
One fragment of RIF is called the Condition Language. It defines the syntax and semantics for the bodies of the rules in RIF-BLD. However, it is envisioned that this fragment will have a wider use in RIF. In particular, it will be used as queries, constraints, and in the conditional part in production rules (see RIF PRD), reactive rules, and normative rules.
The current document is the third draft of the RIF-BLD specification. A number of extensions are planned to support built-ins, additional primitive XML data types, the notion of RIF compliance, and so on. Tool support for RIF-BLD is forthcoming. RIF dialects that extend RIF-BLD in accordance with the RIF Framework for Logic Dialects will be specified in other documents by this working group.