Access to the HEASARC on Legacy

via Anonymous ftp, Gopher,

WWW, and ADS

Introduction

The data and software archive that is being maintained by the NASA/Goddard Space Flight Center's HEASARC (High Energy Astrophysics Science Archival Research Center on its legacy computer is now accessible to the user community via at least 5 different paths:

(i) Using the File Transfer Protocol (ftp) tool (as discussed in detail by Drake and O'Neel in the last issue of Legacy);
(ii) Using the Internet Gopher (Gopher);
(iii) Through the World-Wide-Web (WWW) and Mosaic method;
(iv) Using NASA's Astrophysics Data System (ADS); and

Even though this plethora of options may seem excessive, we believe that it is important to offer multiple protocol access to our archives: which one the user should choose depends on individual preferences, degree of expertise with these various systems, and on the software that is available on the user's own machine. These different ways of accessing our data can, in fact, be interlinked: for example, within the WWW environment, the user also has the option of accessing us by all the other methods! In this article we will discuss these various access methods in more detail, present what we feel are the advantages, disadvantages, and/or limitations of each one, and conclude by stating on which of these services we expect our future activity to be concentrated.

General Considerations Concerning Electronic Information Services

In order to use any of these services, a user's computer must be on a computer network such as Internet or NSI/DECnet. ftp, Gopher, and WWW all require that the user's machine has the appropriate local software, the so-called 'client' program, installed on it. When activated and told to contact our database on legacy, this client software interacts with the appropriate 'server' software on our machine, sends queries to it, and receives and displays the responses from the server.

Access via ftp to legacy

This was extensively discussed in the last issue of Legacy (Drake and O'Neel 1993, 3, 53). The user must simply type ftp heasarc.gsfc.nasa.gov and, when prompted, log on as anonymous (or ftp). ftp is a command-driven program in the traditional style with no graphical capabilities: to list the contents of a directory, one types the command 'ls' or 'dir', to change to another directory called fred, one types 'cd fred', etc. A short ASCII text file called ftp_hints.asc in the top-level directory contains a brief discussion of common problems (and their solutions) and some hints that we hope might help an inexperienced user of anonymous ftp. As stated in the previous article on the anonymous ftp account, we always recommend that a user who is accessing a directory for the first time read the relevant README files. The short message that pops up when you cd into a directory (the .message file) also often contains important information. The welcome message to the anonymous ftp account that appears after you log in to the account is also 'must' reading as we use it to announce major changes and/or enhancements to our database and also to give advance warning of planned down-times and configuration changes.

The advantages of ftp are that most users are familiar with it and have access to a local computer on which it is installed, and that its commands are very similar to standard Unix commands. The disadvantages are its lack of graphics capability, as well as its limited capability to allow a user to see what the contents of a file are without having to transfer it to his/her own computer.

Access via GOPHER to legacy

Recently, the HEASARC installed a Gopher server on legacy that supports access to the database through Gopher clients. Gopher was developed at the University of Minnesota in 1991 and adds the attributes of a graphical user interface to an anonymous ftp account, as well as having several additional features that make it much more convenient than ftp:

(i) The ability to create bookmarks marking locations in a directory tree that a user might frequently want to access. Once created, this enables the user to move straight to this area without having to go through multiple steps.

(ii) The ability to spawn programs on the users' own computer.

(iii) The ability to display files immediately so that they can be previewed: the user can route non-text files such as PostScript files through a display program such as GhostScript so that whole documents including figures and equations can be perused.

(iv) The ability to do searches in a directory for files with names containing the specified alphanumeric string.

(v) The ability to connect to other Internet services without having to know details such as e-mail addresses or node names. For example, if one Gophers to the main NASA/Goddard Space Flight Center Gopher (gopher.gsfc.nasa.gov), one can, by clicking on the appropriate option, transfer to the HEASARC Gopher server.

To use the HEASARC Gopher utility, you (or your system administrator) will have to install the Gopher client software on your home system. You can get the Gopher client software from either boombox.micro.umn.edu (138.84.132.2) or from heasarc.gsfc.nasa.gov. There are Gopher clients for MS-DOS, Macintosh, NeXT, Unix, VMS, Windows, MVS, and OS/2systems. Once you have Gopher installed on your system, you connect via Gopher to the HEASARC Gopher by typing:

gopher heasarc.gsfc.nasa.gov (or gopher heasarc.gsfc.nasa.gov).

The HEASARC gopher server is now quite stable and reliable: we encourage users to try it out, and to send any comments or criticisms concerning its performance to Bruce O'Neel at oneel@lheavx.gsfc.nasa.gov.

Access via ADS to legacy

NASA's Astrophysics Data System (ADS) is a distributed data-retrieval system that provides access to heterogeneous, geographically distributed databases and services. The ADS is designed so that the researcher does not have to know where specific data are located or in what form or on what medium they are stored, nor does the user have to be concerned with becoming proficient in the use of unfamiliar hardware and software. The ADS provides a consistent graphical user interface (GUI) to this distributed set of data and other services, and a consistent method with which to interact with them, regardless of their geographic location. The ADS consists of operational sites providing authentication, routing, and other system services, a set of host nodes that provide the catalogs, archival data, and other services, and a set of user nodes. The ADS does not own these data but provides a consistent interface to the data. HEASARC is currently one of 9 host nodes and is the primary node for access to high-energy astrophysics data. Other ADS services that the researcher may find useful are access routes to the Sets of Identifications, Measurements, and Bibliography for Astronomical Data (SIMBAD) at the Centre de Donnees astronomiques de Strasbourg (CDS), to the NASA/IPAC Extragalactic Database (NED) at the Infrared Processing and Analysis Center (IPAC), and to NASA's RECON abstract service. In order to become a registered ADS user, contact the ADS User Support Office at CASA, Campus Box 389, University of Colorado, Boulder, CO 80309 (or by e-mail at ads@cuads.colorado.edu) and they will send you an ADS User Registration Form.

Access via the WWW to legacy

Another way to access the HEASARC on-line data is via the World Wide Web (WWW). The Web is a distributed hypermedia system that was initiated at CERN in Switzerland. There are a number of WWW clients, such as the Mosaic software developed at NCSA (National Center for Supercomputing Applications), that provide access to the Web as well as having additional useful features. Looked at most simply, NCSA's Mosaic is a GUI that provides a way of unifying numerous services, such as viewing structured documents written in HTML (HyperText Markup Language), with anonymous ftp, WAIS (Wide Area Information Server), ADS (Astrophysics Data System), Gopher services, and many others, by wrapping them up in one common interface. The Web/Mosaic system is so versatile that we expect that it will soon be the dominant way in which most databases such as ours are accessed. Its outstanding features include:

(i) Its hypermedia capabilities: the user can view text, figures, color images, and movies, as well as listen to audio features. Many of these features do require additional (usually general domain) software (e.g., to get full image display capability requires having JPEGView and /or GIFConverter), but these are generally readily available.

(ii) Its vast number of interconnections with information services all over the globe.

(iii) Its amazingly straightforward GUI, which generally requires a user only to 'point and click' in order to get something. For example, in Figure 1, we show the (first part of the) HEASARC page accessible on WWW/Mosaic. Any item that is underlined is an anchor or hyperlink to either the page describing that item, or, in some cases, to another type of service. Clicking on the item 'HEASARC's Gopher server' will connect the user to the Gopher server; clicking on 'HEASARC's Online Service' will connect the user to our standard on-line service; clicking on 'Images' moves the user to the 'Images from High-Energy Astrophysics' page, where the user can select a particular mission such as ROSAT (again by clicking), and move to the ROSAT Images page where the user is presented with a list of images (small pictures that give an idea of what the full image contains), and their captions [See Fig. 2]; clicking on a caption will trigger a request for the full image which can then be displayed using one of the above mentioned image display programs.

The principal disadvantage of the WWW, if it can be so described, is that it allows the user to access vast amounts of data very easily, and the data transfer rate can, in consequence, be very slow, and the data storage of the user's own computer (if it is a little Mac, for example) can be taxed. Given the increasing availability of high data rate connections and the growing memory and processing time capabilities of most computers, we believe that this disadvantage is a minor one compared to the WWW's manifold advantages.

If you would like to experiment with the WWW before committing yourself, there are several different places to which you can telnet as a way of finding out how to start off; then, once you have been 'hooked', you can download and install your local client and display software and have a much more sophisticated interface to WWW. To get started, you can telnet to www.njit.edu and log in as www. Once you reach the page titled NJIT INFORMATION TECHNOLOGY ENTRY POINT, you should type

G http://heasarc.gsfc.nasa.gov

and you will get to the HEASARC's WWW server. This provides full access to the HEASARC on-line data, as well as to other HEASARC and astronomy specific databases. The software for the much more powerful Mosaic interface to WWW can be obtained from the NCSA. There are different versions of Mosaic for X11, Macintosh and Microsoft Windows that can all be obtained from ftp.ncsa.uiuc.edu. Once Mosaic has been installed on your local computer, you can access the HEASARC at http://heasarc.gsfc.nasa.gov or by going to the NASA page, clicking on Goddard Space Flight Center (GSFC), and then, on the GSFC page, clicking on the HEASARC. Just as for our gopher server, the HEASARC's WWW server is relatively new, and all user comments and/or questions about its present or planned capabilities are solicited, and should be sent to Alan Richmond at richmond@guinan.gsfc.nasa.gov.

Conclusions

We believe that the WWW facility is going to be the preferred access route to most databases such as ours for the foreseeable future. With this in mind, we are presently building our next-generation Browse On-line Service (a.k.a. W3Browse), that will run under the WWW. This will have most of the functionalities of BROWSE but be GUI-driven rather than command-line driven, and, of course, have additional new features, e.g. on-line hypertext documentation, an on-line feedback form, an SQL gateway, fast access & search of bulletins, more tools, FITS and GIF images automatically triggering display/analysis tools such as SAOimage. Some of these features represent a profound new way of doing business, and just have to be seen in action to be fully appreciated.

We encourage our users to try out the WWW. For the foreseeable future, we will also support the other access routes to our database, but their capabilities will probably remain static, whereas the WWW's will undoubtedly continue to grow.

Figure 1. HEASARC Home Page on Mosaic/WWW.

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