pp g y p y g g g ,
San Diego, California, Decemb er 1995.
VRweb: A Multi-System VRML Viewer
Michael Pichler, Gerb ert Orasche, Keith Andrews
1
I ICM, Graz UniversityofTechnology
Ed Grossman
2
National Center for Sup ercomputing Applications
Mark McCahill
3
University of Minnesota
Abstract form of Silicon Graphics' Inventor [27 ] le format, an ex-
tensive, proven 3D graphics le format which includes a va-
riety of sp ecial-purp ose no des. VRML adopted Inventor's
As VRML b ecomes the standard for describing
no de-based hierarchical structure, eld syntax and instanc-
3D scenes on the Internet, many VRML viewers
ing mechanism, but left out a numb er of its sp ecial-purp ose
are b eing develop ed with proprietary interests or
and more esoteric features. VRML de nes no des for geom-
for sp eci c target systems or proto cols.
etry p olygon based and primitive shap es , text, grouping,
VRweb is a VRML viewer providing the same
multiple levels of detail, transformations elementary and ar-
user interface for multiple Web proto cols WWW,
bitrary matrices , co ordinates, normal data, prop erties ma-
Gopher, and Hyp er-G and multiple platforms
terials, textures , rendering attributes bindings and shap e
Unix, Windows, and Macintosh and is avail-
hints , light sources p ositional, directional, sp ot lights , and
able as b oth binary and source co de. VRweb
camera de nitions p ersp ective and orthographic .
source co de is copyrighted, but is freely avail-
The World Wide Web WWW, W3, or \The Web" [8 ],
able for non-commercial use, providing a plat-
currently the most p opular Internet information system, is
form for research and exp eriment. Unlike other
based on the HTML [9 ] markup language and the HTTP
VRML viewers available in source co de, VRweb
client/server proto col. Navigation is primarily achieved by
do es not require additional commercial libraries
means of hyp erlinks. In contrast, navigation in the Internet
like Op enInventor or Motif, it is based entirely
Gopher [16 ] is primarily hierarchical, including its new 3D
on freely available software comp onents.
interface, GopherVR [17 ]. Both WWW and Gopher supp ort
A short overview of currently available VRML
add-on search facilities. Hyp er-G [4 , 5 ] combines hierarchi-
browsers is followed by a more detailed lo ok at
cal and hyp erlink navigation with fully integrated search fa-
VRweb, including its user interface, multi-system
cilities, whilst remaining interop erable with WWW and Go-
nature, and software architecture.
pher Hyp er-G servers sp eak WWW and Gopher proto cols
as well as native Hyp er-G . All three systems allow VRML
mo dels residing on their resp ective servers to b e accessed by
their supp orted access proto cols.
Keywords: VRML, WWW, Gopher, Hyp er-G, Op enGL,
The Web's URL Universal Resource Lo cator mecha-
X11, Windows, Internet, Web.
nism allows do cuments and les residing on arbitrary servers
somewhere on the Internet to b e sp eci ed using one conve-
1 Intro duction
nient handle: a do cument's URL includes its access pro-
to col for example http, gopher, ftp, or hyp erg . VRML's
The Virtual Reality Mo deling Language [7, 24 ], or VRML
WWWInline and WWWAnchor no des utilise the URL mech-
for short, is evolving as a standard data format for the
anism. The former allows a scene to b e split into parts which
storage and interchange of 3D mo dels in information sys-
may b e fetched on demand, for example when navigating a
tems and mo deling packages. VRML is based on the ascii
large, complex mo del comp onents of the mo del are fetched
1
as one approaches them imp ortantonaslow network con-
Institute for Information Pro cessing and Computer Supp orted
nection . The latter supp orts link anchors attached to ar-
New Media I ICM , Graz Universityof Technology, A-8010 Graz,
Austria. fmpichler,gorasche,[email protected]
bitrary comp onents of a scene; these can b e clicked to load
2
National Center for Sup ercomputing Applications NCSA , Uni-
related VRML or other les. Imp ortant for the backward-
versity of Illinois, Urbana-Champaign. [email protected]
compatibility of extensions to VRML is the p ossibility for a
3
Distributed Computing Services, University of Minnesota.
no de to provide a description of its elds and optionally
mpm@b o ombox.micro.umn.edu
the name of a base no de that can b e used as its substitute.
VRML 1.0 supp orts only static scene descriptions; dynamic
ob ject b ehaviour is now under discussion for inclusion in
VRML 2.0.
2 Related Work
Since the release of the rst VRML viewers/browsers in
April 1995, there have b een a o o d of releases and announce-
ments. Here we presentanoverview of the eld as of Au-
Figure 1: The VRweb VRML viewer displaying Lightscape's model of Jerusalem City Hal l.
i3D [10 ] from the Center for Advanced Studies, Research gust 1995 which is necessarily neither complete nor up-to-
and Development in Sardinia exploits the rendering capabil- date . We use the term browser to refer to software which
ities of high-end machines. This VRML viewer includes a itself retrieves VRML les across the Internet and viewer
prepro cessing optimisation phase and time-dep endent ren- for software which relies on another supp orting application
dering facilities to guarantee constant frame rates even for to p erform le retrievals.
very large scenes. It is available only for SGI machines. WebSpace [26 ] from Silicon Graphics in collab oration
WebOOGL [18 ] from the Geometry Center of the Uni- with Template Graphics was the rst VRML browser to b e
versity of Minnesota is available in source co de based on released. WebSpace is based on the Inventor library and
Geomview. Geomview is a program for viewing and manip- has two navigational metaphors the examiner viewer and
ulating 3D ob jects and is designed to act as display unit for walk viewer . WebSpace binaries are freely available un-
external mo dules creating geometry. Multiple control win- supp orted with a supp orted commercial version; no source
dows exist for motion control, prop erties and editing. The co de is available. WebSpace runs on SGI, IBM AIX, Sun
WebOOGL browser is available for SGI and Sun OS plat- Solaris with graphics b oard , and Windows NT; versions
forms. for Macintosh, DEC and HP are planned.
VRweb , the VRML viewer describ ed in this pap er, is WebView [25 ] from the San Diego Sup ercomputer Center
a joint pro ject between I ICM home of Hyp er-G , NCSA SDSC is a publically available VRML browser for SGI sys-
home of Mosaic , and the University of Minnesota home tems, available as source co de based on the Inventor library.
of Gopher . It draws on several years of exp erience with the WebView has four viewing styles examiner, y, plane, walk
Harmony 3D Scene Viewer [2, 6 ] for Hyp er-G, which b ecame and an integrated editing facility. It can either b e run as a
the base of VRweb. VRweb is designed to work with mul- standalone browser or as an external viewer with a Web
tiple information systems, namely WWW, Hyp er-G, and browser. It is intended as a public development and test
Gopher, as well as on a variety of platforms. It is cur- platform, but is limited to SGI platforms under UNIX.
rently available for most common UNIX platforms SGI WorldView [12 ] from InterVista Software is targeted to
IRIX, Sun Solaris, Sun OS, DEC Alpha, DEC ULTRIX, emp ower standard PCs for real-time applications. All net-
HP-UX, and LINUX as well as Windows NT, 3.1, 95 ; work communication is built into this standalone browser,
a Macintosh version is exp ected by the time this pap er is which do es not rely on a co op erating Web browser. World-
published. VRweb source co de with copyright is available View is available for all Windows platforms NT, 3.1, 95 ;
free of charge for non-commercial use, providing a platform versions for Macintosh and UNIX SGI, Sun OS are planned.
for research and exp eriment. Unlike other VRML viewers WebFX [21 ] from Pap er Software is a VRML browser
available in source co de, VRweb do es not require additional for the Windows environment. The binaries are free for
commercial libraries like Op enInventor or Motif, it is based non-commercial use and during an evaluation p erio d. It in-
entirely on freely available software comp onents see Sec- corp orates IRC3Dchatting and physically-based navigation
tion 5 for more detail ab out VRweb's software architecture . metaphors including collision detection as well as VRML
Figure 1 shows VRweb displaying Lightscap e's [13 ] VRML authoring facilities. It is available for Windows platforms
mo del of the chamb er of Jerusalem City Hall. NT, 3.1, 95 ; a Macintosh version is planned.
Figure 2: VRweb for Windows in Heads-Up navigation mode. Icons are overlaid atop the viewing area for looking, walking,
vertical/sideways motion, and point-of-interest navigation. The rendering mode may be set separately for faster interactive
navigation.
Figure 3: VRweb for Unix in Fly Mode through VirtualSOMA. The speed of ight is overlaid in the bottom right corner of the
viewing area, the direction of ight is determined by the position of the cursor relative to the central target crosshairs.
3 The VRweb User Interface can b e displayed in the status area. The Hyp er-G version
of VRweb also supp orts interactive, p oint-and-click link cre-
The VRweb window is divided vertically into four areas:
ation.
menu bar, to ol bar, display area, and status bar. The menu
Figure 2 shows the VRweb user interface in Heads-Up
bar provides access to the full functionality of VRweb, the
navigation mo de. Figure 3 shows a user is navigating in Fly
to ol bar and additional accelerator keys provide quick access
mo de through VirtualSOMA [23 ], the VRML mo del of the
to commonly used functions.
South of Market area of San Francisco.
VRweb supp orts ve rendering mo des: wire frame, hid-
den line, at shading, smo oth shading, and texturing; the
4 VRweb as a Multi-System VRML Viewer
rendering mo de sp eci ed in the VRML le can b e overrid-
den. A separate rendering mo de may b e sp eci ed for use
VRweb can either b e used b oth as a standalone viewer to
during interactive navigation. For example, on a display
view lo cal VRML les e.g. b efore putting them onto a
without hardware graphics acceleration where frame rates
server or in conjunction with a WWW, Hyp er-G, or Go-
are slow for textured mo dels, it might b e advisable to navi-
pher client to view VRML les on the Net. Dep ending on
gate in wire frame mo de and see a textured version only in
the particular con guration, VRweb either functions as a
the pauses b etween interaction.
passive help er application unable to resolve external URLs
Navigation in 3D space is complicated by the need to
or as a partner application connecting back to the particu-
control at least six degrees of freedom at the same time.
lar browser to resolve URLs as the need arises for exam-
VRweb do es not assume the availabilityofany sp ecial 3D
ple, when a link anchor is clicked . A bidirectional connec-
input device, such as a spaceball or p osition/orientation sen-
tion to the client is necessary to retrieve anchor destina-
sors, and provides a numb er of natural mappings for a stan-
tions WWWAnchor no des and inlined scenes WWWIn-
dard 2D mouse. There are basically two classes of viewp oint
line no des , since VRweb do es not itself sp eak HTTP, Hyp er-
control metaphor, dep ending on whether users wish to move
G, or Gopher proto col. A bidirectional connection is also
the mo del itself or to move themselves through the mo del.
useful for general browsing functionality, such as op ening a
Mo dels of objects are typically moved and examined, mo dels
do cument of arbitrary typ e, going back and forward in the
of scenes are typically navigated through walking, ying,
history, retrieving help les, and setting hotlist entries.
etc. . To cop e with these di erent needs, VRweb provides
venavigation metaphors.
Flip mo de is used to examine an ob ject, whilst the viewer
4.1 VRweb and WWW
remains stationary. The mouse buttons have assignments for
VRweb can use NCSA Mosaic [1 , 19 ] to resolve WWWIn-
translation, rotation, and zo oming the ob ject .
line and WWWAnchor requests. The Common Client In-
The Walk metaphor is used to stroll through a 3D envi-
terface CCI allows external applications such as VRweb
ronment. Natural walking motion forwards and backwards,
to communicate with running sessions of NCSA Mosaic via
p ossibly veering slightly to left or right is assigned to the
TCP/IP or OLE . VRweb uses Mosaic to resolve requests
left mouse button. Complementary controls for vertical mo-
for VRML scenes from an http d server, and to manage the
tion and side-stepping, and for turning the head are assigned
display of non-VRML do cuments which might b e referenced
to the middle and right mouse buttons resp ectively.
in a WWWAnchor no de.
Fly is like piloting an aircraft. Flight direction is con-
When VRweb is invoked generally as a help er applica-
trolled by the p osition of the mouse cursor relative to the
tion, with a temp orary le containing the scene le as a
mid-p oint of the viewing window denoted by a cross-hair .
parameter it makes a CCI connection to Mosaic, and re-
The left mouse button activates ight, the other two mouse
quests that all do cuments with the VRML MIME typ e b e
buttons control acceleration and deceleration. The current
sent directly to it. It also asks Mosaic to notify it any time
direction and sp eed are indicated in an overlay atop the dis-
a new anchor is activated. Finally, it asks Mosaic to giveit
play area.
the URL corresp onding to the le name with whichitwas
Fly To mo de implements p oint-of-interest POI style
invoked, which is displayed to the user in the status box,
navigation [15 ]. Here, the user rst selects a p oint of in-
and displays the scene.
terest somewhere in the mo del and is then able to p erform
Subsequent scenes are passed directly to VRweb through
controlled, logarithmic motion towards and away from the
the CCI so cket. Because VRweb is noti ed whenever an
POI, approaching by the same fractional distance in each
anchor is activated via Mosaic, it can determine any scene's
time step. Optionally, a rotational comp onent can b e acti-
corresp onding URL and, dep ending on howitwas requested,
vated with the Shift key , which results in a nal approach
display it as either an inline no de or an entirely new scene.
path to the POI head-on along the surface normal. This
Figure 4 shows VRweb running with NCSA Mosaic for Win-
mo de is very useful for examining details of a scene and
dows.
complements other navigation metaphors likeWalk or Flip,
A similar mechanism is b eing investigated to implement
but is not sucientasa navigation technique p er se.
inline and anchor requests over the Netscap e client API.
Heads Up is p erhaps the easiest navigation mo de for b e-
ginners, since its controls are clearly visible. Icons overlaid
across the centre of the viewing window like a pilot's heads-
4.2 VRweb and Hyp er-G
up display symb olise the individual navigation to ols: eyes
to lo ok around, a walking p erson for walking, crossed arrows
Harmony is the Hyp er-G client for Unix/X11. Anumber
for vertical and sideways motion, and a crosshair symbol to
of navigational to ols are provided, including a hierarchical
activate p oint-of-interest motion.
overview collection browser , a bidirectional link overview
Should users ever get lost, a \Reset View" function is
lo cal map , and a 3D information landscap e. Harmony sup-
available to restore the initial view of the scene. A \Level
p orts the whole range of Hyp er-G features, including link
View" function makes the current view horizontal. Other
creation in any do cument typ e. VRweb's communication
functions include op ening lo cal les, saving les, setting
with Harmony [3 ] go es through the Harmony Session Man-
preferences, changing colours, etc. The current frame rate
ager, which holds a connection to a Hyp er-G server. The
Figure 4: VRweb as a helper application with Mosaic for Windows.
Figure 5: VRweb and the Harmony client for Hyper-G. The user is navigating through a virtual model of the city of Graz. In
the background are the Harmony Session Manager and 3D Information Landscape.
Figure 6: VRweb and the Amadeus client for Hyper-G.
5 VRweb's Software Architecture Session Manager retrieves metadata and hyp erlinks directly,
do cuments themselves are retrieved along a direct connec-
Figure 8 shows the basic software architecture of VR-
tion between the do cument viewer VRweb in the case of
web. The WWW, Gopher, or Hyp er-G client communicates
VRML scenes and the Hyp er-G server. All do cuments,
via an interface layer with VRweb. The arrows indicate the
whether they come from a Hyp er-G server or through an-
owof data and control signals. The VRML data stream
other proto col like WWW or Gopher, go via the Hyp er-G
is parsed and an internal data structure constructed. Com-
server, which allows for a single do cument-viewer proto col
mands for inline scenes and anchor activations are initiated
and organisation-wide caching of do cuments. Figure 5 shows
by the link management mo dule and passed on to the clients
Harmony and VRweb with a virtual tour through through
for retrieval. The rendering comp onent manages user input
the city of Graz.
and visualises the data structure. Graphics output is done
Amadeus is the Windows client for Hyp er-G. Besides
via an abstract interface GE3D to one of several underly-
viewing all typ es of Hyp er-G media it provides easy to use
ing graphics libraries.
authoring facilities using standard Windows applications and
For parsing the VRML input stream, VRweb utilises
le formats. In the Windows environment all communica-
the freely available QvLib parser byPaul Strauss of Silicon
tion with the server is done by Amadeus, the Hyp er-G client
Graphics. It supp orts VRML to the extent of the 1.0 sp ec-
for Windows. It provides a link list, holding all anchors for
i cation and was extracted from the Inventor library. The
this do cument, which is generated at do cument selection
parser has ob ject-oriented structure and is implemented in
time. Inline scenes are handled by Amadeus using asyn-
C++. Each no de and data typ e of VRML corresp onds to a
chronous requests. Link creation is done the same wayas
class, which has generic metho ds to read the data. Metho ds
for other media typ es, e.g. text, images, PostScript. Fig-
for rendering and selecting ob jects have b een added for use
ure 6 shows Amadeus and the VRweb for Windows.
with VRweb.
Even though links in do cuments on a Hyp er-G server are
Tokeep VRweb source co de indep endent from any par-
stored in a link database separate from the do cuments them-
ticular graphics library, an abstract interface layer called
selves, link anchors contained within VRML les residing on
GE3D Graphics Engine for 3D is placed b etween the ren-
other servers are resp ected by VRweb, so as to retain com-
dering co de and the graphics library. GE3D provides func-
patibility with the rest of the Web. In the other direction,
tionality at a slightly higher level of abstraction than, say,
VRML les on a Hyp er-G server have their links merged in
Op enGL [20 ] a single GE3D call typically resulting in sev-
on-the- y, when b eing accessed from a WWW client.
eral lower-level Op enGL calls . For example, GE3D has sin-
gle functions for geometric transformations, drawing p oly-
4.3 VRweb and Gopher
hedra a set of faces with related prop erties , de ning light
sources, etc. Interface functions to window systems, like
VRweb is in the pro cess of b eing integrated into Gopher
window mapping and event handling, are kept out of GE3D,
clients, including the new three-dimensional GopherVR. Fig-
so as to achieve a high level of p ortability. These routines
ure 7 shows VRweb running with GopherVR.
Figure 7: VRweb running alongside GopherVR.
library for this purp ose would have b een easier, but would are handled in a platform-sp eci c manner within the appli-
also have limited the availability of the viewer to platforms cation.
on whichInventor is available. The approach taken allows GE3D is currently implemented for four Op enGL-like
for the optimisation and tuning of the graphics library to graphics libraries: Op enGL, IrisGL, Mesa, and VOGL an
the scop e of VRML compared to the more general-purp ose earlier version of GE3D was also p orted to Hewlett-Packard's
Inventor library. Starbase . Op enGL is the most prominent 3D graphics API,
Atop this layer, one class is resp onsible for user inter- avendor-neutral standard endorsed by many ma jor suppli-
action. For the X11 version of VRweb, the InterViews [14 ] ers. Its functions are at a relatively low level and designed
to olkit and a library of widgets built on top of it are used to for hardware acceleration. Its predecessor, GL now referred
provide menus and other user interface elements. All events, to as IrisGL , was Silicon Graphics' original proprietary 3D
like keystrokes, mouse clicks and movements, are handled graphics API. Mesa [22 ] is a freely available graphics library
and result in function activation or are mapp ed onto elemen- with an API very similar to that of Op enGL. Mesa maps
tary navigational functions provided by the Camera class, graphics calls to b oth the X-proto col and to Windows, al-
dep ending on the currentnavigation metaphor. This mo d- lowing 3D graphics rendering without any sp ecial hardware.
ular approach allows for a relatively simple p ort to another Another library with similar characteristics is VOGL: its
window system or platform, as was done for MS-Windows API is similar to IrisGL, but it lacks functions for hidden
with Visual C++. surface elimination and smo oth shading in its original im-
The interface to WWW, Gopher, and Hyp er-G clients is plementation.
encapsulated in a separate mo dule. Although they vary in
their functionality and capabilities, the di erent clients are
5.1 VRweb for Unix/X11
accessed via a common abstract interface.
The Unix version of VRweb evolved from the Harmony3D
Scene Viewer for Hyp er-G. The design follows ob ject-oriented
5.2 VRweb for Windows
principles, and is implemented in C++. The base class is the
The design goal of the Microsoft Windows version of VRweb Scene which provides abstract metho ds for loading, draw-
was to have a single source tree and one executable for each ing, picking, link management, and selection. Data man-
platform Windows 3.x, Windows 95, Windows NT on Intel, agement, including parsing and traversal to implement the
Alpha, PowerPC, and MIPS . Therefore, VRweb for Win- functions, is handled by a class dep endent on the scene le
dows is based on Microsoft's WIN32s 32-bit call interface. format.
Using WIN32s has a numb er of other advantages over the 16- For VRML scenes, the data structure built by the browser
bit Windows programming interface, such as its at memory is kept and has to b e traversed for drawing. As the struc-
mo del, higher stability, and b etter device p erformance. ture of VRML is very much tailored to the capabilities of
To render the three dimensional scenes we used Op enGL Op enGL, the mapping of VRML primitives to the drawing
atalow level and the GE3D library at a higher level, thus commands of GE3D is straightforward. Using the Inventor
Availability
Clients 6
VRweb is available b oth in binary and in source co de for
ariety of platforms. The source co de is copyrighted, but
WWW Gopher Hyper−G av
is freely available for non-commercial use see the copyright
notice with the distribution for full details . VRweb co de is
available by anonymous ftp from: ftp://ftp.iicm.tu-graz.ac.at/pu b/Hy per-G /VRw eb
Interface Layer ftp://ftp.ncsa.uiuc.edu/Hyper-G /VRw eb
ftp://boombox.micro.umn.edu/pub /Hyp er-G/ VRwe b
as well as from a numb er of other mirror sites. There is a
VRweb technical home page with up-to-date technical in- formation at:
VRML Parser Link Management
http://info.iicm.tu-graz.ac.at/ Cvrw eb
gopher://info.iicm.tu-graz.ac.a t/ hyperg://info.iicm.tu-graz.ac.a t/vr web
Rendering
The VRweb mailing list is the place for questions, sugges-
tions, and discussion of VRweb. To subscrib e to the mailing
list, send email to: [email protected]
GE3D
with message b o dy no sub ject needed :
subscribe vrweb FirstName LastName
Graphics Library
o unsubscrib e, mail \unsubscribe vrweb" to the same ad-
OpenGL, IrisGL, Mesa, VOGL T
dress. To send mail to all memb ers of the list, simply com-
p ose your message or question and send it to:
Figure 8: VRweb's softwarearchitecture.
7 Concluding Remarks
staying compatible with the UNIX versions of VRweb. De-
p ending on the system capabilities, either original Microsoft
In order to rmly establish VRML as the standard for three-
Op enGL for Windows NT and Windows 95, p ossibly with
dimensional scenes on the Internet, it is not sucienttohave
hardware acceleration and/or the public domain libraries
a go o d language sp eci cation. Viewers capable of many pro-
Mesa and VOGL software-only rendering may be used.
to cols and implemented on many platforms are necessary.
The University of Minnesota extended the VOGL library
Another crucial p oint is the free availability of source co de
with a binary space partitioning BSP algorithm for faster
for non-commercial organisations to allow research and ex-
hidden surface elimination for details on BSP see [11 ] . The
p erimentation with this new typ e of media. These were the
Mesa library was enhanced by an additional rendering mo de
design goals of VRweb.
for the Windows driver using RGB colours and a 256 colour
Future areas of research will include the incorp oration
palette with index addressing. This mo de uses the WING
of collision detection for more realistic navigation, visibility
library whichwas designed esp ecially for fast bitmap display.
prepro cessing to sp eed up rendering esp ecially on slower
The architecture of VRweb for Windows is based on the
machines , and editing functionality for home space con-
Windows Multiple Do cumentInterface MDI and the Mi-
struction. We hop e that the availabilityofanopendevelop-
crosoft Foundation Classes MFC . This makes integration
ment platform will contribute signi cantly to the evolution
into other environments very easy. The VRweb viewer is
of the VRML standard.
fully integrated into Amadeus, the Hyp er-G client for Win-
dows. It will also interface with Mosaic and the Gopher
client. A stand-alone version is available using the same
8 Acknowledgements
co de but not providing any link or inline facilities. Ho oks
for these functions are provided in the source co de, so any-
The authors are grateful to Brian Paul for helpful discussions
one can implement them for a proprietary target platform.
regarding the Mesa library and would like to thank all of the
The user interface is similar to that of VRweb for X11, but
memb ers of the Hyp er-G, NCSA, and Gopher teams for their
has Windows lo ok and feel.
dedication and fruitful collab oration on the VRweb pro ject.
The I ICM work on VRweb is partially nanced by the
Anniversary Fund of the Austrian National Bank, under
5.3 VRweb for Macintosh
pro ject numb er 5334, \Virtual Information Spaces".
A p ort of VRweb for the Macintosh is underway and is ex-
p ected to b e available by the time this pap er is published.
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