Network Working Group P. Kyzivat Internet-Draft Huawei Updates: 5234 (if approved) January 3, 2013 Intended status: Standards Track Expires: July 7, 2013 ABNF Extensions for Importing and Scoping draft-kyzivat-abnf-import-00 Abstract This document proposes extensions to the ABNF defined in [RFC5234] to support importation of ABNF from other documents, and multiple naming scopes for rulenames. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on July 7, 2013. Copyright Notice Copyright (c) 2013 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Kyzivat Expires July 7, 2013 [Page 1] Internet-Draft ABNF Import January 2013 1. Introduction The intent of this proposal is to better support current practice where one draft or RFC extends the ABNF from another draft or RFC, or references ABNF rules defined elsewhere when defining something new. Currently that is done using comments that identify the source of the referenced definitions. Formally processing this requires manual actions to cut and paste definitions from multiple documents to create a single ABNF source that can be processed for formal tools. With the proposed changes, it will be possible to build ABNF tools that automatically extract the required definitions. The changes that support this are: o A way to assign a name to a rule list within a document This allows multiple independent groups of rules to be defined within a single document and referenced independently. For flexibility, nesting of named rule lists is permitted. o A way to reference a rule defined in a named collection of rules o A way to import rule definitions from another document The reference identifies the document and may name a specific named rule list within that document. When importing a named rule list, it may be imported with or without the name. The definitions are copied into 2. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. 3. Extensions to ABNF Syntax The following are additions to the ABNF for ABNF defined in [RFC5234]. Kyzivat Expires July 7, 2013 [Page 2] Internet-Draft ABNF Import January 2013 rulelist =/ 1*( named-rulelist / rulelist-import / rule/ (*c-wsp c-nl) ) ; this is really a backward compatible replacement definition named-rulelist = rulelist-name *WSP "{" rulelist "}" c-nl rulelist-name = rulename rulelist-import = (basic-import / named-import) c-nl basic-import = "@" docname ; imports all the ABNF from the named document docname = char-val ; format and resolution of the document from the docname ; is defined by the specific tools used. ; At least common URI types should be supported ; E.g. "urn:ietf:rfc:5234", ; "urn:ietf:id:draft-ietf-foo-bar-01", ; "file:foo.xml" named-import = rulelist-name basic-import ; (E.g. CORE@"urn:ietf:rfc:5234") ; This is shorthand for importing into a new named ; rulelist with the given name. element =/ scoped-rulename scoped-rulename = 1*(rulelist-name ".") rulename 4. Import Semantics Importing logically replaces the import statement with text from the imported document. Importing may be done in two ways: o The simply inserts all the ABNF from the referenced document. o The is similar, but does the import within a new . This is just syntactic sugar, but is convenient. E.g. the following: CORE@"urn:ietf:rfc:5234" Kyzivat Expires July 7, 2013 [Page 3] Internet-Draft ABNF Import January 2013 is equivalent to: CORE { @"urn:ietf:rfc:5234" } Note that if the imported rules contain references to rules that are not imported, then the importing document must provide definitions for those. For now, the ABNF syntax of ABNF defines a docname as a string without further syntax. Interpretation of the docname is deferred to the ABNF processing tools. I propose that this should at least support common URI formats, including the urn:ietf format for rfcs and ids. It may also be expedient to support some more concise syntax for ietf documents. The intent is that the import statements only import the ABNF definitions from the referenced document, ignoring any content that is not ABNF. This is so that ABNF from RFCs and drafts can be referenced directly. The xml2rfc notation should be sufficient to support this. If multiple abnf artwork elements are present they should simply be concatenated to form one logical document to be imported. 5. Scoping of Names A document containing ABNF has an implicit outermost scope. Each scope has a symbol table for rules and named rulelists defined within that scope. The appearance of a with a particular creates a nested scope with that name within the enclosing scope's symbol table. Once a named rulelist has been closed it may not be reopened. (This ensures that redefinition of a named rulelist is an error, preventing a class of errors.) An element consisting of a is resolved within the symbol table of the scope where it is found. If not found, resolution is attempted successively in each enclosing scope. An element consisting of a is resolved as follows: o The leftmost component of the (the first ) is resolved first. Kyzivat Expires July 7, 2013 [Page 4] Internet-Draft ABNF Import January 2013 o It is resolved by looking within the symbol table of the scope where it is found. If not found, resolution is attempted successively in each enclosing scope, and must resolve to a . o Then the next component ( or ) is resolved within the symbol table of that rulelist. This continues until the last component has been resolved. I'm undecided whether it should be possible to have both a rule and a rulelist with the same name in the same scope. It is important to maintain the order independence of rule definitions that exists with prior definitions of ABNF. (It must be possible to reference a rule in a named rulelist that is defined later.) 6. IANA Considerations Don't think so. 7. Security Considerations Security is truly believed to be irrelevant to this document. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC5234] Crocker, D. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, January 2008. 8.2. Informative References Author's Address Paul Kyzivat Huawei Email: pkyzivat@alum.mit.edu Kyzivat Expires July 7, 2013 [Page 5]