Up to now, so you’re able to establish the sentence structure out-of RIF-FLD we made use of “mathematical English,” a different types of English getting interacting statistical significance, examples, etc. The next factors in regards to the EBNF notation might be stored in mind:
- The latest sentence structure out of RIF-FLD utilizes the brand new signature procedure which can be perhaps not framework-totally free, so EBNF will not simply take so it syntax correctly. This is why, the fresh new EBNF grammar describes a strict superset out of RIF-FLD (not absolutely all algorithms which might be derivable utilizing the EBNF grammar is actually well-formed).
- The EBNF syntax is not a concrete syntax: it does not address the details of how constants (defined in [RIF-DTB]) and variables are represented, and it is not sufficiently precise about the delimiters and escape symbols. White space is informally used as a delimiter, and is implied in productions that use Kleene star. For instance, TERM* is to be understood as Name Term . Term, where each ‘ ‘ abstracts from one or more blanks, tabs, newlines, etc. This is done intentionally since RIF’s presentation syntax is used as xmeets login a tool for specifying the semantics and for illustration of the main RIF concepts through examples.
- RIF defines a real sentence structure simply for investing rules, and therefore syntax try XML-based, acquired because the an elegance and you will serialization of the EBNF syntax through the fresh new demonstration-syntax-to-XML mapping to own RIF-FLD.
Keeping these in mind, the fresh new EBNF grammar can be seen since just an intermediary anywhere between brand new statistical English and also the XML. But not, in addition gets a brief look at the new syntax from RIF-FLD and therefore they can be handy to have dialect musicians and profiles the exact same.
Per RIF-FLD formula and you may title can be prefixed having one to elective annotation
The RIF-FLD presentation syntax does not commit to any particular vocabulary and permits arbitrary sequences of Unicode characters in constant symbols, argument names, and variables. Such sequences are denoted with UNICODESTRING in the above syntax. Constant symbols have this form: "UNICODESTRING"^^SYMSPACE, where SYMSPACE is a ANGLEBRACKIRI or CURIE that represents the identifier of the symbol space of the constant. UNICODESTRING, ANGLEBRACKIRI, and CURIE are defined in Section Shortcuts for Constants in RIF’s Presentation Syntax of [RIF-DTB]. Constant symbols can also have several shortcut forms, which are represented by the non-terminal CONSTSHORT. These shortcuts are also defined in the same section of [RIF-DTB]. One of them is the CURIE shortcut, which is used in the examples in this document. Names are Unicode character sequences that form valid XML NCNames [XML-Names]. Variables are composed of Names prefixed with a ?-sign.
, which is used in several places in the grammar, is a non-terminal whose definition is left to the dialects. It is intended to specify the protocol by which external sources, remote modules, and imported RIF documents are located. This must include the basic form
The symbols NEWCONNECTIVE, NEWQUANTIFIER, NEWAGGRFUNC, and NEWTERM are RIF-FLD extension points. They are not actual symbols in the alphabet. Instead, dialects are supposed to replace NEWCONNECTIVE, NEWQUANTIFIER, and NEWAGGRFUNC, by zero or more actual new symbols, while NEWTERM is to be replaced by zero or more new kinds of terms. Note that the extension point NEWSYMBOL is not shown in the EBNF grammar completely avoids mentioning the alphabet of the language (which is infinite).
IRIMETA, for identification and metadata. IRIMETA is represented using (*. *)-brackets that contain an optional rif:iri constant as identifier followed by an optional Frame or cones as metadata. One such specialization is '"' IRI '"^^' 'rif:iri' from the Const production, where IRI is a sequence of Unicode characters that forms an internationalized resource identifier as defined by [RFC-3987].