\begindata{text,538683564} \textdsversion{12} \template{default} \define{ness } \define{footnote attr:[Flags OverBar Int Set] attr:[FontSize PreviousFontSize Point -2]} \define{italics } \flushright{ \ } \center{\bold{\bigger{Building Hypertext on a Multimedia Toolkit: An Overview of Andrew Toolkit Hypermedia Facilities}} Mark Sherman\footnote{\ \begindata{fnote,538643448} \textdsversion{12} \enddata{fnote,538643448} \view{fnotev,538643448,25,0,0}This work was performed as a joint project of Carnegie Mellon University and the IBM Corporation. Some of the work was supported by the National Science Foundation under contract ASC-8617695. The views and conclusions in this document are those of the authors and should not be interpreted as representing the official policies of the IBM Corporation, the National Science Foundation or Carnegie Mellon University.} Wilfred J. Hansen Michael McInerny Tom Neuendorffer } \center{Information Technology Center Carnegie Mellon University 4910 Forbes Avenue Pittsburgh, PA 15213 USA phone: +1-412-268-6727 fax: +1-412-268-6787 email: mss+@andrew.cmu.edu } \indent{\bold{Abstract:} This paper discusses the construction and application of several hypermedia facilities within the Andrew Toolkit (ATK) and its applications. As a general-purpose, multimedia, application-development system, ATK permits many kinds of links, references and other connections to be made within pieces of content and between pieces of content, regardless of the content's medium. We argue that starting with a multimedia architecture renders trivial the construction of all forms of hypermedia. Four specific hypermedia facilities implemented with ATK are discussed: an integrated web and indexing system (Help), a simple multimedia link facility (Link), a cross reference (Textref) capability, and a link-supporting embedded object language (Ness). As a toolkit, ATK is used to build other applications which inherit ATK's hypermedia facilities. Therefore we consider briefly the way that hypermedia facilities are used in conventional applications, such as mail systems. } \indent{\bold{Keywords:} Hypermedia, Implementation, Multimedia} \begindata{bp,538342696} \enddata{bp,538342696} \view{bpv,538342696,22,0,0} \section{Introduction} Considerable effort has been devoted to cataloging dozens of different forms of links for hypertext [Meyrowitz, 1989]. Unfortunately, if one sets out to build a system incorporating each as a special case, the implementation effort becomes unwieldy before the benefits become apparent. In this paper we argue that it is preferable to begin by building a general-purpose multimedia architecture; it is then trivial to build a variety of link types. The Andrew Toolkit (ATK) [ITC, 1990; Palay, 1988] is a multimedia application development system with which system builders can create applications quickly. Its applications are in daily use by thousands of people on the CMU campus, other universities, and several industrial research laboratories. ATK is widely available on the MIT X Window System distribution. In its current release, the system provides support for many media, including multifont text, raster images, structured graphics, animations, spreadsheets, equations, and audio. The system also provides facilities for composing and connecting media, such as screen layout objects, buttons, sliders, knobs, and linking facilities of various kinds. The linking facilities provide the same service as hypertext links. The Andrew Toolkit has three features that distinguish it from hypertext systems. First, ATK is a true multimedia architecture. The presence of media other than simple text is commonplace. Second, ATK is a toolkit for building other applications. Thus, it is not a hypertext system per se. Instead, ATK allows any application built with it to use linking facilities. Third, link facilities are optional. Even in the absence of linking facilities, ATK is a fully operational multimedia authoring system, so both developers and users can ignore gratuitous linking facilities. People may choose other hypertext systems precisely because of their linking facilities, but people choose ATK for its editing and application construction capabilities, and, as an added attraction, they can utilize linking facilities as well. Therefore, ATK provides one of the few test beds for measuring the usefulness of linking empirically. In this paper, we provide some preliminary statistics of one particular use of an ATK application. \section{Multimedia Facilities} The primary composition mechanism in the Andrew Toolkit is inset nesting, as can be observed in figure 1, which shows the screen of IBM RT running three ATK applications under the X Window System. The upper-left displays \bold{console}, a system monitoring application; beneath it is \bold{typescript}, a shell interface; and to the right of both is the generic object editor, in this case editing a spreadsheet object. Within the latter, the left-side cells have been connected together to hold a multifont text object which in turn contains a raster image. The right-side cells have been grouped in three sections holding a collection of equations, an animation, and another spreadsheet object. \ The nesting of one object in another, such as a raster in the text in the spreadsheet, can continue as deeply as desired. This nesting is the central feature of ATK and is implemented as a set of protocols by which a surrounding object can completely control the environment perceived by a surrounded object. In general terms, the protocols provide that events propagate inward so the surrounding object can determine, for instance, whether or not an inner object receives mouse hits. \ The generic object editor does not understand the details of any object. If no object type is specified, a multifont text object will be used by default--many casual users rely on this default and believe the object editor to be a word processing system. Since the object editor works on any object, the same program can be used to manipulate any medium, and thus forms the basis of a multimedia application. On top of these basic facilities, one can build many different, user-level linking paradigms, such as those described in the next section. \section{Hypermedia Facilities} In this section, we discuss four kinds of linking facilities that have been implemented in ATK: an integrated web, simple links, cross references in text, and fully programmable links. \subsection{Webs (Help)} The concept of webs was made popular by Intermedia [Meyrowitz, 1986]. Webs define a collection of documents connected by references. In ATK, the impetus for developing a web subsystem was to support the Help system, which organizes and cross references help from many sources, including locally written help files and Unix manual pages. Figure 2 shows the Help program running. The main area of the window--on the left--displays one of the files of help information. The top two panes in the right column display available information, with general help on top, just above help for commonly used programs. Both panes represent precompiled collections of references and act as starting points within a web. One can dynamically put together a collection of references, as shown in the bottom-most pane in the right column. Here we show the authors' attempts to learn how to make screen snapshots for this paper. As various help information is found, bookmarks in specific documents may be added so that we can move from document to document quickly to collate the necessary information. Users can add or remove the panes in the right-hand column as desired. The precompiled lists provide starting points within a web; users navigate from document to document through the use of marked links. In figure 3, we see another help document with a link marked. When the link is followed, the new document is displayed in the main part of the help window. The system uses auxiliary files to map link-names with help documents. Different auxiliary files can be used to provide different mappings. For example, the mapping files (web) used by ATK developers contain references to local, obscure system programs while the mapping files (web) used by the main campus provide information on stable, released systems. Thus, the use of new auxiliary files allows one to create webs of information for any application, not just help files. Although users may supplement the mapping file to extend the web, they may not replace the web with one of their own. \subsection{Simple Links (Link)} \footnote{\ \begindata{texttag,538623192} \textdsversion{12} Simple Links\ \enddata{texttag,538623192} \view{texttagv,538623192,23,0,0}} The most common form of linking is a reference from one document to another. The special object (inspired by NoteCards [Halasz, 1987]) that contains a reference is called a \italic{link}. When followed, the link causes the reference to be displayed in a new window employing the generic object editor. Figure 4 shows a simple document with three links in it. One link is contained in the spreadsheet, another in the text and the third is within the drawing. As an ATK object, a link can be placed anywhere other objects may be placed. The link is followed by clicking the left mouse button on the link symbol. As a separate entity, the link object has no global knowledge about the containing document or further links in referenced documents. Therefore, there is no way to get global information about the web in which the link is embedded. The destination of a link is a filename. Since our site uses a wide area network distributed file system [Howard, 1988], links can refer to documents that exist across the country as easily as documents on the local workstation. However, moving a set of linked documents is non-trivial, since absolute pathnames are encoded in the document. \subsection{Cross References (Textref)} While simple links provide a reference from one point in a document to another file (but not within the document), cross references are used to provide references from within a document to another point in the same document. Traditionally, in printed text a cross reference appears as a label, similar to a footnote, at the target, with an indication of the target page and label at the source of the cross reference. ATK provides support for the traditional use of cross references, but, in addition, allows the user to interact with a reference when the document is on the screen. Users define \italic{tags} that denote destinations and \italic{references} that denote links. Clicking the left mouse button on a reference will make the target (tag) visible and move the text caret to the target. In figure 5, we show a document with its tags and references exposed so that the names are visible. Normally, only icons indicating tags or references would be visible. While cross references work only in text, this is not a serious limitation. Since our text object can embed other objects arbitrarily, one simply places references adjacent to non-text objects in a text object to reference other media. \subsection{Programmed Links (Ness)} The most sophisticated linking facilities in the Andrew Toolkit are provided by the embedded object language Ness [Hansen, 1990]. This is essentially an advanced Hypertalk-like language [Atkinson, 1987], where the elements are laid out utilizing the ADEW application builder [Neuendorffer, 1990]. The language can be used to extend objects in documents or to build entire applications, such as the quotation browser shown in figure 6. The main portion of the application's window is devoted to a scrollable document containing a number of quotations about birth. Across the bottom of the window are buttons which perform various operations including simple movements within the document, such as moving to the next or previous quotation. Thus these buttons are similar to the Next and Previous buttons often found in Hypercard applications. But the document is a normal text object and has all the behaviors that users have come to expect from text; they can scroll with the scrollbar and conduct normal text searches. Within each entry, a mouse click on a reference in a "CF:" line scrolls the text to display the referenced message. For example, figure 7 shows the text scrolled to the appropriate reference after a click on "Macbeth." The linking performed by the embedded language is simple and quite general. If desired, one can use the full facility of an object-oriented, multimedia manipulation language. For example, one can move within a document, move to another document, move to multiple documents in multiple windows, and search and link based on media type and content. With a full programming language, many tricks are possible; the births cross referencing is constructed with a routine in Ness which checks each mouse click to see if it is in a line beginning with "CF:". \ \subsection{Documents with a Variety of Link Types} The linking facilities we have discussed are not mutually exclusive. For example, a document within the Help system can provide simple links to other documents. The link facility itself is documented this way. Figure 8 shows the Help system in the top window displaying the documentation for the link object, which contains a link to supplemental materials which have been brought up in the bottom window. Another example is shown in figure 9, which shows a database of hypermedia and hypertext articles. There are programmed links that connect together pieces of information, supplemented by simple links that point to other collections of information. \section{Hypermedia Applications} All applications built with the Andrew Toolkit can utilize the above link facilities. To get a feeling for how these features are used, we consider briefly two applications that are in general use: the Help system and the Messages system. As used on the CMU campus, the Help system [Langston 1988; Ogura, 1989] provides help on all aspects of the computing environment, not just the Andrew system or programs on high-function workstations. Because users requesting help from low-function workstations (IBM PCs and Macintoshes) and terminals would not have access to the multimedia features of the Andrew Toolkit, the generally available help documentation does not contain multimedia information. The exceptions are documentation used only by the developers, such as the link documentation illustrated in figure 8. Of the approximately 200 documentation files written by our organization, there are over 3000 cross references and over 600 mappings between cross references and documentation files. Since these files occupy about 1.8 megabytes of space, there is a reference for every 300 characters, or about 5 lines of documentation. In addition, the system automatically links together general documentation and Unix manual pages. The Help system was designed, and the documentation was written, with links in mind, so the prevalence of references is not surprising. However, the message system built atop ATK [Borenstein, 1988] had no a priori design for hypertext information. Indeed, the overwhelming majority of the 2400 bulletin boards it offers are generated by non-ATK sources, and hence do not exploit any multimedia or linking facilities. Fortunately, the private bulletin board used by our organization of 30 researchers consists of posts made almost entirely by an ATK program. Because members of our organization have both the knowledge of how to use the linking features of ATK and access to ATK-based message creation programs, we have an opportunity to examine the prevalence of linking. Over the last two months, 369 messages were posted on our private bulletin board. Of those posted, 290 messages had some multimedia feature in them. The most popular feature was multifont text--258 or 88% of the multimedia messages used only that feature. However, of the 32 multimedia messages that used more than multifont text, 22 contained some linking feature. While not an overwhelming endorsement of hypertext or hypermedia, a 6% casual usage rate indicates some appreciation for linking. \section{Conclusions} The Andrew Toolkit effort began not as a hypertext effort, but as a general architecture for multimedia documents and applications. The design was intended to provide for incorporation of a variety of sorts of applications within documents or within each other. We have shown in this paper, however, that the resulting system is an excellent medium for hypertext and hypermedia, providing many forms of links with very little implementation effort for any one. Several linking styles have already been utilized in ATK applications. Web-based linking was chosen for an application--the Help system--which contains a lot of slowly changing information organized ahead of time. Simple links and cross references are used for casual references, as might appear on a bulletin board, while computed links are used for database-like applications. There does not appear to be a universal choice for a linking mechanism, and, even within the Andrew Toolkit, other choices are possible. For example, a group at Olivetti has independently developed a hypermedia system on top of the Andrew Toolkit [Olivetti, undated]. We believe that our investigations indicate that one should not concentrate one's efforts on a single linking system or on trying to extend a simple hypertext system into a hypermedia system. A better path is to investigate different linking mechanisms within a general-purpose multimedia system. By this path, we may find the best ways that linking can be used and add linking as another tool in our arsenal for organizing information. \section{References} \description{ [Atkinson, 1987] Atkinson, B., \italic{HyperCard}, Version 1.0.1, M0556 / 690-5181-A, Apple Computer (Cupertino, CA, 1987). [Borenstein, 1988] Borenstein, Nathaniel, Craig Everhart, Jonathan Rosenberg, Adam Stoller, "A Multi-media Message System for Andrew", \italic{Proceedings of the USENIX Winter Conference}, Dallas, (February, 1988), 9-21. [Halasz, 1987] Halasz, Frank G., "Reflections on Notecards: Seven Issues for the Next Generation of Hypermedia Systems," \italic{Hypertext '87 Proceedings,} Nov. 13-15, 1987, Chapel Hill, NC, pp. 345-365. [Hansen, 1990] Hansen, Wilfred J., "Enhancing documents with embedded programs: How \ness{Ness} extends insets in the Andrew Toolkit," \italic{Proceedings of 1990 International Conference on Computer Languages}, March 12-15, 1990, New Orleans, IEEE Computer Society Press (Los Alamitos, CA, 1990), 23-32. [Howard, 1988] Howard, John. H., "An Overview of yhe Andrew File System," \italic{Proceedings of the USENIX Winter Conference}, Dallas, (February, 1988). [ITC, 1990] \italic{Andrew Toolkit Programmer's Manual}, Information Technology Center, Carnegie Mellon University, Pittsburgh, PA. 15213, USA, January 1990. [Langston, 1988] Langston, Diane, "Background and Initial Problems for the Andrew Help System," \italics{Proceedings of the 35th ITCC,} Society for Technical Communications, 1988, p. ATA-47--ATA-50. [Meyrowitz, 1986] Meyrowitz, N., "Intermedia: The Architecture and Construction of an Object-Oriented Hypermedia System and Applications Framework", \italic{OOPSLA '89 Proceedings}, Portland, OR, 1986. [Meyrowitz, 1989] Meyrowitz, N., "Hypertext--Does it Reduce Cholesterol, too?", presented at Hypertext '89, Pittsburgh, PA, November, 1989, IRIS Technical Report 89-9, Brown University (Providence, RI, 1989). [Neuendorffer, 1990] Neuendorffer, Thomas P., "The Andrew Development Environment Workbench: An Overview", \italic{The Andrew Project}, Technical Report, Information Technology Center, Carnegie Mellon University, 4910 Forbes Ave., Pittsburgh, PA. 15213, 1990. [Ogura, 1989] Ogura, Ayami, Jennifer Robertson, "Designing Hypermedia Help Systems: Problems and Issues", \italic{Conference Proceedings, \italic{SIG}}\italic{DOC 89}, Pittsburgh, PA, November 8-10, 1989, p. 5-12. [Olivetti, undated] "Hypermedia Help System", Olivetti Internal Memo, Olivetti Pisa Research Center, undated. [Palay, 1988] Palay, A. J., W. J. Hansen, M. Sherman, M. Wadlow, T. Neuendorffer, Z. Stern, M. Bader, and T. Peters, "The Andrew Toolkit - An Overview", \italic{Proceedings of the USENIX Winter Conference}, Dallas, (February, 1988), 9-21. }\ \begindata{bp,538620520} \enddata{bp,538620520} \view{bpv,538620520,24,0,0} \indexi{Help: at least 3078 cross references, 196 files, \ 615 mappings 7 multimedia refs in help files } Inserted fig. 5: example of cross references.\ \enddata{text,538683564}