Network Working Group                                    S. D. Nelson
Internet Draft                 Lawrence Livermore National Laboratory
                                            Livermore, CA 94550, USA.
                                                             C. Parks
                       National Institute of Standards and Technology
                                         Gaithersburg, MD 20899, USA.
                                    1056 Noe, San Francisco, CA 94114
                                                        February 1996
                                                Expires in six months

                   The Model Primary Content Type for
                  Multipurpose Internet Mail Extensions

Status of this Memo

   This document specifies an Internet standards track protocol for
   the Internet community, and requests discussion and suggestions
   for improvements.  Please refer to the current edition of the
   "Internet Official Protocol Standards" (STD 1) for the
   standardization state and status of this protocol.  Distribution
   of this memo is unlimited.

   The original version of this draft benefitted from discussions
   between the authors and their respective communities.

   Draft documents are 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 draft documents as reference material
   or to cite them other than as ``work in progress.''

   To learn the current status of any Internet-Draft, please check
   the ``1id-abstracts.txt'' listing contained in the Internet-Drafts
   Shadow Directories on (US East Coast), (Europe), (US West Coast), or (Pacific Rim).


        The purpose of this Internet Draft is to propose an update to
   Internet RFC 1521 to include a new primary content-type to be
   known as "model". RFC 1521[1] describes mechanisms for specifying
   and describing the format of Internet Message Bodies via
   content-type/subtype pairs. We believe that "model" defines a
   fundamental type of content with unique presentational, hardware,
   and processing aspects.  Various subtypes of this primary type are
   immediately anticipated but will be covered under separate

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Table of Contents:

   1. Overview
   2. Definition
   3. Consultation Mechanisms
   4. Encoding and Transport
   5. Security Considerations Section
   6. Authors' Addresses
   7. Expected subtypes
   8. Appendix
   9. Acknowledgements

1. Overview

   This document will outline what a model is, show examples of models,
   and discuss the benifits of grouping models together.  This document
   will not directly deal with the intended subtypes since those will be
   covered by their seperate 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 1521.
   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

   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:

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

      The basis functions need to form an orthogonal system, but the
      coordinate system need not be orthogonal.  This also allows for
      regular skewed systems, elliptical coordinates, different vector
      spaces, etc.

   2. contains a structural relationship between model elements.

   3. have calibration factors 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/ temporal units.
      This allows for differing elements to be combined

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   4. Models can also be single descriptive objects or composed of a
      collection of objects.  These normally independent objects are
      arranged in a master/slave scenario so that one object acts as
      the reference which defines how the other objects interrelate
      and behave.  This allows for the creation of mathematical,
      physical, economic, behaviorial, etc. models which typically are
      composed of different elements.  The key is in the description:
      these types describe how something ``behaves''; contrasted to
      typical data types which describe how something ``is''.

      The inclusion of this "collective" system works similar to the
      Email system's multipart/related type which defines the actions
      of the individual parts.  Further specification of the model/*
      subtypes utilizing these properties is left to the subtype

   With these assumptions:

   a. the default dimensionality will be spatial and temporal (but
      any are allowed).

   b. it is presumed that models will contain underlying structure
      which may or may not be immediately available to the
      user. (fluid dynamics vector fields, electromagnetic
      propagation, interrelated IGES dimensional specifiers, VRML
      materials and operators, etc.)

   c. it is assumed that basis set conversion between model domains
      is lossless.  The interpretation of the data may change but
      the specification will not.  i.e. convert the model of the
      U.S.A.  Gross Domestic Product into a VRML model and navigate
      it to explore the variances and interrelationships.  The model
      has many dimensions but also ``passages'' and ``corridors''
      linking different parts of it.  A similar situation is true
      for meshes and CAD files. The key is identifying the basis set
      conversion which makes sense.

   d. models are grouped to assure LESS loss of information between
      the model subtypes than to subtypes of other primary
      types. (i.e.  converting a chemical model into an image is
      more lossy than concerting it into a VRML model).

   Items c and d above define the grouping for model similar to the
   way that ``images'' and ``videos'' are grouped together; to
   assure less loss of information.  Obviously converting from a GIF
   image to a JPEG image looses less information than converting from
   a GIF image to an AU audio file.

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3.  Consultation Mechanisms.

   Before proposing a subtype for the model/* primary type, it is
   suggested that the subtype author examine the definition (above)
   of what a model/* is and the listing (below) of what a model/* is
   not.  Additional consultations with the authors of the existing
   model/* subtypes is also suggested.

   Copies of Internet drafts and RFCs are available on:

   Similarly, the VRML discussion list has been archived as:

   and discussions on the comp.mail.mime group may be of interest.
   Discussion digests for the existing model/* subtypes may be
   referenced in the respective documents.

   The mesh community presently has numerous different mesh
   geometries as part of different packages.  Freely available
   libraries need to be advertised more than they have been in the
   past to spur the development of interoperable packages.  It is
   hoped that by following the example of the VRML community and
   creating a freely available comprehensive library of input/output
   functions for meshes[11] that this problem will be alleviated for
   the mesh community.  A freely available mesh viewer conforming to
   these standards is available now for various platforms.
   Consulations with the authors of the mesh system,

   will be benificial.

   The IGES community has a suite of tests and conformance utilities
   to gauge the conformance to specifications and software authors
   are encouraged to seek those out from NIST[14].

4. Encoding and Transport

   a. A parameter which makes sense for all subtypes of model is the
      initial viewing condition, consisting of the view position (a
      3D point), the view vector, and the up vector.  This parameter
      is optional.  Some subtypes will contain one or more viewing
      conditions as part of there internal data.  If present, this
      parameter over-rides any internal viewing condition.  Note
      that these parameters are not specific to visualizations on
      computer screens but also the default fabrication orientation
      on milling machines.

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   b. Unrecognized subtypes of model should at a minimum be treated
      as "application/octet-stream".  Implementations may optionally
      elect to pass subtypes of model that they do not specifically
      recognize to a robust general-purpose model viewing
      application, if such an application is available.

   c. Different subtypes of model may be encoded as textual
      representations or as binary data.  Unless noted in the
      subtype registration, subtypes of model should be assumed to
      contain binary data, implying a content encoding of base64 for
      email and binary transfer for ftp and http.

   d. The formal syntax for the subtypes of the model primary type
      should look like this:

         MIME type name:          model
         MIME subtype name:       xxxxxxxx
         Required parameters:     none
         Optional parameters:     dimensionality, static/dynamic, def. view
         Encoding considerations: may be encoded
         Security considerations: see section 5 below
         Published specification: see Appendix B for references
         Person and email address to contact for further information:
                                  S. D. Nelson <>

5.  Security Considerations Section

   Note that the data files are ``read-only'' and do not contain file
   system modifiers or batch/macro commands.  The transported data is
   not self-modifying but may contain interrelationships.  The data
   files may however contain a ``default view'' which is added by the
   author at file creation time.  This ``default view'' may
   manipulate viewer variables, default look angle, lighting,
   visualization options, etc.  This visualization may also involve
   the computation of variables or values for display based on the
   given raw data.  For motorized equipment, this may change the
   position from the hardware's rest state to the object's starting

   The internal structure of the data files may direct agents to
   access additional data from the network (i.e. inclusions); the
   security limits of whom are not pre-supposed.  Actions based on
   these inclusions are left to the security definitions of the
   inclusions.  Further comments about the security considerations
   for the subtypes will be contained in each subtype's registration.

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6. Authors' Addresses.

   S. D. Nelson, Lawrence Livermore National Laboratory,
   7000 East Ave., L-153, Livermore CA 94550, USA.

   C. Parks, National Institute of Standards & Technology
   Bldg 220, Room B-344, Gaithersburg, MD 20899, USA.

   Mitra, WorldMaker,
   1056 Noe, San Francisco, CA 94114

7. Expected subtypes

   Table 1 lists some of the expected model sub-type names.  Suggested
   3 letter extensions are also provided for DOS compatibility but their
   need is hopefully diminished by the use of more robust operating
   systems on PC platforms.  The ``silo'' extension is provided for
   backwards compatibility.  Mesh has an extensive list of hints since the
   present variability is so great.  In the future, the need for
   these hints will diminish since the files are self describing.
   This document is not registering these subtypes.  They will be
   handled under separate documents.

   Table 1.

   Primary/sub-type           Suggested extension(s)    Reference

   model/iges                         igs,iges              [8]
   model/vrml                         wrl                   [9]
   model/mesh                         msh, mesh, silo       [10]

   It is expected that model/mesh will also make use of a number
   of parameters which will help the end user determine the data
   type without examinine the data.  However, note that mesh files
   are self-describing.

      regular+static, unstructed+static, unstructured+dynamic,
      conformal+static, conformal+dynamic, isoparametric+static,

   The sub-types listed above are some of the anticipated types that are
   already in use.  Notice that the IGES type is already registered
   as "application/iges" and that RFC states that a more appropriate
   type is desired.  Note that the author of "application/iges" is
   one of the authors of this "model" submission and application/iges
   will be re-registered as model/iges at the appropriate time.

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   The VRML type is gaining wide acceptance and has numerous parallel
   development efforts for different platforms.  These efforts are
   fueled by the release of the QvLib library for reading VRML files;
   without which the VRML effort would be less further along.  This
   has allowed for a consistent data type and has by defacto
   established a set of standards. Further VRML efforts include
   interfaces to other kinds of hardware (beyond just visual
   displays) and it is proposed by those involved in the VRML effort
   to encompass more of the five senses.  Unlike other kinds of
   "reality modeling" schemes, VRML is not proprietary to any one
   vendor and should experience similar growth as do other open

   The mesh type is an offshoot of existing computational meshing
   efforts and, like VRML, builds on a freely available library set.
   Also like VRML, there are other proprietary meshing systems but
   there are converters which will convert from those closed systems
   to the mesh type.  Meshes in general have an association feature
   so that the connectivity between nodes is maintained.  It should be
   noted that most modern meshes are derived from CAD solids files.

8. Appendices

8.1 Appendix A -- extraneous details about expected subtypes

 VRML Data Types

   The 3D modeling and CAD communities use a number of file
   formats to represent 3D models, these formats are widely used
   to exchange information, and full, or lossy, converters
   between the formats exist both independently and integrated
   into widely used applications. The VRML format is rapidly
   becoming a standard for the display of 3D information on the

 Mesh Data Types

   For many decades, finite element and finite difference time domain
   codes have generated mesh structures which attempt to use the
   physical geometry of the structures in connection with various
   physics packages to generate real world simulations of events
   including electromagnetic wave propagation, fluid dynamics, motor
   design, etc.  The resulting output data is then post processed to
   examine the results in a variety of forms.  This proposed mesh
   subtype will include both geometry and scalar/vector/tensor
   results data.  An important point to note is that many modern
   meshes are generated from solids constructed using CAD packages.

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   Motivation for mesh grew out of discussions with other
   communities about their design requirements.  Many CAD or scene
   descriptions are composed of a small number of complex objects
   while computational meshes are composed of large numbers of
   simple objects.  A 1,000,000 element 3D mesh is small.  A
   100,000,000 element 3D structured mesh is large.  Each object can
   also have an arbitrary amount of associated data and the mesh
   connectivity information is important in optimizing usage of the
   mesh.  Also, the mesh itself is usually uninteresting but
   postprocessing packages may act on the underlying data or a
   computational engine may process the data as input.

   Meshes differ principally from other kinds of scenes in that
   meshes are composed of a large number of simple objects which may
   contain arbitrary non-spatial parameters, not all of whom need be
   visible, and who have an implicit connectivity and neighbor list.
   This latter point is the key feature of a mesh. It should be
   noted that most meshes are generated from CAD files however.  The
   mesh type has association functions because the underlying
   physics was used to calculate the interaction (if you crash a car
   into a telephone pole, you get a crumpled car and a bent pole).
   Most interesting computational meshes are 4D with additional
   multidimensional results components.

 IGES CAD Data Types

   (The following text, reproduced for reference purposes only, is from
   ``U.S. Product Data Association and IGES/PDES Organization Reference
   Manual,'' June 1995; by permission.)

   IGES, the Initial Graphics Exchange Specification, defines a
   neutral data format that allows for the digital exchange of
   information among computer-aided design (CAD) systems.

   CAD systems are in use today in increasing numbers for
   applications in all phases of the design, analysis, and
   manufacture and testing of products. Since the designer may use
   one supplier's system while the contractor and subcontractor may
   use other systems, there is a need to be able to exchange data
   digitally among all CAD systems.

   The databases of CAD systems from different vendors often
   represent the same CAD constructs differently. A circular arc on
   one system may be defined by a center point, its starting point
   and end point, while on another it is defined by its center, its
   diameter starting and ending angle. IGES enables the exchange of
   such data by providing, in the public domain, a neutral definition
   and format for the exchange of such data.

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   Using IGES, the user can exchange product data models in the form
   of wireframe, surface, or solid representations as well as surface
   representations. Translators convert a vendor's proprietary
   internal database format into the neutral IGES format and from the
   IGES format into another vendor's internal database. The
   translators, called pre- and post-processors, are usually
   available from vendors as part of their product lines.

   Applications supported by IGES include traditional engineering
   drawings as well as models for analysis and/or various
   manufacturing functions. In addition to the general specification,
   IGES also includes application protocols in which the standard is
   interpreted to meet discipline specific requirements.

   IGES technology assumes that a person is available on the
   receiving end to interpret the meaning of the product model
   data. For instance, a person is needed to determine how many holes
   are in the part because the hole itself is not defined. It is
   represented in IGES by its component geometry and therefore, is
   indistinguishable from the circular edges of a rod.

   The IGES format has been registered with the Internet Assigned
   Numbers Authority (IANA) as a Multipurpose Internet Mail Extension
   (MIME) type "application/iges". The use of the message
   type/subtype in Internet messages facilitates the uniform
   recognition of an IGES file for routing to a viewer or translator.

   Version 1.0 of the specification was adopted as an American
   National Standards (ANS Y14.26M-1981) in November of
   1981. Versions 3.0 and 4.0 of the specification have subsequently
   been approved by ANSI. The current version of IGES 5.2 was
   approved by ANSI under the new guidelines of the U.S. Product Data
   Association. Under these guidelines, the IGES/PDES Organization
   (IPO) became the accredited standards body for product data
   exchange standards. This latest standard is USPRO/IPO-100-1993.

8.2 Appendix B -- References and Citations

   [1] N. Borenstein, and N. Freed, "MIME (Multipurpose Internet Mail
   Extensions) Part One: Mechanisms for Specifying and Describing the
   Format of Internet Message Bodies", RFC 1521, Bellcore, Innosoft,
   September 1993.

   [2] Fitzgerald P., "Molecules-R-Us Interface to the Brookhaven
   Data Base", Computational Molecular Biology Section, National
   Institutes of Health, USA; see for
   further details; Peitsch M.C, Wells T.N.C., Stampf D.R., Sussman
   S. J., "The Swiss-3D Image Collection And PDP-Browser On The
   Worldwide Web", Trends In Biochemical Sciences, 1995, 20, 82.

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   [3] "Proceedings of the First Electronic Computational Chemistry
   Conference", Eds. Bachrach, S. M., Boyd D. B., Gray S. K, Hase W.,
   Rzepa H.S, ARInternet: Landover, Nov. 7- Dec. 2, 1994, in press;
   Bachrach S. M, J. Chem. Inf. Comp. Sci., 1995, in press.

   [4] Richardson D.C., and Richardson J.S., Protein Science, 1992,
   1, 3; D. C. Richardson D. C., and Richardson J.S., Trends in
   Biochem.  Sci.,1994, 19, 135.

   [5] Rzepa H. S., Whitaker B. J., and Winter M. J., "Chemical
   Applications of the World-Wide-Web", J. Chem. Soc., Chem. Commun.,
   1994, 1907; Casher O., Chandramohan G., Hargreaves M., Murray-Rust
   P., Sayle R., Rzepa H.S., and Whitaker B. J., "Hyperactive
   Molecules and the World-Wide-Web Information System",
   J. Chem. Soc., Perkin Trans 2, 1995, 7; Baggott J., "Biochemistry
   On The Web", Chemical & Engineering News, 1995, 73, 36; Schwartz
   A.T, Bunce D.M, Silberman R.G, Stanitski C.L, Stratton W.J, Zipp
   A.P, "Chemistry In Context - Weaving The Web", Journal Of Chemical
   Education, 1994, 71, 1041.

   [6] Rzepa H.S., "WWW94 Chemistry Workshop", Computer Networks and
   ISDN Systems, 1994, 27, 317 and 328.

   [7] S.D. Nelson, "Email MIME test page", Lawrence Livermore
   National Laboratory, 1994. See and

   [8] C. Parks, "Registration of new Media Type application/iges",
   application/iges, 1995.

   [9] G. Bell, A. Parisi, M. Pesce, "The Virtual Reality Modeling
   Language",, 1995.

   [10] S.D. Nelson, "Registration of new Media Type model/mesh",
   (will be)
   mesh, 1995.

   [11] "SILO User's Guide", Lawrence Livermore National Laboratory,
   University of California, UCRL-MA-118751, March 7, 1995,

   [12] E. Brugger, "Mesh-TV: a graphical analysis tool", Lawrence
   Livermore National Laboratory, University of California,

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   [13] S. Brown, "Portable Application Code Toolkit (PACT)", the
   printed documentation is accessible from the PACT Home Page

   [14] L. Rosenthal, ``Initial Graphics Exchange Specification
   (IGES) Test Service'',

8.3 Appendix C -- hardware

   Numerous kinds of hardware already exist which can process some
   of the expected model data types and are listed here for illustration
   purposes only:

      stereo glasses, 3D lithography machines, automated manufacturing
      systems, data gloves (with feedback), milling machines,
      aromascopes, treadmills.

8.4 Appendix D -- Examples

   This section contains a collection of various pointers to
   examples of what the model type encompasses:

   Example mesh model objects can be found on this mesh page:

   Various IGES compliant test objects:

   VRML Test Suite:

   An image of a model of a shipping cage crashing into the ground:

   An image of a 100,000,000 zone mesh:

   A video of a seismic wave propagation through a computational mesh:

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9. Acknowledgements

   Thanks go to Henry Rzepa (, Peter Murray-Rust
   (, Benjamin Whitaker
   (, Bill Ross
   (ross@cgl.ucsf.EDU), and others in the chemical community on which
   the initial draft of this document is based.  That document
   updated IETF Internet Draft, draft-rzepa-chemical-mime-type-01.txt
   in which the initial chemical submission was made, incorporated
   suggestions received during the subsequent discussion period, and
   indicated scientific support for and uptake of a higher level
   document incorporating physical sciences[2-7].  This Model
   submission benefited greatly from the previous groundwork laid, and
   the continued interest by, those communities.

   The authors would additionally like to thank Keith Moore
   (, lilley (, Wilson Ross
   (ross@cgl.ucsf.EDU), hansen (, Alfred
   Gilman (, and Jan Hardenbergh
   ( without which this document would not have been
   possible.  Additional thanks go to Mark Crispin
   (MRC@CAC.Washington.EDU) for his comments on the previous version and
   Cynthia Clark (cclark@CNRI.Reston.VA.US) for editing the submitted

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