What is it
CGM (Computer Graphics Metafile) has been an ISO standard for vector and composite vector/raster picture definition since 1987. CGM has a significant following in technical illustration, interactive electronic documentation, geophysical data visualization, amongst other application areas and is widely used in the fields of automotive engineering, aeronatics, and the defence industry.
WebCGM is a profile for the effective application of CGM in Web electronic documents. WebCGM has been a joint effort of the CGM Open Consortium, in collaboration with W3C staff and supported by the European Commission Esprit project. It represents an important interoperability agreement amongst major users and implementors of CGM, and thereby unifies current diverse approaches to CGM utilization in Web document applications. WebCGM's clear and unambiguous conformance requirements will enhance interoperability of implementations, and it should be possible to leverage existing CGM validation tools, test suites, and the product certification testing services for application to WebCGM .
While WebCGM is a binary file format and is not "stylable", nevertheless WebCGM follows published W3C requirements for a scalable graphics format where such are applicable. The design criteria for the graphical content of WebCGM aimed at a balance between graphical expressive power on the one hand, and simplicity and implementability on the other. A small but powerful set of metadata elements is standardized in WebCGM, to support the functionalities of: hyperlinking and document navigation; picture structuring and layering; and, search and query on WebCGM picture content.
Status
The WebCGM Profile specification was issued as a W3C Recommendation on 21st January, 1999 (press release).
This means it is a mature document that is considered to contribute towards realising the full potential of the Web. Viewers for CGM are available on many platforms and are being adapted to support the WebCGM Profile specification.
MIME type
CGM has been a registered MIME type since 1995. The MIME type for CGM is unusual in that it requires two parameters - the CGM version, and the CGM Profile in use. This is because, without Profiles, it is very difficult to achieve interoperability with CGM (which is why W3C issued a WebCGM Profile). It also means that the MIME type does not need to be re-registered whenever there is a new profile.
Thus the correct MIME type for WebCGM is:
image/cgm;Version=4;ProfileId=WebCGM
More information
There is a white paper on WebCGM on the CGM Open Website
More information will be added, watch this space.
