7. Future work
The National HPCC Software Exchange
is funded by NASA
as part of the High Performance Computing and Communications (HPCC)
program, established in 1991.
NASA's primary role in the HPCC program is to lead the development
of applications software and algorithms for scalable parallel computing
systems. NASA is also responsible for fostering software sharing
and reuse across federal HPCC programs.
NHSE provides access to all software and
software-related artifacts produced by the HPCC Advanced Software
Technology and Algorithms (ASTA) component.
Access is provided in a manner that promotes
and facilitates reuse and technology transfer policies and processes
established by HPCC program agencies. The NHSE provides
a uniform interface to a distributed collection of networked
repositories, which for administrative and logistical reasons
are maintained separately. The NHSE achieves
sophisticated searching and retrieval while
imposing only minimal delay between the production and distribution
of software artifacts.
Although the different disciplines will maintain their own software
repositories, users need not access each of these repositories
separately. Rather, the NHSE provides a uniform interface to a
virtual HPCC software repository that will be built on top of
the distributed set of discipline-oriented repositories.
The interface assists the user in locating relevant resources
and in retrieving these resources.
A combined browse/search interface allows the user to explore
the various HPCC areas and to become familiar with the available resources.
A long-term goal of the NHSE is to provide users with domain-specific
expert help in locating and understanding relevant resources.
The target audiences for the
NHSE include HPCC application scientists, computer scientists, users of
government supercomputer centers, and industrial users.
The expected benefits from the NHSE
The scope of the NHSE is software
and software-related artifacts produced by and for the
Software-related artifacts include algorithms, specifications,
designs, and software documentation.
The following types
of software are being made available:
- Faster development of high quality software so that
scientists can spend less time writing and debugging programs
and more time on research problems.
- Reduction of duplication of software development effort
by sharing of software modules.
- Reduction of time and effort spent in locating relevant
software and information through the use of appropriate indexing
and search mechanisms and domain-specific expert help systems.
- Reduction of the time scientists spend dealing with
information overload through the use of filters and automatic
The NHSE went on-line in February of 1994. Since that time, there
have been over 160,000 accesses to the NHSE pages residing at
the University of Tennessee. Comprehensive
usage statistics for the NHSE at the University of Tennessee
may be viewed on-line in graphical format.
A snapshot as of April 1, 1994, is shown in Figure 1.
Geographical usage maps
produced by a mapping system developed at Argonne National Laboratory
are also available.
- Systems software and software tools.
This category includes parallel processing tools such as parallel
compilers, message-passing communication subsystems, and parallel
monitors and debuggers.
- Data analysis and visualization tools.
- High-quality transportable building blocks for accomplishing
common computational and communication tasks.
These building blocks are meant to be used
by Grand Challenge teams and other researchers in implementing
programs to solve computational problems. Use of high-quality
transportable components will speed implementation and will
increase the reliability of computed results.
- Research codes that have been developed to solve difficult
computational problems. Many of these codes will have been
developed to solve specific problems and thus will not be reusable as is.
Rather, they will serve as proofs of concept and as models for
developing general-purpose reusable software for solving
broader classes of problems.
The current NHSE information collection has been constructed by manually
generating and maintaining sets of HTML pages at the different
CRPC sites. These pages contain information about HPCC, as well
as pointers to external URLs relevant to HPCC.
The NHSE home page,
as well as an index to the distributed NHSE information collection,
is maintained at the University of Tennessee site. Other sites
with large collections of NHSE URLs include
NPAC at Syracuse University, Argonne National Laboratory,
and Rice University.
Figure 1: NHSE Usage Statistics
The URLs were discovered by contacting groups and individuals
active in HPCC, by searching for HPCC-related information
on the Web, and by soliciting user contributions.
The URLs have been organized into categories and sub-categories
to facilitate browsing. The major categories include
HPCC programs and activities, Grand Challenge applications,
software repositories, and several sub-categories for
individual software packages.
Close to 700 URLs have been collected, and more are added every day.
Many of these top-level URLs are lists that point to other
relevant URLs. By going just two levels down from the NHSE home
page, the user may access a total of over 10,000 HTML pages
relevant to HPCC.
The Harvest system .
provides the search interface to the NHSE collection.
A Harvest gatherer running at the University of Tennessee
retrieves all URLs pointed to by the NHSE, plus one additional level --
in other words, three levels of a breadth-first search tree
rooted at the NHSE home page. A Harvest broker indexes the files
using WAIS and provides a query interface for keyword searching.
Other sites will soon be running Harvest gatherers as well,
so that deeper and more comprehensive
indexing may be carried out. Because gatherers stream summary information
to brokers, rather than sending files individually,
such a distributed setup permits efficient use of
As the NHSE broker becomes more heavily used in the future,
it is likely to become overloaded. To deal with this problem,
Harvest provides for broker replication. We will monitor the load
on the NHSE broker and replicate as needed.
As part of the research in enabling technologies for the NHSE, Argonne is
building a toolkit for exploring advanced Web resource management
technologies. The toolkit will support hunting and gathering Web pages
(http, ftp, gopher), compression, indexing, transaction monitoring, parallel
search and a rich language environment for developing agents.
The toolkit includes a modular Web forager, a parallel Web indexing
engine, and autonomous search agents.
The modular programmable Web forager is designed to efficiently
cache Web pages on a local server, based on programmable starting
locations, keywords, file types, and other search criteria.
The Web forager runs in parallel to allow high-performance gathering
of Web pages. Its modular design allows it to be easily modified.
3.1 Operation of the Web Forager
A schematic of the Web forager is shown in Figure 2.
The following algorithm is the basis for the forager:
Figure 2: Argonne Web Forager Architecture
There are several large data structures implied by the above
algorithm: a pool of URLs to be searched, an index of retrieved pages,
and possibly a local cache of the full text of the Web pages. These
data structures can become quite large. In a large-scale run of the forager,
one can expect several million URLs in the pool. This implies a
need for over a gigabyte of storage for the URL pool alone.
- Initialize the URL pool
- While there are pages in the pool
- Remove a URL from the pool
- Download that page from the Web
- Parse the page, generating a new list of URLs. Add these URLs to the pool.
- Index the page
- If caching, save the page locally
We maintain a database of information about the URLs that have
been visited (the meta-database). The information is kept on a per-URL
basis and includes
We also maintain a database of information about the Web servers
involved in the search (the host database).
This database includes information such as
- Date page retrieved
- Last modification date of document on server
- Document type
- Retrieval frequency
- Expiration date
Note that the last item is the URL pool referred to above. We maintain
the URL pool on a per-host basis to reduce the size of the
pool and to provide a convenient way to structure the search.
The forager algorithm can now be presented in more detail:
- Last time host was contacted
- Preferred interval between accesses to host
- List of URLs to be searched
Note that there are two decisions to be made: which host should be
searched, and which URL from the pool of URLs for that host should be
that implement custom strategies for these decisions. For instance, a
``hotlist'' of URLs may be maintained, to be searched more often than
the general pool.
One of the goals of the forager project is to complete a five million
URL forage in a week. Such a run introduces two obstacles: network
latencies and the necessity of handling large databases.
- Initialize the URL pool
- While there are URLs to be searched
- Pick a host to search
- Remove a URL from that host's URL pool in the host database
- Download that page from the Web
- Parse the page, generating a new list of URLs.
- Update the meta-database with each new URL
- Add each URL to its host's URL pool in the host database
- Index the page
- If caching, save the page locally
- Update the meta-database entry for the searched URL
We have seen from our experiments with a sequential forager that most
of the time spent in the forager is spent in waiting for the wide area
network -- over eighty percent of a recent run. Because in a large run
there will be a large number of servers from which to retrieve pages,
we can very efficiently utilize multiple foragers to overlap useful
computation and the time spent waiting on the network. The forager
processes are very lightweight, carrying little state information. As
a result we can usefully run multiple foragers on each node in the
The size of the databases required for a five million URL forage
introduce some practical problems. We want to keep the
databases in memory as much as possible, as the operation of the
forager requires both frequent lookups into the databases (for URL
pool and host information) and frequent updates to the databases
(new entries to the URL pool, updates to the metadatabase). We
anticipate a metadatabase size of over 1.5 gigabytes (not including
the URL pools). The parallel forager distributes the meta- and
hostdatabases across several computers, reducing the size of the
individual databases to the point that much of the database will be
cachable in memory.
We have taken great care in the design of the forager to make it a
good network citizen.
Other web robots have caused problems by making rapid-fire requests
to a single server, repeatedly requesting the same file from a server,
or by making large numbers of meaningless requests (for instance,
making deep traversals in virtual trees or by invoking CGI scripts
with side effects).
These problems led to the development of the
Standard for Robot Exclusion .
The NHSE web forager is compliant
with this standard.
We also adhere to the philosophy that the forager should be no more
intrusive than a human browsing the web. We implement this
by allowing the forager to access any
given host for only a short period of time (defaulting to thirty seconds)
before moving on to the next host.
Once a search has been running for
a while, there are enough hosts to be searched that the search
frequency for any given host is not high.
In addition, host-specific requirements (search frequency, interval
between successive request, and so on) can be specified on a per-host
basis in the case that the default policy is not appropriate.
The Web forager is written in
Perl 5 
for modularity and rapid prototyping. Communication is handled
by using Nexus ,
which provides remote procedure call semantics,
threading support, remote reference support, and clean integration
with Perl 5.
is via the DB_File interface module 
Berkeley DB library ,
which provides disk-based databases with efficient in-memory
The modular design of the forager permits the developer to plug
in per-document-type handler modules, as well as per-protocol
Argonne is also developing a parallel extension of the
Glimpse (University of Arizona)
indexing system 
for rapidly indexing web pages (*.html and
other file types) on parallel systems and for providing rapid regular
expression based parallel searches of Web page caches, such as those
generated by our Web forager. We are also developing extensions to the
query system specifically allowing us to locate "software" in the
midst of other Web information, thus supporting the ability to search
for data that contains software (source files, binaries, tar files,
makefiles etc.) across the Web. This Web indexing engine should in
principle be scalable to millions of URLs. A five million URL test
run is planned for the near future.
The indexing structure distributes indices across multiple index
nodes, allowing lookups to be carried out in parallel.
Content pages may be discarded after indexing, because the
Glimpse indexing mechanism can be used to identify URLs to
be retrieved for further filtering.
A Web form-based search interface is provided.
The most recent
testbed search database, collected January 25 - 29 1995,
contains 52032 URLs, including 37700 HTML pages, from 13000 sites.
To generate this database, the Web forager was started
from the Argonne Mathematics and Computer Science Division home page.
Contributors submit software to the NHSE by filling out
the NHSE Software Submission Form, accessible from the
This form explains the submission and review process, including
the authentication procedures, and gives an example of a completed
submission form. The form asks the user to fill in values for
several attributes, some required and some optional.
Contributors submit software for consideration at a particular
Currently three levels of software are recognized in the NHSE:
To receive the Partially reviewed rating, software submitted to the NHSE
should conform to the following guidelines:
- Unreviewed. The submission has not been reviewed by the NHSE for
conformance with software guidelines. This classification is for unreviewed
software available on an ``as is'' basis.
- Partially reviewed. The submission has undergone a partial NHSE
review to verify conformance with the scope, completeness,
documentation, and construction guidelines. These particular
guidelines are those that can be verified through a visual inspection of
- Reviewed.The submission has undergone a complete NHSE review
to verify conformance with all the software guidelines. This
classification requires peer-review testing of the submitted software.
This level may be further refined into additional levels
in the future.
To be accorded the reviewed status, the software must first have been
accorded the partially reviewed status. This precondition ensures that
reviewers will be able to access all the information needed to carry out the
review over the National Information Infrastructure.
- Scope. Software submitted to the NHSE should
provide a new capability in numerical or high-performance
computation or in support of those disciplines.
- Completeness. Submissions must include all routines and
drivers necessary for users to run the software.
Test problem sets and corresponding drivers must be
included if the
software is to undergo peer-review testing for
the Reviewed level.
Source code for widely
available software used by the submission, blas and
lapack for example, need not be included as part
of the submission.
- Documentation. The software contains complete and understandable
documentation on its use.
- Construction. Submissions must adhere to good mathematical
software programming practice and, where feasible,
to language standards. Software should be constructed
in a modular fashion to facilitate reusability.
The use of language checking tools, such as
pfort or ftnchek, is recommended.
Software submitted for full review is reviewed according to the
After software has been submitted for full review,
it is assigned to an area editor, who recruits two to six reviewers to
peer review the software according the above criteria.
To qualify for full review,
an author must provide sample data and the output from or a
description of results from each sample. Each reviewer is asked to read
the software documentation and try the software on some of the data sets
provided by the author. In addition, it is recommended that a reviewer test the
software on inputs not provided by the author.
If source is available, the reviewer
examines the source to ensure that the methods and programming
methodology are of acceptable quality. Each reviewer prepares all
comments in electronic form and returns these, along with a recommendation to
the editor in charge of the review.
After the peer reviews are returned, the editor makes the final decision
as to whether to accept the software and informs the author of the decision.
If the software is accepted, the area
editor prepares a review abstract for use by the NHSE.
The software contains complete, understandable, correct
documentation on its use.
The software is relatively bug-free and works as advertised on
all provided data sets and on data sets provided by the reviewer according
to the documentation..
The methods employed by the software are sound for solving the
problem it is designed for, as described in the documentation.
The software has an understandable user interface and is easy to
use by a typical NHSE user.
The software runs sufficiently fast to make it an effective tool.
Once the software has been reviewed, one of two things happens.
If it is not accepted,
the author will be so informed and anonymous copies of the reviews
will be provided.
The author may then choose to address the reviewers' comments and
resubmit revised software.
If the software is accepted, the author will be shown a review abstract
summarizing the reviewer comments. This abstract will be available to anyone
who accesses the software through the NHSE. If the author finds the abstract
unacceptable, he or she may withdraw the software and resubmit it for review
at a later date.
After they have been processed, software submissions are placed
into the NHSE software catalog.
The cataloging process is carried out jointly by the
authors and the NHSE librarian, with the authors providing the
title and abstract fields, and the NHSE librarian categorizing
each entry and assigning thesaurus keywords. The NHSE software catalog
is available in the following formats:
A user may submit a user profile by filling out the
NHSE User Profile Submission Form, accessible from the
This form asks the user about his or her background,
interests, and software and information needs.
Although name and email address are requested so that
a reply can be made, a user profile is kept confidential
unless the user gives permission to publish it.
- An HTML version that may be browsed by category.
- A searchable version that allows the user to search separately
by different attributes or to do a free-text search on the catalog
A link to an on-line copy of the HPCC thesaurus is provided so that
users may select controlled vocabulary terms for searching.
The current interface requires users to cut and paste thesaurus
terms into the search form. We plan to develop a hypertext version of
the thesaurus that will statically link thesaurus terms to scope and
definition notes and to related terms
as well as dynamically link thesaurus terms to indexed
- A PostScript version that may be downloaded and printed.
The purpose of collecting user profiles is two-fold:
Responses according to user profiles are currently made by a
NHSE librarian who searches for relevant information and
constructs a customized reply. In the future, automatic
foraging and filtering techniques will be used to automate
the reply process.
Researchers at Argonne National Laboratory are developing
autonomous search agents that will have the capability
of building comprehensive databases of available information
meeting particular search criteria, and of providing the
user with updates regarding changes made to this database.
- To serve NHSE users by providing customized responses
to requests for information.
- To collect a sample database of profiles to use for
comparative testing of different search strategies.
The user profile database will also provide a test query set
for evaluating the recall and precision of the following
An HPCC thesaurus is currently under development as part of
the NHSE development effort.
This thesaurus is being developed according to the ISO 2788
thesaurus standards 
using a faceted construction technique
 for the core area of mathematical software.
Other sources of vocabulary for the core areas are the
current NHSE contents, the HPCC glossaries described below,
and the book
Parallel Computing Works .
- natural language processing (NLP)  alone
- Latent Semantic Indexing (LSI) alone
- LSI with NLP noun phrase extraction as a preprocessing step
- using the HPCC thesaurus for both manual indexing and searching with
- using the HPCC thesaurus as a searching thesaurus only for boolean
- NLP assisted by thesaurus scope notes and definitions
- LSI assisted by thesaurus scope notes and definitions
The HPCC thesaurus is intended to be used directly by NHSE users
rather than by expert search intermediaries. Therefore, the
use of complex devices will be minimized, and extensive scope notes
and definitions of thesaurus terms will be provided.
Thesaurus terms will be assigned manually to NHSE Software Catalog
entries by the NHSE librarian as part of the submission process.
Although the larger body of NHSE informational HTML pages will
not be indexed manually, the thesaurus will still be useful
for searching this collection, as it will provide an overview
of the field and will supply candidate
terms for searching.
In view of the positive reception of our HTML glossary on HPCC
terminology at Supercomputing 94, we have developed new
other subjects relevant to the NHSE. In particular we are
building general glossaries on HPCC applications areas, HPCC software
technologies, and specialist glossaries of terms and keywords in High
We have given a lot of thought to the concept of a glossary and on how
it relates to other ways of packaging information on the WWW. The
traditional glossary is a way of explaining ``jargon'' in a textbook
and is distinguished from other alphabetically sorted lists of
definitions such as dictionaries, encyclopedias and thesauri not only
by the ``granularity'' of the information entities but also by the way
entries are cross referenced. Conventionally, a glossary lists
definitions of keywords, acronyms or key phrases in a fairly informal
prose style, with cross references (if any) indicated by italic or some
other form of printing emphasis. Our HTML glossaries are written in a
similar style, with italic font used to indicate internal cross
references and bold font for external references. The main
distinguishing feature is that the HTML form allows the references to
be URLs, either internal ones in the hash format, or full http form
external references to other information entities on the Web.
We view the glossary form as a good form to encapsulate domain level
expertise on a particular subject, whether that be a broad subject
such as HPCC or a narrower subject such as the particular HPCC
terminology associated with High Performance Fortran
One disadvantage of the glossary form is its non-scalability. To be
successful a glossary has to be written from a particular point of
view and must have a consistent philosophy. We believe this is
relatively straightforward when the subject covered is such that an
individual or a small editorial team can carry out the entire review
process. This becomes harder for multi-disciplinary subjects such as
``HPCC Applications''. For this reason we are currently working on
ways of linking the glossary and thesaurus concepts into a consistent
hierarchy of information systems.
We envisage the following conceptual hierarchy of information granules:
Ideally, the NHSE roadmaps and navigation aids should
appear to have been written to match the knowledge background of the user as
closely as possible. We believe this is the best approach for
successful exploitation of a new technology such as HPCC.
- Specific real items of software for applications, libraries,
tools, languages, or environments.
- Hypertext ``Encyclopedia articles'' that are written from a particular
perspective, and are essentially review articles or technical notes.
- Glossaries that are essentially ``hypertext expert systems'' or
review articles with a lower granularity than encyclopedia articles.
- Thesauri, which are generalized cross referencing mechanisms,
coupled to search engines.
The HPCC glossary was first initiated as an HTML document with hand
written entries with embedded HTML tags. This approach is both
cumbersome and error prone.
To partially solve these difficulties we have developed a scripting tool
that parses entries and flags incorrectly formatted entries and makes
checklists of internal, external, and duplicated entries. However, as
the HPCC glossary alone has grown to over 700 definitions,
this approach is no longer scalable, since it becomes increasingly
difficult for a human being to keep track of the possible cross
references when writing a new entry. We have developed textual
analysis tools to aid the entry writer in cross referencing a new
entry. We are using hypertext technology for this in the form of
client data forms that invoke word stemming and other analysis
programs on the server side. The word stemming process is required so
that duplicate cross references are not necessary for an entry that
might be ``cache'', ``caches'', ``cached'', or ``caching'' for example.
We have built tools that can parse glossary entries from manually
edited hypertext, as well as from HTML forms.
The resulting entries may be input
directly into the on-line glossary system or submitted
to an editorial review board.
We have developed a general roadmap
navigation package to HPCC related sites and activities with an
attempt to link applications activities to software and other
technical information stored in the NHSE. We are currently
integrating this with the glossary and thesaurus systems.
The NHSE roadmaps and glossaries are all accessible
from the "roadmap" link on the NHSE home page.
In our manual information collection, we evaluate contributed HTML
pages and only add those to our collection that are within the
scope of high performance computing. When browsing the Web manually
to collect information, we selectively follow those links that appear
most relevant. As currently implemented, our Web forager, when started
from a particular location, follows all links with equal likelihood.
We plan to extend the forager with filtering mechanisms, based
on keywords, file types, and semantic analysis. These heuristics
will enable selective retrieval of the most relevant information.
Semantic analysis using techniques such as LSI 
will allow automatic selection of documents that are similar,
or "close in the concept space", to the manually selected collection.
An option of an interface interface with a human operator will allow
human feedback to guide the forager's Web traversal.
Classification and cross-referencing tasks take place at several
points in the NHSE's information management processes.
When a contributor submits a new software package, the
NHSE librarian places it into the appropriate category and
assigns thesaurus keywords. Newly contributed URLs for Web pages
are placed on the appropriate list on the appropriate NHSE page.
New HPCC glossary entries are cross-referenced to existing entries
and to external material.
Now that a fair amount of manual classification
has been carried out, we are in a position to begin partially
automating the classification process.
Using both previously classified material and newly contributed material
as inputs, semantic analysis techniques may be used to suggest appropriate
classifications for the new material. Preliminary experiments we have
carried out using LSI to generate candidate GAMS classifications
for mathematical software have shown close agreement with the
classifications assigned by human experts.
Although LSI and related techniques are not accurate enough
to completely automate the classification process, partial
automation will allow a much larger amount of material to be
processed with the same manpower, and may reveal unexpected linkages
that would have been missed by human classifiers.
As with most current Web search services, the current NHSE
search interfaces are limited to keyword searching. Because of
vocabulary mismatch problems, and because users are unsure what
keywords to enter, free-text keyword searching results in poor
recall. Recall can be improved by allowing the user to iteratively refine
a search and to apply relevance feedback to search results.
We plan to implement relevance feedback capabilities for our search
interfaces that will allow the user to select one or more items
of particular interest for the purpose of augmenting a previous search.
Both the NTTC natural language processing 
and the LSI search engines provide this capability, and we will
be experimenting with both of these systems.
Automatic filtering and profiling techniques that are purely
keyword based have shown poor results, because of vocabulary
mismatch problems, but also because the relevance of a particular
item is often implicit in its context. We plan to use semantic
analysis, augmented by relevance from users, to automate foraging
of information to match submitted user profiles.
Some previous work in this area is described in .
Jean Aitchison and Alan Gilchrist.
Thesaurus Construction: A Practical Manual, 2nd ed.
Aslib, London, 1987.
Ronald F. Boisvert and S. E. Howe and D. K. Kahaner.
The Guide to Available Mathematical Software problem classification
system, Comm. Stat. - Simul. Comp. 20(4), 1991, pp. 811-842.
(GAMS is available on-line at http://gams.nist.gov).
C. Mic Bowman, Peter B. Danzig, Darren R. Hardy, Udi Manber, Michael F.
Schwartz, and Duane P. Wessels. Harvest: A Scalable, Customizable
Discovery and Access System. Technical Report CU-CS-732-94,
Department of Computer Science, University of Colorado, Boulder, August
1994 (revised March 1995).
S. Deerwester and S. Dumais and G. Furnas and T. Landauer
and R. Harshamn. Indexing by Latent Semantic Analysis.
Journal of the Americal Society for Information Science 41(6),
September 1990, pp. 391-407.
Peter W. Foltz and Susan T. Dumais. Personalized Information Delivery: An
Analysis of Information-Filtering Methods. Communications of the ACM
December 1992, pp. 51-60.
Ian Foster, Carl Kesselman, and Steven Tuecke.
Nexus: Runtime Support for Task-Parallel Programming Languages.
Technical Memo ANL/MCS-TM-205, Argonne National Laboratory, 1995.
Geoffrey C. Fox, Roy D. Williams, and Paul C. Messina.
Parallel Computing Works. Morgan Kaufmann, 1994.
(available on-line at http://www.infomall.org/npac/pcw/).
International Organization for Standardization. ISO 2788:
Guidelines for the establishment and development of monolingual
thesauri, 2nd ed. Geneva: ISO, 1986.
Martijn Koster. A Standard for Robot Exclusion.
Udi Manber, Sun Wu, and Burra Gopal.
Glimpse: A tool to search entire file systems.
Paul Marquess. DB_File - Perl5 access to Berkeley DB.
NTTC Digital Library: A Robust, Replicable Package.
INFOTECH '94: DOE Technical Information Meeting, Office of
Scientific and Technical Information, October 1994,
Margo Seltzer and Ozan Yigit. A New Hashing Package for UNIX.
USENIX, Winter 1991, Dallas, Texas. (BerkeleyDB is available at
Larry Wall. Perl 5 Manual.
April 3, 1995