RFC 2077 (rfc2077) - Page 2 of 13

The Model Primary Content Type for Multipurpose Internet Mail Extensions

RFC 2077                Model Primary MIME Types            January 1997


1. Overview

   This document will outline what a model is, show examples of models,
   and discuss the benefits of grouping models together.  This document
   will not directly deal with the intended subtypes since those will be
   covered by their separate registrations.  Some immediately expected
   subtypes are listed in section 7.

   This document is a discussion document for an agreed definition,
   intended eventually to form a standard accepted extension to RFC
   2045.  We are also targeting developers of input/output filters,
   viewer software and hardware, those involved in MIME transport, and
   decoders.

2. Definition of a model

   A model primary MIME type is an electronically exchangeable
   behavioral or physical representation within a given domain.  Each
   subtype in the model structure has unique features, just as does each
   subtype in the other primary types.  The important fact is that these
   various subtypes can be converted between each other with less loss
   of information then to that of other primary types.  This fact groups
   these subtypes together into the model primary type.  All of the
   expected subtypes have several features in common and that are unique
   to this primary type.

   To loosely summarize: models are multidimensional structures composed
   of one or more objects.  If there are multiple objects then one
   object defines the arrangement/setting/relationship of the others.
   These objects all have calibrated coordinate systems but these
   systems need not be in the same units nor need they have the same
   dimensionality.  In detail:

   1. have 3 or more dimensions which are bases of the system and
      form an orthogonal system (any orthogonal system is sufficient).

      This system is specifically defined in terms of an orthogonal
      set of basis functions [for a subspace of the L^2 function space]
      over a coordinate system of dimension 3 or more. Note that this
      does not preclude regular skewed systems, elliptical coordinates,
      different vector spaces, etc.

   2. contain a structural relationship between model elements.

   3. have scaling or calibration factors which are related to physical
      units (force, momentum, time, velocity, acceleration, size, etc.).
      Thus, an IGES file will specify a building of non-arbitrary size,
      computational meshes and VRML models will have real spatial/



Nelson, et. al.             Standards Track