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Astronomical Data Analysis Software and Systems IV
ASP Conference Series, Vol. 77, 1995
R. A. Shaw, H. E. Payne, and J. J. E. Hayes, eds.
The PROS Big Picture: A High­Level Representation of a
Software System
J. DePonte, J. Chen, K. R. Manning, D. Schmidt, and D. Van Stone
Smithsonian Astrophysical Observatory, 60 Garden St., Cambridge MA
02138
Abstract. We present a high­level representation of the packages and
tasks within IRAF/PROS. The development of this overview is part of a
comprehensive plan to document, and to improve consistency throughout,
the IRAF/PROS analysis software. We anticipate that both current and
future programmers will benefit from this document, and that the guide­
lines we have established will be applicable to other software projects.
1. Introduction
PROS is a multi­mission X­ray analysis software system designed to run under
the Image Reduction and Analysis Facility (IRAF) (Tody 1986). The PROS
software includes spatial, spectral, timing, data I/O, and plotting applications,
and algorithms for performing general arithmetic operations with image data
(Worrall et al. 1992). We have produced a high­level overview of PROS. The
present paper describes this picture and the project that produced it.
2. Approach
A project to document a system requires a good definition for success. It can
easily become unwieldy and misguided. The approach we took was based on four
objectives. The first three were: a statement of mission, or what the project
was intended to accomplish; a strategic plan to meet the objectives; and a set
of short­term goals, to be met by means of scheduled task assignments. We also
defined our long­term goals, a broader context for the mission.
The mission statement for the PROS overview specified four objectives: to
communicate the content and organization of PROS to current and future pro­
grammers and projects; to make it easier to maintain the system and to evaluate
enhancements; to identify code of high algorithmic content, for possible inclu­
sion in libraries; and to identify temporary or prototype code for replacement
or elimination.
The strategy was to do the project in stages, focusing at each stage on
low­effort, high­payoff work that would produce useful deliverables. The incre­
mental stages were the short­term goals: a project overview diagram (i.e., an
organizational diagram of software modules); high­level diagram (i.e., a bubble
diagram of each module in the system); and unifying element tables (i.e., tables
of task vs. software attributes).
1

2
3. Implementation
To meet the long term goals within short term objectives, a hierarchical chart
showing all packages and tasks was developed. The diagram was the basis for
task assignments and progress evaluation (see Figure 1).
Next, we developed a high­level representation of the system. Each task
was shown along with file I/O in a bubble diagram. Connectors were placed
to show paths to other tasks within the same package. Standard analysis and
design diagramming were applied, but standards were customized when appro­
priate for the application. For example, we used our own notation to represent
inclusive/exclusive ORs and defined an icon to represent graphical output (see
Figure 2).
Once diagrams were generated for all of the PROS tasks, the unifying el­
ements of the system were identified. The elements (e.g., file I/O, code/data
dependencies, maintenance of header keywords) were derived by analyzing the
libraries and key software modules. We represented them as table columns and
categorized the elements into four groups: I/O attributes (i.e., activities such
as file I/O for each type of data file in the system); data attributes (e.g., the
dependence of reference data on time); form attributes (e.g., whether the task is
compiled code or a script, or whether it utilizes lookup tables); and derived at­
tributes (e.g., whether the task maintains WCS or file header values, or performs
error computation).
Next, a unifying element table was built for all tasks in the system. In the
table, elements were represented as columns and tasks as rows. The parameter
files, help files, and code, were used to analyze the modules and complete the
tables. Table 1 shows an example of a table of I/O attributes of tasks in the
PROS xtiming package.
The last phase focused on each identified attribute, documenting its usage
in the code. Different projects could use different views for this phase of docu­
menting their systems. For example, the structure charts of each module could
be derived, or one aspect of the larger infrastructure could be identified and ex­
amined. In our preliminary work on this phase, we have taken the latter course,
investigating the interrelations among library routines involved in implementing
regions and masks.
4. Project Status
We have completed the project overview diagram, the bubble diagrams, and the
attribute vs. task tables for all modules in PROS. We are currently analyz­
ing code with identified attributes and documenting the usage throughout the
system.

3
fold period ltcurv fft vartst qpphase
qpoe sregion bregion exp.pl
ltc.tab fft.tab var.tab ig1.tab ig2.tab phase.qp
fld.tab fld.tab chi.tab pwr.tab ftp.tab
bk.qp
sti.qp
timfilter
tab qpoe tab
timplot timcor
timsort
ftpplot
fldplot chiplot ltcplot fftplot ksplot
timprint
stdout stdout
xtiming
Figure 1. Task organization chart for the PROS package.
xrfits
xwfits
upqpoerdf
upimgrdf
rfits2pros
rarc2pros
qpgapmap
qpappend
qpaddaux
qp2fits
mperfits
mkhkscr
hkfilter
fits2qp
efits2qp
datarep
ecd2pros
ecdinfo
eincdpar
eindatademo
imcalc
imcompress
imcreate
imnode
imreplicate
plcreate
pllist
qphedit
qpcopy
qplintran
qplist
qpshift
qprotate
qpsort
xhadd
xhdisp
xdataio ximages
eincdrom
ltcurv
period
fold
fft
vartst
timsort
timfilter
qpphase
chiplot
fftplot
fldplot
ftpplot
ksplot
ltcplot
timprint
timplot
apply_bary
calc_bary
scc_to_utc
xtiming
timcor
xspectral
qpspec
fit
singelfit
xflux
hxflux
search_grid
bal_plot
counts_plot
grid_plot
dofitplot
show_models
upspecrdf
downspecrdf
imcontour
pspc_hrcolor
tabplot
tvimcontour
tvlabel
tvproj
xdisplay
xexamine
ximtool
xplot
. . .
XRAY
intrisicspecplot
Figure 2. Bubble diagram for the PROS xtiming package.

4
Task imio qpio plio tabio ASCII bin FITS stdout plt
ltcurv -- x -- x -- -- -- -- --
period -- x -- x -- -- -- -- --
fold -- x -- x -- -- -- -- --
fft -- x -- x -- -- -- -- --
vartst -- x -- x x -- -- -- --
timfilter -- x -- -- x -- -- x --
timplot -- -- -- x -- -- -- x --
qpphase -- x -- -- -- -- -- -- --
ksplot -- -- -- x x -- -- -- x
Table 1. Data I/O attributes table. The columns are I/O attributes.
The rows are tasks in the xtiming package. Attributes that apply to a
task are marked with an ``x''. Attributes that do not apply are marked
with a ``--''.
5. Conclusion
The implementation decisions enabled us to produce useful products at each
phase of the project. The high­level graphical representation of the system has
already proved a useful tool in communicating PROS to others. The attribute
vs. task tables identify library code, flag code that are trouble spots in preparing
a software release, and aid in evaluating test procedures.
We anticipate that the procedures that we have established will be appli­
cable to other large software projects. The effort we describe distinguishes each
phase and can be customized to bring added understanding to a large software
system.
Acknowledgments. This work is partially supported by NASA contracts
to the ROSAT Science Data Center (NAS5--30934) and Einstein (NAS8--30751).
References
Tody, D. 1986, in Instrumentation in Astronomy VI, Part 2, SPIE, 627
Worrall, D. M., et al. 1992, in Data Analysis in Astronomy IV, eds. V. Di Ges`u,
L. Scarsi, R. Buccheri, P. Crane, M. C. Maccarone, & H. U. Zimmermann
(New York, Plenum Press), p. 145