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CGM Open specification - WebCGM 2.0 - Introduction to WebCGM


Contents

1. Introduction to WebCGM

This section and its subsections are informative (non-normative).

1.1 About WebCGM

The scope of this WebCGMTM 2.0 specification includes three 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 viewers;
  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.

WebCGM is a set of specifications targeted especially at the effective application of the ISO 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 forms the basis for the WebCGM 2.0 intelligent graphics profile of this WebCGM 2.0 specification.

1.2 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.

1.3 WebCGM requirements

The content of the original WebCGM 1.0 profile was chosen to satisfy the requirements articulated in the document "W3C Scalable Graphics Requirements", http://www.w3.org/Graphics/ScalableReq ([grfreq]), and the specifications and requirements defined in "Use of CGM as a Scalable Graphics Format", http://www.w3.org/TR/NOTE-cgm ([cgmreq]). The content of the WebCGM 1.0 profile was also significantly influenced by technical recommendations from the CGM Open Consortium (see http://www.cgmopen.org/).

The selection criteria for the WebCGM profile include:

The upgraded content of the WebCGM 2.0 profile -- a set of additions, deletions, and modifications applied to the 1.0 profile -- has been shaped by:

The DOM and XCF components of WebCGM 2.0 derive from requirements generated during 5 years of deployment of WebCGM 1.0 in industry. The WebCGM 2.0 Requirements document summarizes these requirements.

1.4 WebCGM and other profiles

The WebCGM 2.0 intelligent graphics profile, like its predecessor 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 represents a major effort towards convergence of intelligent graphics profiles in closely related industries. In fact, it is the intention of the authors and publishers of WebCGM 2.0 that it be used as a basis for the definition of industry-specific profiles. The use of WebCGM as a core profile from which specific-industry technical profiles are derived and defined is defined in Cascading Profiles.

1.5 Editions and releases of WebCGM

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.

This release of WebCGM is Edition 2.0 ("ProfileEd:2.0"). Higher editions may be defined in the future.

This release is the first release of WebCGM 2.0. There may be future releases of WebCGM 2.0, for maintenance and defect correction.

1.6 Roadmap to this specification

WebCGM is written in these major sections:


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