rfc2077.txt

著名的RFC文档,其中有一些文档是已经翻译成中文的的.

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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.













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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 examine the data.  However, note that mesh files are self-
   describing.

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

   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.

   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 standards.

   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.








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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 WWW.

 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.

   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.



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 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.

   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



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   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] Freed, N., and N. Borenstein, "Multipurpose Internet Mail
   Extensions (MIME) Part One: Format of Internet Message Bodies", RFC
   2045, Innosoft, First Virtual, November 1996.

   [2] Fitzgerald P., "Molecules-R-Us Interface to the Brookhaven Data
   Base", Computational Molecular Biology Section, National Institutes
   of Health, USA; see http://www.nih.gov/htbin/pdb 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.

   [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.





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   [7] S.D. Nelson, "Email MIME test page", Lawrence Livermore National
   Laboratory, 1994. See http://www-dsed.llnl.gov/documents/WWWtest.html
   and http://www-dsed.llnl.gov/documents/tests/email.html

   [8] C. Parks, "Registration of new Media Type application/iges",
   ftp://ftp.isi.edu/in-notes/iana/assignments/media-types/
   application/iges, 1995.

   [9] G. Bell, A. Parisi, M. Pesce, "The Virtual Reality Modeling
   Language",
   http://sdsc.edu/SDSC/Partners/vrml/Archives/vrml10-3.html, 1995.

   [10] S.D. Nelson, "Registration of new Media Type model/mesh",
   ftp://ftp.isi.edu/in-notes/iana/assignments/media-types/model/
   mesh, 1997.

   [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,
   UCRL-TB-115079-8, http://www.llnl.gov/liv_comp/meshtv/mesh.html

   [13] S. Brown, "Portable Application Code Toolkit (PACT)", the
   printed documentation is accessible from the PACT Home Page
   http://www.llnl.gov/def_sci/pact/pact_homepage.html

   [14] L. Rosenthal, "Initial Graphics Exchange Specification
   (IGES) Test Service",
   http://speckle.ncsl.nist.gov/~jacki/igests.htm

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.











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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:
      http://www-dsed.llnl.gov/documents/tests/mesh.html

   Various IGES compliant test objects:
      http://www.eeel.nist.gov/iges/specfigures/index.html

   VRML Test Suite:
      http://www.chaco.com/vrml/test/

   An image of a model of a shipping cage crashing into the ground:
      http://www.llnl.gov/liv_comp/meiko/apps/dyna3d/cagefig2.gif

   An image of a 100,000,000 zone mesh:
      http://www.llnl.gov/liv_comp/meiko/apps/hardin/PMESH.gif

   A video of a seismic wave propagation through a computational mesh:
      http://www.llnl.gov/liv_comp/meiko/apps/larsen/movie.mpg

9. Acknowledgements

   Thanks go to Henry Rzepa ([e-mail]), Peter Murray-Rust
   ([e-mail]), Benjamin Whitaker
   ([e-mail]), Bill Ross ([e-mail]),
   and others in the chemical community on which the initial draft of
   this document is based.  That document updated an IETF Internet Draft
   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
   ([e-mail]), lilley ([e-mail]), Wilson Ross
   ([e-mail]), hansen ([e-mail]), Alfred Gilman
   ([e-mail]), and Jan Hardenbergh ([e-mail])
   without which this document would not have been possible.  Additional
   thanks go to Mark Crispin ([e-mail]) for his comments
   on the previous version and Cynthia Clark ([e-mail]) for
   editing the submitted versions.






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