gViz – A Reference Model and
Application of XML for
Visualization on the Grid
Oxford
BROOKES
University
David Duce (daduce@brookes.ac.uk) and Musbah Sagar (msagar@brookes.ac.uk)
This poster explores the potential of XML for visualization in Grid computing. A model for Grid-enabled distributed collaborative visualization
and an XML language to describe a visualization application are presented.
Physical: entities are bound to physical
Introduction
resources
Visualization is a key component for
understanding large-scale simulations and
observations. The gViz project studies
visualization middleware for e-science in a Grid
context. We use IRIS Explorer from NAG Ltd to
carry out some of the implementations needed in
the project.
skML
(Grid Laboratory Open Environment) and
an experimental constraint language (we
call it specML) to express
requirements/constraints on resources.
skML is an XML application (language)
that we use in the gViz project to capture
modules, connections, parameters, etc.
SkML is collaboration-enabled language,
whereby a collection of maps could be
expressed in skML code. Modules within
any map could be connected to or from
any other modules in other maps (see
Figure 4).
Figure 5: Use of GLUE and specML
At the time of writing an IRIS Explorer
collaborative module has been written that
will allow users to collabrate using skML
documents. Users can select a map from
the list of maps available and the module
will take the necessary steps to connect the
cross-linked maps together for the
collaborative session to start.
Figure 1: IRIS Explorer
Haber and McNabb presented the reference
model of modular visualization systems (see
Figure 2 ).
BROOKES
Data
Filter
Map
Render
Figure 2: Haber and McNabb Reference Model
Special attention is paid to Collaboration in the
gViz project since it is key for some modern escience research. The combination of
collaboration and distributed visualization is
known as distributed collaborative visualization
(DCV). DCV calls for collaboration on system
level to enable collaboration at the human level.
The 3-Tier Model
gViz project has a three layered module of
distributed collaborative visualization (see Figure
3).
SVG Map Editor
Figure 4: skML collaborative maps
Multiple maps can be thought of as roles
at the conceptual level (3-Tier layer).
Users may select appropriate map for their
roles.
The following example shows the basic
components of a map in skML language
(modules, links and param) :
<?xml version="1.0"?>
<skml> <map>
<link>
<module name="ReadLat" style="left:20;top:170" out-port="Output">
<param name="Filename">testVol.lat </param>
</module>
<module id="iso" name="IsosurfaceLat"style="left:220;top:120"
In-port="Input">
<param name="Threshold" min="0" max="27">1.8</param>
</module>
</link>
<link>
<module ref="iso" out-port="Surface" />
<module name="Render" style="…" in-port="Input" />
</link> </map> </skml>
Constraints on resources may be
described and associated with skML
module and link elements using RDF
(Resource Description Framework). Here
is an example:
<rdf:RDF
xmlns:rdf="http://www.w3.org/ 1999/02/22-rdfsyntax-ns#"
xmlns:v="http://www.gviz.org/skML/">
<rdf:Description about="RImg">
<v:Type>IrisExplorer</v:Type >
<v:PhysicalLocation rdf:resource=”http:// www.gviz.org/Mars101” />
</rdf:Description>
</rdf:RDF>
Figure 3: 3-Tier Model
Conceptual: visualization to be performed,
independent of software with which to be
realised
Logical: expressed in terms of configuration of
particular entities, independent of physical
resources
Based on pervious work on Javascript and
SVG, an SVG visualization network editor
was developed as a web application. The
editor enables network diagrams to be
constructed in an abstract manner(Figure 6).
Also RDF is used to link resource
requirements (e.g. need 5 processors with
certain characteristics) to maps, modules
or links.
For prove-of-concept we are using a
resource description vocabulary from
GLUE
Figure 6: SVG Map Editor
The editor has a user interface close to the
IRIS Explorer Map Editor (Figure 1). Users
can define new modules, new types of links
and new module libraries. The application
reads/generates skML code. Modules are
coloured based on the map they belong to.
The output skML is generic and can be
translated into any specific visualization
system. RDF, GLUE and specML are to be
used in the near future to annotate modules
and links in a skML visualization map.
Acknowledgements: Discussions with
other partners in the gViz project: the
Universities of Leeds and Oxford, IBM UK
Ltd, NAG Ltd, Rutherford Appleton
Laboratory and Streamline Computing Ltd
are gratefully acknowledged, as is
financial support from EPSRC.