W3A Questions and Answers
Here are some questions about and objections to W3A. I've added
tentative answers, but the discussion isn't over yet. This
document is meant as a summary of the most important questions and
it will be extended as the discussion continues. (Last updated: 27
June 1994.)
(Terry Allen <terry@ora.com>)
I assumed that stylesheets are explicitly linked to an HTML
document as For general SGML: I don't know... Does anybody know how style
sheets are supposed to be linked to document instances, e.g., in
DSSSL? [BB]
(Daniel W. Connolly <connolly@hal.com>)
Good point. On HP-UX, the easiest implementation is with
shared libraries instead of dynamic loading; can't Windows DLLs
be loaded explicitly? If not, is there a more or less portable
solution at all?
However, when the source of the browser is available for
re-compilation, the same API can also be used for normal
linking. [BB]
(Daniel W. Connolly <connolly@hal.com>)
You can still do that (link the Python interpreter as an
`applet'). Maybe there are better ways. I certainly like the
possibility to quickly hack a new applet in Python, but I
wouldn't like to restrict applets to Python or some other
interpreted language only. [BB]
(Daniel W. Connolly <connolly@hal.com>)
Not quite, there is either a file descriptor or an ID (`magic
cookie') to identify the particular instance of the applet. I
can change (Daniel W. Connolly <connolly@hal.com>)
That can be easily fixed. I regard the preference as the
user's choice, so it is basically a change to the configuration
file (and the (Daniel W. Connolly <connolly@hal.com>)
This is something that I've been thinking about but
that I couldn't solve. I think about it as `synchronization' but
I have difficulty finding a good model for it. Yes, HyTime may
hold a clue here, but adding HyTime to the browser is far from
trivial. [BB]
(Daniel W. Connolly <connolly@hal.com>)
Yes, that is high on my agenda. But I do hope that status
codes in combination with the errno variable are
enough, though. I know it is old-fashioned and it relies on the
programmer being conscientious, but the scheme is traditional,
well understood and easy to implement.
I've worked with the Python model of exception handling (in
another language) and it certainly cleans up the code and it
also ensures that no exception goes unnoticed. So, proposals are
still welcome. [BB]
(Daniel W. Connolly <connolly@hal.com>)
Why do we need applets to be in a bounded runtime environment
(in casu an interpreter)? I need more arguments [BB]
(Daniel W. Connolly <connolly@hal.com>)
In my view, such a script is simply another document that is
downloaded to just another `viewer' applet (`view' in a
generalised sense...), although it brings one back to the
`synchronization' issue (see above). [BB]
No. If the look & feel of a certain applet doesn't suit
you, you'll have to find (or write) another one.
The browser and the applets may be multithreaded, but neither
side may assume that the other can deal with concurrent access.
In other words: all calls to the API functions must occur in the
same thread (maybe this can be relaxed a bit, with careful coding?)
The simplest answer is that the viewer applet for
`message/rfc822' will include an editor and appropriate commands
for this. However, one might want to use a separate editor
accessory if one exists... any ideas?
Sending a message after it has been composed is handled
within W3A with the Some browsers may have this command built in, but it could
also be a function of some viewers.
Again, some browsers may have this command, but it is more
likely that a viewer implements it, since it is supposed to know
more about the format of the data.
A browser could, of course, offer this feature. In that case
it is a user-interface issue. But it is currently not possible
from within a viewer. I can imagine that a viewer wants to
specify particular `Accept:' headers when it processes in-line
images. So, some mechanism must be found for this.
I'll have to think about this. How about a variable-length
argument list for the How do SGML style sheets fit in?
<LINK REL=Style
HREF="layout.sty">. The HTML viewer must call
W3AopenDoc(), W3AreadDoc() and
W3AcloseDoc() in order to get the style sheet.
Dynamic linking is too Unix-specific
Why not use Python (or Scheme48 or...) to write
applets in?
The `objects' in these interfaces (the browser, for example)
are implicit in the function calls, causing the state for the
objects to be stored in global variables
int to void * and call it
`self' instead of `fd'. Would that help? (I like it better as it
is, though.) [BB]
It doesn't allow browsers to `prefer' one format over
another.
W3ABrowserInfo structure, of course.)
[BB]
Can it deal with a hypermedia document architecture that
accomodates compound/complex documents with links between
them?
There is no coherent exception mechanism (i.e. no error
handling model)
We need two kinds of `safe' programming languages: the
lisp/perl/smalltalk/python style safe language where the
programmer can't screw up the runtime system the way one can
with C and C++...(cont'd)
... and the safe-tcl/Obliq/telescript style safe language
where untrusted code can be run with bounded access to
resources.
Can consistency of the GUI be ensured?
Is multithreading possible?
How is posting news, or replying to mail handled?
W3Aopen and
W3Awrite functions, provided the necessary agents
are loaded, of course.
Where is the `View source' command handled?
Where is the `Save to file' command handled?
Can the user dynamically change the `Accept:' headers, e.g.,
to temporarily prefer one format over another?
W3Aopen function, containing
`Accept:' lines?