Copyright©2000 CGM Open Consortium, Inc. All Rights Reserved.
What is it?
BHO IS NOT A CGM VIEWER! (If you need a CGM viewer, please have a look at our members' websites.)
CGM Open has developed a Browser Helper Object (BHO) that allows software vendors to build WebCGM viewers that can handle object-level WebCGM addressing when running inside Microsoft Internet Explorer.
Who needs this?
WebCGM product suppliers. Only software developers who want to develop a WebCGM viewer need this BHO, to be able to provide full support for WebCGM addressing.
Who does not need it?
End users. The BHO must not be installed directly on a computer. This will be handled by the installers that install the WebCGM viewer.
Why is the BHO needed?
W3C standards prescribe an extension associated with URLs - the "URL fragment" - which enables specifications such as WebCGM (and SVG) to address individual graphical objects within Web documents or pages. It was discovered that Microsoft Internet Explorer (IE, 5.0 and 5.5 at least) did not correctly handle URL fragments in all necessary situations. The WebCGM BHO solves the problem for WebCGM applications running with IE.
What exactly is a URL fragment?
An example is http://www.cgmopen.org/sample.cgm#myObj. This URL points to the graphical object "myObj" inside the file "sample.cgm" on the CGM Open server. The fragment is the portion of the URL address that follows the "#" character. It is specific to and should be handled by browser plugins or controls for the associated data type. All major browsers do not handle the fragment after the #-character correctly in all cases. This leads to a situation that either the MIME type was not recognized, or the CGM viewer would not get the full URL including the fragment.
What is the solution?
In collaboration with Microsoft, CGM Open developed a solution that examines all CGM URLs that are processed by Internet Explorer. If it encounters a URL that contains a WebCGM fragment it will store this fragment in a safe place so that the WebCGM viewer will be able to access it. WebCGM viewers will have to check this location to find out whether there was a fragment, and then act accordingly.
What is the long-term solution?
Microsoft will change the behavior of Microsoft Internet Explorer in the future. Once this will happen the BHO will no longer be needed.
Does the BHO work with Netscape Navigator or other browsers?
No. This BHO component works only with Microsoft Internet Explorer (IE) -- it is of no use with other browsers, because it is tailored to fit with IE software interfaces. Initial CGM Open results seemed to indicate that Netscape Navigator (NN) did not have the problem. However, more careful testing indicates that NN does indeed suffer from the "#" fragment bug. CGM Open will try to work with Netscape, as we did with Microsoft, to find an equivalent workaround for NN.
Why all of the restrictions in the BHO licenses?
By the nature of the BHO, serious interference and software problems for WebCGM viewers could result from installation of a WebCGM BHO which differs from the CGM Open standard release. CGM Open's BHO license restrictions are aimed at preventing such scenarios.
Distribution & Ordering
The WebCGM BHO is freely available in object code form, to any builders and distributors of WebCGM viewers, and includes sufficient implementors' documentation. Please read the license agreement and follow the instructions below, if you wish to obtain the BHO.
Source code distribution.
Source code for the WebCGM BHO is available to CGM Open members, under an additional source code license. Qualified recipients should please send an email request to firstname.lastname@example.org.
CGM Open will share the technology of the WebCGM BHO with non-CGM Web graphics applications (such as SVG), under a separate Technology License. The BHO will be shared free of charge with qualified recipients under the following license terms and conditions.
If you wish to obtain the BHO, please send an email request for to email@example.com. Include all of the following in your request:
Product with which BHO will be used
Please include the following sentence in your email request, "I have read the CGM OPEN BHO DISTRIBUTION LICENSE at http://www.cgmopen.org/technical/bho/index.html#distribution, and I accept and agree to abide by its terms."
BHO IS NOT A CGM VIEWER!
(If you need a CGM viewer, please have a look at our members' websites.)