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Roadmap on extensibility, registries, MIME (and MIME and the web Product Page)

From: Larry Masinter <masinter@adobe.com>
Date: Tue, 13 Dec 2011 11:57:46 -0800
To: "www-tag@w3.org" <www-tag@w3.org>
Message-ID: <C68CB012D9182D408CED7B884F441D4D06121B512A@nambxv01a.corp.adobe.com>
Here's another cut at establishing a framework for "MIME and the Web" product page which I could cut into the preface...
I'm hoping this is stand-alone and "obvious" without additional context. Is it?

As part of

*         ACTION-595 "create a report on Mime and the web"

*         ACTION-636 "Update product page for Mime and the Web"

And likely relevant to

*         ACTION-531 "Draft document on architectural good practice relating to registries"

*         ACTION-350 "Revise .. (references to evolving specs) "

*         ACTION-611 update http://www.w3.org/standards/webarch/protocols<https://www.w3.org/2001/tag/group/track/actions/611> .

Evolution the web, and the role of Registries and MIME

An understanding evolution in the web  needs careful distinction between concepts; for this discussion, the following terms are used:

*         Protocol: a way in which parties interact.

o   Language:  a particular means of interaction by which (using a protocol)  one party sends some data which is then interpreted by the receiver.

o   Protocol element: a small packet of information exchanged in a protocol or used in a language where the meaning of the protocol element in that context is described independently.

*         Implementation: a software agent implementations may use protocols to interact with other agents on the network, and may either read or produce content in one or another language.

*         Standard: in this context, standards are technical specifications which describe  protocols, languages, or protocol elements,  and rules for how implementations of them are expected to behave.

Evolution involves evolution of all of these things in a coordinated fashion:

*         Protocols, languages and protocol elements evolve as implementations of them evolve and are used.

*         Implementations evolve as their implementers of them create or adopt new features; in many cases, that evolution requires evolution or addition to the protocols, languages and protocol elements the implementations use to communicate.

*         Standards evolve as the specifications evolve or extended, both leading implementations (proposing additions or changing) and following implementations where the standard is changed to match implementation behavior.

The value of the Internet and the Web is global communication among unrelated parties. Different implementations need to agree on the protocols, languages, and protocol elements in their communication for them to interoperate.

A standard can allow and promote evolution is to allow for extensibility in some of the protocol elements - the ability to add new values for them that were not part of the protocol or language at the time the standard was written. There are a variety of ways in which this can happen; one commonly used way a standard can allow this kind of evolution is by using a registry.

A registry is a list, maintained by an organization or individual, which lists values of a protocol element and the meaning of that protocol element in the context of the languages or protocols that use it.

MIME is a framework for transmitting content within protocols; one of its most important features is its system of naming languages ("Internet Media Types", informally known as MIME types.)  In particular, there is an Internet Media Type registry.

The "content-type" protocol element (used in the web and email) contains the name of a language (its Internet Media Type) and some parameters; those parameters include a "charset" protocol-element.

HTTP is a protocol. RFC 2616 is a standard that describes it. RFC 2616 allows transmission of data in a language; in that transmission, the language by which the data is to be interpreted is given by the "content-type" protocol element.

HTML is a language, the primary language used in the web. Other "languages" used in the web are JPEG, GIF, CSS, etc.

As the web has evolved, the registry for the Internet Media Type protocol-element has not kept up with the implementations and use within browsers and the HTML language.

There are a number of issues that need to be addressed to help achieve the goal of careful evolution and global interoperability in an evolving world. Those recommendations include attention to the way in which standards allow for extensibility by adding values and new meaning to their protocol elements used within them, guidelines for establishing and using registries, and a clearer model for evolution in a way that a standards organization can lead in the managed evolution of the technology available to its implementations.

There are a number of alternatives and considerations for how extensibility is managed in standards within W3C and IETF that will be examined:

*         Extensibility and choices for allowing extensibility  in otherwise stable standards.

*         Consideration for use of registries.

*         Guidelines for use and maintenance of the MIME registries.
Received on Tuesday, 13 December 2011 20:10:37 UTC

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