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WebCGM 2.1 — Introduction to WebCGM

1. Introduction to WebCGM

This chapter's sections are informative, unless otherwise indicated.


1.1 Terminology

This section is normative.

The key words words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” are to be interpreted as described in [RFC2119].

1.2 Normative references

This section is normative.

ISO/IEC 8632:1999(E)
Information technology - Computer graphics - Metafile for the storage and transfer of picture description information
- Part 1: Functional description
- Part 3: Binary encoding
- Part 4: Clear text encoding

Available at the ISO page of Publicly Available Standards. CGM:1999 was reaffirmed by ISO, without changes, at its 5-year review in 2004. The WebCGM profile is defined by reference to the ISO standard.

ISO Register
ISO International Register of Graphical Items, the normative repository of registered extensions to ISO CGM. Available at http://jitc.fhu.disa.mil/nitf/graph_reg/graph_reg.html. An informative summary of registered CGM items, including pointers into the normative register, is available at http://www.cgmopen.org/technical/registry/ .
ISO/IEC 8632-1:1999/Cor 1:2006
This corrigendum to CGM:1999 corrects an error in the specification of NURBS knots list in CGM:1999. Available at: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=44114 .
ISO/IEC 8632-1:1999/Cor 2:2007
This corrigendum to CGM:1999 clarifies the permissibility and usage rules of Application Structures in the Text Open State of CGM:1999. Available at: http://www.iso.org/iso/iso_catalogue/catalogue_tc/catalogue_detail.htm?csnumber=50315 .
RFC 3986
Uniform Resource Identifiers (URI): Generic Syntax, Eds. T.Berners-Lee, R.Fielding, L.Masinter, January 2005, available at http://www.ietf.org/rfc/rfc3986.txt .
RFC 3987
Internationalized Resource Identifiers (IRIs), M.Duerst, M. Suignard, January 2005, available at http://www.ietf.org/rfc/rfc3987.txt .
RFC 1951
Deutsch, P., "DEFLATE Compressed Data Format Specification version 1.3", RFC1951, Aladdin Enterprises, May 1996. Available at: http://www.ietf.org/rfc/rfc1951.txt .
RFC 1952
Deutsch, P., "GZIP file format specification version 4.3", RFC1952, Aladdin Enterprises, May 1996, available at: http://www.ietf.org/rfc/rfc1952.txt .
ISO/IEC 10646
ISO (International Organization for Standardization). ISO/IEC 10646-1:2000. Information technology — Universal Multiple-Octet Coded Character Set (UCS) — Part 1: Architecture and Basic Multilingual Plane and ISO/IEC 10646-2:2001. Information technology — Universal Multiple-Octet Coded Character Set (UCS) — Part 2: Supplementary Planes, as, from time to time, amended, replaced by a new edition or expanded by the addition of new parts. [Geneva]: International Organization for Standardization. (See http://www.iso.ch for the latest version.)
ISO/IEC 10646-UTF8
ISO/IEC 10646-1:1993, AM2:1996, Information technology — Universal multiple-octet coded character set (UCS) — Part 1: Architecture and Basic Multilingual Plane AMENDMENT 2: UCS Transformation Format 8 (UTF-8). Available from ISO, see http://www.iso.ch .
Information technology – Digital compression and coding of continuous-tone still images – Requirements and guidelines. ITU-T Recommendation T.81. Available at http://www.w3.org/Graphics/JPEG/itu-t81.pdf. . (ISO/IEC 10918-1 : 1993(E))
Portable Network Graphics (PNG) Specification (Second Edition) - Information technology - Computer Graphics and image processing - Portable Network Graphics (PNG): Functional specification. ISO/IEC 15948:2003(E). W3C Recommendation 10 November 2003, available at http://www.w3.org/TR/2003/REC-PNG-20031110 .
RFC 2119
IETF RFC 2119: Key words for use in RFCs to Indicate Requirement Levels, S. Bradner, March 1997. Available at http://www.ietf.org/rfc/rfc2119.txt .
XML 1.0
Extensible Markup Language (XML) 1.0 (Fifth Edition), Eds. T.Bray, J.Paoli, C.M.Sperberg-McQueen, E.Maler, F.Yergeau, November 2008, available at http://www.w3.org/TR/2008/REC-xml-20081126/.
Namespaces in XML
Namespaces in XML 1.0 (Second Edition), Eds. T.Bray, D.Hollander, A.Layman, R.Tobin, August 2006, available at http://www.w3.org/TR/2006/REC-xml-names-20060816/ .
RFC 2781
IETF (Internet Engineering Task Force). RFC 2781: UTF-16, an encoding of ISO 10646, Eds. P. Hoffman, F. Yergeau., February 2000. (Available at http://www.ietf.org/rfc/rfc2781.txt )
RFC 3629
UTF-8, a transformation format of ISO 10646, IETF RFC 3629, STD 63, Ed. F. Yergeau, November 2003. (See http://www.ietf.org/rfc/rfc3629.txt )
The Unicode Consortium, The Unicode Standard, Version 4, ISBN 0-321-18578-1, as updated from time to time by the publication of new versions. (See http://www.unicode.org/unicode/standard/versions/ for the latest version and additional information on versions of the standard and of the Unicode Character Database).

1.3 Non-normative references

SVG 1.1
Scalable Vector Graphics (SVG) 1.1 Specification, Eds. J.Ferraiolo, J.Fujisawa, D.Jackson, January 2003, available at http://www.w3.org/TR/SVG11/ .
DOM Level 3 Core
Document Object Model (DOM) Level 3 Core Specification, Eds. A.Le Hors, P.Le Hégaret (plus L.Wood, G.Nicol, J.Robie, M.Champion, S.Byrne), April 2004, available at http://www.w3.org/TR/2004/REC-DOM-Level-3-Core-20040407/ .
DOM Level 3 Events
Document Object Model Level 3 Events Specification, Eds. B.Höhrmann, P.Le Hégaret, T.Pixley, April 2006, available at http://www.w3.org/TR/2003/NOTE-DOM-Level-3-Events-20031107/ .
HTML 4.01
HTML 4.01 Specification, Eds. D.Raggett, A.Le Hors, I.Jacobs, December 1999, available at http://www.w3.org/TR/html401/ .
CSS 2.0
Cascading Style Sheets, level 2, CSS2 Specification, Eds, B.Bos, H.Wium Lie, C.Lilley, I.Jacobs, May 1998, available at http://www.w3.org/TR/CSS2/ .
Xpointer Framework
XPointer Framework, Eds. P.Grosso, E.Maler, J.Marsh, N.Walsh, March 2003, available at http://www.w3.org/TR/2003/REC-xptr-framework-20030325/ .
Cascading Profiles
Definition and description of how to write a profile using WebCGM as the starting point, for closely related technical application sectors. At http://www.cgmopen.org/technical/cascading-profiles.html .
WebCGM 2.1 Requirements
The requirements used to define the new functionality for WebCGM 2.1. At http://docs.oasis-open.org/webcgm/v2.1/WebCGM_21_Requirements.html.
WebCGM 2.0 Requirements
The requirements on which the major WebCGM 2.0 release was based. At http://www.cgmopen.org/technical/WebCGM_20_Requirements.html .
SpecGL 1.0
The W3C QA Framework: Specification Guidelines has guided the inclusion of the normative Conformance clause, and other conformance-related details of WebCGM. Eds. K.Dubost, L.Rosenthal, D.Hazaël-Massieux, L.Henderson,August 2005, available at http://www.w3.org/TR/qaframe-spec/ .
The IANA registry item for CGM, Final version of CGM Media Type registration, Alan Francis, 1 November 1995, available at http://www.iana.org/assignments/media-types/image/cgm .
Stylable CGM, D.Cruikshank & L.Henderson, a detailed study of possible relationships between WebCGM and CSS, presented at XML Europe 2003, available at http://www.cgmopen.org/technical/stylable_cgm_submitted_0324.pdf .
Unicode TR15
Unicode Standard Annex #15, Unicode Normalization Forms, Eds. M.Davis, M.Dürst, March 2008, available at http://www.unicode.org/reports/tr15/
Character Model for the World Wide Web 1.0: Normalization, Eds. F.Yergeau, M.Dürst, R.Ishida, A.Phillips, M.Wolf, T.Texin, October 2005, available at http://www.w3.org/TR/charmod-norm/ .
UAAG 1.0
User Agent Accessibility Guidelines 1.0, Eds. Ian Jacobs, Jon Gunderson, Eric Hansen, 17 December 2002, a W3C Recommendation available at
http://www.w3.org/TR/2002/REC-UAAG10-20021217/ .
WCAG 1.0
Web Content Accessibility Guidelines 1.0, Eds. Wendy Chisholm, Gregg Vanderheiden, Ian Jacobs, 5 May 1999, a W3C Recommendation available at http://www.w3.org/TR/1999/WAI-WEBCONTENT-19990505/ .

1.4 About WebCGM

The scope of this WebCGMTM 2.1 specification includes these components.

  1. an intelligent graphics profile of the ISO Computer Graphics Metafile (CGM) standard (ISO/IEC 8632:1999), tailored to the requirements for scalable 2D vector graphics in electronic documents on the World Wide Web;
  2. a WebCGM Document Object Model (DOM), which provides an application programming interface to WebCGM objects in WebCGM-supporting applications;
  3. definition of a standard WebCGM XML Companion File (XCF), which allows applications to externalize some non-graphical metadata from WebCGM instances, yet maintain a tight binding of the metadata to WebCGM objects.
  4. definition of an Application Configurable Items (ACI) file, to improve predictability of interpretation of font specifications, and to precisesly specify some under-specified defaults.

WebCGM is a set of specifications targeted especially at the effective application of the ISO CGM:1999 standard to representation of 2D graphical content within Web documents.

CGM has been an ISO standard since 1987, and CGM has been a registered media type (image/cgm) for the Internet and the World Wide Web since December 1995. WebCGM 1.0, comprising the original intelligent graphics profile of ISO CGM, was first published in 1999, was re-released in 2001 with error corrections, and formed the basis for the significant extensions of the WebCGM 2.0 specification.

For much more information about WebCGM, please see the WebCGM FAQ, as well as other numerous other references and reading materials, on the OASIS CGM Open Web site.

1.5 The WebCGM profile and profile rules

The WebCGM profile is a conforming profile of ISO CGM under the stipulations of CGM:1999 Clause 9, "Profiles and conformance", and it utilizes the Profile Proforma (PPF) of CGM:1999 Annex I.1, Proforma tables, for representation of the element-by-element content details.

The WebCGM profile is an "intelligent graphics" profile, which means that in addition to graphical content based on CGM Versions 1-3, the profile includes non-graphical content based on CGM Version 4, Application Structures. The non-graphical content allows the definition of hierarchies of application objects, as well as the association of metadata, such as link specifications and layer definitions, with the objects.

1.6 WebCGM requirements

The original WebCGM 1.0 profile resulted from a collaboration between the CGM Open Consortium and W3C Graphics Activity. The requirements that determined the content selection for WebCGM 1.0 were derived from:

The selection criteria for the WebCGM profile include:

The requirements of the major WebCGM 2.0 release -- a set of additions, deletions, and modifications applied to the 1.0 profile -- were shaped by:

The content of the WebCGM 2.1 profile comprises less than a dozen items that were arguably within the scope of WebCGM 2.0, but which arose too late in the standardization of the latter. The WebCGM 2.1 Requirements document summarizes these requirements.

1.7 WebCGM and other profiles

The WebCGM 2.1 intelligent graphics profile, like its predecessors WebCGM 2.0 and WebCGM 1.0, is a profile of the ISO CGM:1999 standard, designed for effective application of CGM in technical Web applications. WebCGM is not aimed at or optimized for any particular technical application sector, but is intended to satisfy general requirements shared by different but closely related technical Web applications.

Following five years of deployment and application of WebCGM and other technical profiles (such as Air Transport Association's), some divergence began to appear. WebCGM 2.0 represented a major effort towards convergence of intelligent graphics profiles in closely related industries. In fact, starting with version 2.0, it is the intention of the authors and publishers of WebCGM that it be used as a basis for the definition of industry-specific profiles. Cascading Profiles describes the use of WebCGM as a core profile from which specific industries derive and define their technical profiles.

1.8 Editions and releases

CGM:1999 Clause 9, "Profiles and conformance", prescribes that profiles shall maintain revision control by using a standard "ProfileEd" keyword. Instances of a profile carry this edition information in their identification section. Prior releases of WebCGM include:

This specification is the first release of WebCGM 2.1 ("ProfileEd:2.1"). There may be future releases of WebCGM 2.1, for maintenance and defect correction. There may be future higher editions and versions of WebCGM.

A summary of the substantive differences between WebCGM 2.1 and WebCGM 2.0 may be found in the Appendix, "What's new in WebCGM 2.1".

1.9 Roadmap to this specification

WebCGM is written in these major sections:

Note about CGM examples. In Chapter 5, defining the WebCGM DOM, there are examples that end with text lines, "View this example as HTML-CGM (WebCGM-DOM-enabled browsers only.)" In document formats that support external links (i.e., XHTML), each of these examples links to an XHTML snippet that invokes WebCGM instances. To view them your browser must have a WebCGM viewer plug-in, control, or appropriate equivalent technology. To obtain such a viewer, see for example the (non-exhaustive) CGM products directory on the OASIS/CGM Open Web site.

1.10 Document sources and registration authority

Copies of the ISO standards may be obtained from ISO:

ISO Central Secretariat
International Organization for Standardization (ISO)
ch. de la Voie-Creuse
Case postale 56
CH-1211 Geneva 20

For the purpose of this Recommendation and according to the rules for the designation and operation of registration authorities in the ISO/IEC Directives, the ISO and IEC Councils have designated the following as the registration authority:

Joint Interoperability Test Command
ATTN: JTF NITFS Registration Authority (ISO/IEC 9973)
P.O. Box 12798
Fort Huachuca, AZ 85670-2798

For more information on WebCGM and the CGM:1999 standard itself, the CGM Open Web site has a collection of bibliographic references and short articles:

CGM Open

These additional World Wide Web sites have more information on CGM:

W3C WebCGM Overview

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