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Astronomical Data Analysis Software and Systems VII
ASP Conference Series, Vol. 145, 1998
R. Albrecht, R. N. Hook and H. A. Bushouse, e
Ö Copyright 1998 Astronomical Society of the Pacific. All rights reserved.
ds.
Grid OCL : A Graphical Object Connecting Language
I. J. Taylor 1
Department of Physics and Astronomy, University of Wales, College of
Cardi#, PO BOX 913, Cardi#, Wales, UK, Email:
Ian.Taylor@astro.cf.ac.uk
B. F. Schutz 2
Albert Einstein Institute, Max Planck Institute for Gravitational
Physics, Schlaatzweg 1, Potsdam, Germany. Email:
schutz@aei­potsdam.mpg.de
Abstract. In this paper, we present an overview of the Grid OCL
graphical object connecting language. Grid OCL is an extension of Grid,
introduced last year, that allows users to interactively build complex data
processing systems by selecting a set of desired tools and connecting them
together graphically. Algorithms written in this way can now also be run
outside the graphical environment.
1. Introduction
Signal­processing systems are becoming an essential tool within the scientific
community. This is primarily due to the need for constructing large complex
algorithms which would take many hours of work to code using conventional
programming languages. Grid OCL (Object Connecting Language) is a graphi­
cal interactive multi­threaded environment allowing users to construct complex
algorithms by creating an object­oriented block diagram of the analysis required.
2. An Overview
When Grid OCL is run three windows are displayed. A ToolBox window, a Main­
Grid window and a Dustbin window (to discard unwanted units). Figure 1 shows
the ToolBox window which is divided into two sections. The top section shows
the available toolboxes (found by scanning the toolbox paths specified in the
Setup menu) and the bottom shows the selected toolbox's contents. Toolboxes
(and associated tools) can be stored on a local server or distributed throughout
several network servers. Simply adding the local or http address in the toolbox
and tool path setup allows on­the­fly access to other people's tools.
1 A post doctoral programmer at Cardi# who has been developing Grid OCL since January 1996.
2 Professor Schutz is a Director of the Albert Einstein Institute, Potsdam
112

Grid OCL : A Graphical Object Connecting Language 113
Figure 1. Grid OCL's ToolBox window. Toolboxes can be organised
in a similar way to files in a standard file manager.
Units are created by dragging them from the ToolBox window to the desired
position in the MainGrid window and then connected together by dragging from
an output socket on a sending unit to an input socket of the receiving unit. The
algorithm is run by clicking on the start button (see Figure 2), in a single step
fashion (i.e., one step at a time) or continuously.
3. New Features and Extensions
Groups of units can now be saved along with their respective parameters. Such
groups can also contain groups, which can contain other groups and so on. This
is a very powerful feature which allows the programmer to hide the complexity
of programs and use groups as if they were simply units themselves. Many
improvements have been made to the graphical interface, including compacting
the look and style of the toolbox, adding a snap­to cable layout and many more
informative windows. The major change however, is that now Grid consists of
an object connecting language (OCL) and a separate user interface. This means
that the units can be run from within the user interface or as a stand­alone
program.
Collaborators are working on tools for various signal and image problems,
multimedia teaching aids and even to construct a musical composition system.
Currently, in our new release we have toolboxes for various signal processing
procedures, animation and a number of image processing/manipulation routines,
text processing tools e.g., find and replace, grep and line counting recursively
through subdirectories, mathematical and statistical units, a general purpose
mathematical calculator (see next section) and a number of flexible importing
and exporting units.

114 Taylor and Schutz
Figure 2. A snapshot of Grid OCL's programming window.
4. MathCalc
The MathCalc unit interprets, optimises and evaluates arithmetic expressions
using stream­oriented arithmetic. It recognises a large number of functions and
constants. It can be used to evaluate scalar expressions, to process input data
sets, or to generate output data sets. All calculations are performed in double­
precision real arithmetic.
Stream­oriented arithmetic can be defined as the application of an arith­
metic expression to each element of a stream independently. Thus, if B is
the sequence b1, b2, .., bn, then the function sin(B) evaluates to the sequence
sin(b1), sin(b2), ..., sin(bn). MathCalc distinguishes between constants and se­
quences or sets. Sets (data sets) are sequences of numbers and constants are
single numbers, essentially sequences of length 1. In a MathCalc expression the
two can be mixed very freely, with the restriction that all sequences must have
the same length. Sequences or constants can be obtained from the input nodes of
the MathCalc unit. The example given in the MainGrid window (see Figure 2)
demonstrates the flexibility of the MathCalc unit.
The first MathCalc unit creates a 125 Hz sine wave by using the equation
sin(((sequence(512) # 2) # PI) # 0.125) where the sample rate is 1kHz (Math­
Calc will optimise this to (2*PI*0.125) * sequence(512)). This is then trans­
formed into a SampleSet type by adding its sampling frequency (i.e., 1 kHz).
The second MathCalc unit adds Gaussian noise to its input (i.e., by typing
gaussian(512)+#0s). The #0 means node 0 and the s means that it is a se­
quence as opposed to a c which would a constant. The resultant amplitude
spectrum (FFTASpect) is shown from Grapher1 (see Figure 3).
Once the signal is displayed, it can be investigated further by using one of
the Grapher's various zooming facilities. Zooming can be controlled via a zoom
window which allows specific ranges to be set or by simply using the mouse to
drag throughout the image. For example, by holding the control key down and
dragging down the image is zoomed in vertically and by dragging across from
left to right zoomed in horizontally. The reverse operations allow zooming out.
Also once zoomed in, by holding the shift key and the control key down the
mouse can be used to move around the particular area you are interested in. We
also have another powerful zooming function which literally allows the user to
drag to the position of interest and the image will zoom in accordingly.

Grid OCL : A Graphical Object Connecting Language 115
Figure 3. Grapher1's output: any grapher can simultaneously dis­
play many signals each with its own colour and line style.
5. Grid OCL : Past and Present
Grid originated from an implementation of the system using C++ and Inter­
Views (Taylor & Schutz 1995) but was abandoned in early 1996. Version two
(Taylor & Schutz 1996) was written using the Java Development Kit, JDK 1.0.2
but this was updated in order to be compatible with the new JDK 1.1.x kit.
We also re­implemented the base classes and to create OCL. The most recent
version of Grid OCL (in November 1997) is a late alpha and goes by a di#erent
name (Triana OCL 4 ). Triana OCL will be entering its beta testing stage early
next year followed by a final version shortly after. We are in the process of being
able to provide a commercial version of the software for which support can be
given. None­the­less we will always provide it in a free downloadable from the
WWW with a certain time limit (3 or 4 months). Our main goal is to create a
very wide user base.
References
Taylor, I. J. & Schutz, B. F. 1995, The Grid Musical­Signal Processing System,
International Computer Music Conference, 371
Taylor, I. J. & Schutz, B. F. 1996, The Grid Signal Processing System. in ASP
Conf. Ser., Vol. 125, Astronomical Data Analysis Software and Systems
VI, ed. Gareth Hunt & H. E. Payne (San Francisco: ASP), 18
4 http://www.astro.cf.ac.uk/Triana/