RFC008

Title: DAS Visualization Server
Author: Alex Rolfe <arolfe@genome.wi.mit.edu>
Dependencies: Directory Services
Version: 1
Date: 20 August 2001

The DAS/1 protocol includes a Stylesheet request which allows
the annotation server to provide hints as to how to display
annotations.  There are two problems:
 1) The annotation server should be concerned only with annotation
 data.  It should not play any role in visualization as this breaks the
 abstraction between the underlying data and the its presentation.
 2) The client is left to do most of the visualization work
 (e.g. scrolling, rendering, deciding which features are visible
 at some).  Some clients might wish to access DAS data without
 implementing a full DAS rendering engine.

A better approach might involve a third type of DAS server strictly for
visualization.  The annotation server would no longer respond to a
Stylesheet request; instead, the visualization server would be
responsible for Stylesheet and other visualization requests. 

The visualization server could provide more complex services such as
static rendering of annotations.  A client would wrap a features request
in a visualization request.  The visualization request could also
specify the desired response format: static image (jpeg, png, etc) or
perhaps and applet that can show the data (e.g. an omniview applet).
The visualization server would retreive the features from an annotation
server of its choosing (probably a local server to ensure reasonable
performance) and return a rendering in the desired format.  The server
could reject any part of the request.  It might refuse to access a
particular data source (i.e. it will only access a local annotation
server) or it might not provide responses in a certain format.

The visualization server could be implemented in the same software as an
annotation server (just as the reference and annotation servers can be
the same software).  In either case, the server would be registered as
being a DAS visualization server in whatever Directory Services
system is used, making it easy for clients to find.