Using a cooperative hypermedia editing tool to enhance group communication and productivity

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Using a cooperative hypermedia editing tool to enhance group communication and productivity

Adelino Santos

Fraunhofer Institute for Computer Graphics, Wilhelminenstrasse 7, 64283 Darmstadt, Germany e-mail: [email protected]

Cooperative hypermedia means product- ing and manipulating hyperorganized multimedia data by a group of (co-)users. We have been realizing a prototype that enables coauthors to cooperatively produce hypermedia documents. It ~llows co- authors to communicate their ideas, drafts, guidelines, and constraints within a group in order to exchange information (remote- ly or face-to-face) and improve the final document, When analyzing the transition from individual work to group work within different human activities, two pitfalls are often detected if computer support is considered. On the one hand are the social and technological communication problems, particularly if members of the group are geographically distant from one another. On the other hand are the productivity falls, which are usually due to communication difficulties and frequent social inadequacies of the group's computer support. We would like to propose the use of this prototype - CoMEdiA - as a way to enhance, or prevent the fall of, intra-group communication and the outcomes of group edit tasks (constrained to the kind of tasks for which it has been designed). Most of the techniques used to achieve this can be used in other tools to support other specific type of group activities.

Key words: Multimedia - Cooperative editing - Multi-user interfaces - Hyper- media

1 Introduction CoMEdiA C[Co_operative hyperMedia Editing Ar- chitecture (Santos 1992a)] is an editor to support cooperation among several authors, multimedia editing, and functionalities for the non-sequential organization of files. The most important concepts are the communication styles (synchronous, asynchronous, and off-document), hyperorganization, multimedia integration, public comments, private annotations, selective telepointing, multi-user interface, social role (chairperson, author, commenter, and reader), access techniques (chunk and position), co-authors' identification, and WYSIWIS (What-You-See-Is-What-_I-_See). CoMEdiA is designed to support small groups of two to six co- authors - working in possibly different locations (connected over a local area network, LAN) - who want to collaborate (not compete) in order to produce a final document. We assume that each co- author works towards a goal of common interest, supports the other co-authors, and promotes the progress of the group. Examples of multimedia documents (demanding people with different back- grounds) to be produced this way are scientific re- ports, newspaper articles, project proposals, source-code documentation, publicity rendering scenes, animation scripts, or object-modeling sug- gestions (Santos 1992b). Our main motivation for this work are the problems that arise with the transition from individual to group work, involving different human activities. On the one hand are the social and technological communication problems, particularly if members of the group are geographically distant from one another. On the other hand are the productivity falls, which are usually due to communication difficulties and frequent social inadequacies of the group's computer support. Multimedia techniques enable the production of non-traditional documents containing enormous amounts of information. How a group can properly produce such information and communicate about it without en- countering the above problems are questions to be tackled. An integrated use of several communication media, such as video, audio, text, brainstorming graphics, or animation simulations is necessary to achieve a higher index of user participa- tion and a broader information bandwidth. To mention one example, a significant portion of time spent in organization is spent working or trying to work in group. Estimates range from 60 to 70% for managers, according to American publications. Studies indicate that office workers can spend up to 70% of their time in meetings. A recent German

The Visual Computer (1993) 10:3445 @) Springer-Verlag 1993

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study determined that managers spend 40% of their 59-hour work week on communication. The detailed analysis yielded the following results:

Work activity type Time Work activity type Time (%) (%)

Classic informal 19 Classic official 8 meetings meetings

Telephone 13 Incoming mail 8 Reading documents 11 Outgoing mail 7 Preparing documents 11 Other activities 23

We can see here that much time is spend in produc- ing information individually or within a group. In fact, 18% of the time (preparing documents and outgoing mail) directly relates to document production and 26% of the time (classic informal and official meetings) directly to group work and indi- rectly to document production. Other than meetings themselves, a large amount of time is spent on communication in a variety of forms. The majority of this communication is used for coordinat- ing people working together trying to accomplish goals they could not accomplish alone. Thus, the time spent in group work makes the issue of improving group effectiveness (for example, through computer-supported cooperation) a key one. We think this paper approaches the solution of this problem and brings something new to the field of cooperative editing, because the prototype we have been building combines various features that were formerly only present in different systems. There- fore, an integrative characteristic was missing (San- tos 1992a). We bring to discussion a way of representing and integrating the cooperation and organization aspects of multimedia documents. The multimedia documents can be non-sequential and multimedia technology is also used for communication purposes. Co-authors can use text, graphics, and audio (voice) to communicate and brainstorm.

1.1 Rationale

Nowadays, hypermedia processing is a topic studied by numerous researchers. The same is true for computer-supported cooperative work (CSCW), which brings new potentialities to computer science in general. In this work, we have been explor-

ing the promising advantages of merging these fields. There are a number of different approaches to developing cooperative multimedia editing systems. One way is to modify existing single-user, single- medium systems. This has the advantage of pro- ducing quick results, and users may already be fa- miliar with such systems, facilitating their adapta- tion to the new system. However, it is difficult to find a set of single-user tools that is broadly ac- cepted. Usually, appropriate cooperation and communication mechanisms are not supported. The multi-user interface and media integration gener- ates another bundle of problems. We adopted another approach. Namely, we have been studying and combining state-of-the-art research on social aspects of cooperation, i.e., the effects of task divisibility and communication mo- dality on work process, group performance, and individual experiences (Galegher and Kraut 1990); features for view-sharing software that must be considered during design and evaluation phases (Greenberg 1990), a series of issues in cooperative text editing (Olson et al. 1990), overall collection and survey (Greenberg 1991a), observation of a group of designers communicating over face-to- face, video, and telephone (Bly 1988), theoretical issues on design as a cooperative activity (Bodker et al 1988). Also, concepts of hypertext and hypermedia have been revised: in Akscyn et al. 1988; KMS, a distributed hypermedia system for knowledge managing; in Catlin et al. 1989, InterNode, a hypermedia system to support annotative collaboration; in Conklin and Begeman (1988), gIBIS, a hypertext tool for complex problems and early design delib- erations; and in Goodlet and Pemberton 1990, Writer's Assistant; a hypertext tool for design. We also have been studying notions of multi-user interfaces (Wulff et al. 1990, Neuwirth et al. 1990, Biel 1991, Olson et al. 1990). For existing prototypes, in which cooperation is the central notion, see Sect. 3 as well as Lai and Malone 1988 for ObjectsLens, a spreadsheet for cooperative work; Stefik et al. 1988 for CoLab, a shared workspace for face-to-face meetings, Greenberg and Bohnet 1991 for GroupSketch, a multi-user sketchpad; Whittaker et al. 1991 for an evaluation of mediated remote communication using a shared whiteboard with and without speech; Bridwell-Bowles et al. 1987 for an analysis of cooperative writing; and Galegher 1990 and Aceves et al. 1988.

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2 Results achieved

One of the difficulties in building cooperative multimedia editing tools is that it raises diverse problems on distributed systems, multi-user interfaces, media integration, hyper organization, communication, psychology, and human factors. We intended to realize a system that would diminish the costs and restrictions associated with face- to-face communicat ion and the demand for synchronous availability (Galegher 1990). Due to the three communicat ion modalities supported (synchronous, asynchronous, and off-document), this system allows the information-exchange capacity that other cooperative editors (e.g., DistEdit and Quilt - see Sect. 3) and computer-mediated c o r n -

munication systems (e-mail and tele-conferencing) lack. It enables co-authors to work in the same room (face-to-face) or in remote locations within a LAN. The algorithm used to support cooperation in CoMEdiA (Ordering Algorithm; see Hornung and Santos 1991) has its origins in distributed operating systems (Lamport 1978, Ricart and Agrawala 1991). Briefly, referring to its properties, we can say it implements a mechanism of logical time stamps and a total order to enforce a negotiation between the processes of each co-author to solve conflicts in the accesses to a multimedia document (they come to an agreement about which access should be made first and how to store the waiting ones). It guarantees mutual exclusion (just one co-

iCase-~tud~: CooperetiveMultimedia Editing

For this cese-stt~5~ we will use a prototype tool for cooperat: i multimedia editin 9, namel~ a cooperative ~ulti~edia editor cal CoMEdiA - Coooerative h~perMedie Editin9 Architecture.

This edito~ support~ cooperation amon9 'several co-a~thors, multimedia doou~lent editln9, multimedia co~un%ca~ion, and ~unctionalities Cot the non-sequential organization o~ ~i]es.

]'he ~w)st importaF, t concepts are: ~itimedie data inte9ration (Text, Static Images, 2D-graphics. coopBration :upport;h~jper organization;private annotations an( selective tele-pointing, users" identification (multi-cuesorsl acces~ techniques (ChuNx and Position)'communication styles (! social roles (s ~tho~, ~reta~-W, Com.~-~-~t~ and R~ eoop~ration t~l~es (I~'ainstorm, Shared and Editoe)'multi-user :

Mere we istend to ire~stigate if it is possible to describe t| use of" CoMs b~ ~e~ of the S-~del.

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Fig. 1. CoMEdiA environment. A multimedia document with four chapters, three of which are activated at the moment. One chapter containing text and another containing static images are visible

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l.omputcr author accesses a document position or chunk at a time) and serialization (if co-author X performs the editing action x in the document before co-author Y performs action y then, independently of the network delays, action x will be effective before action y) in these accesses. It prevents deadlocks (every co-author process would be infinitely waiting for another co-author process to do something; no editing action by any co-author would ever be effective) and starvation (one co-author process would always be pre-empted in the accesses, pre- venting its editing action to become effective) or any of the co-author processes, the fairness proper- ty (no co-author process has more priority than the others) is respected, and global consistency (the versions that the several co-authors see and process are coincident) of the document is maintained. The CoMEdiA environment (Fig. 1) shows a cooperative editing session in which the multimedia document being processed by the group has four chapters (one with text, one with 2 D graphics, and two with static-images). The organization of the multimedia document is shown (upper left) as well as the multimedia library and the multimedia document windows. The former is a library of media from which the co-authors can choose the medium (text, pixel images, 2D graphics, audio, and video are available) for one more chapter of document they want to create. After choosing the medium, they place the new chapter in the multimedia document window and make the connections that relate (connect) this new chapter with the rest of the document. After these steps, one more chapter of the document exists (although empty) and for editing purposes it must be activated (by clicking in icon). F rom here, we see that a multimedia document in CoMEdiA is not a sequential bundle of media pieces, but rather a hyperorganized composite of chapters (each containing one medium). Chapters containing text static images are activated (have a frame around the icon) and can be seen in Fig. 1. The chapter containing 2 D graphics is also activated, but just part of the interface is seen. Here, the co-author is currently creating a public comment in the chapter with a static image.

public comments, telepointing, multicursors, intra- group communication, and social roles. Every following paragraph will end with a list of the available options. Due to space reasons, we do not fully explain these options. Nevertheless, in the majority of the cases the names are self-explanatory.

2.1.1 Private annotations and public comments

A private annotat ion is an information fragment that refers to a certain spot in the document and expresses an idea about this spot. In the current version, it is a piece of text to be displayed in a separate window. Functioning is based on a hypermedia paradigm - it can be accessed following a link and there is an icon in the margin of the document to mark its presence. It is private in the sense that each co-author maintains his/her own pieces of information that refer to a certain spot in the document. An annotat ion has a key (given in the creation), which is displayed together with the annotat ion and can be used for searching. Each annotation can be turned into a public comment. An annotat ion can contain text or graphic information. It contains a minieditor with a set of reduced functionalities. Annotat ions are appropriate to pri- vately generate ideas connected to the ones expressed in a chapter and then later communicate then to the group. This export action can be rea- lized either by making the annotations public or by means of intra-group communicat ion mechanisms. Options are the NEW (create a private annotation), OPEN (open a previously created private annotation), KILL (destroy a private annotation), PRINT (print a private annotation), SEARCH (given a key, find the annotations with that key), and M A K E PUBLIC (transform a private annotat ion into a public comment), shown in Fig.2. A public comment is like a private annotation, ex- cept that the knowledge expressed is common to the whole group. It is used to explicitly and quickly transmit information to the group (see Fig. 2).

2.1 Cooperation and intra-group communication features

Here we describe the features that support co-author cooperation, namely private annotations,

2.1.2 Tele-pointing, multi-cursors and follow co-author

A tele-pointer is a means of directing the attention of the group to a particular document location.

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Fig. 2. Two public comments made to two spots in a picture. One contains text data and the other graphics. The private annotations have a very similar user-interface

The tele-pointer in CoMEdiA is the logo (Fig. 1 top-left corner of the chapter windows), which must be picked and released. When a co-author points to something, the co-authors that are receiving the telepointing are forced to stop what they are doing and passively follow. During the telepointing process, the co-authors who do not point are frozen and just watch (this is a quite restrictive telepointing policy). To improve the functionality, there is a selection mechanism to specify from whom a co- author can receive telepointing (selective telepointing) and to whom she/he can point. A co-author can choose the co-authors that can point to her/ him in the so-called TO_ME menu, and the co- authors that she/he can point in the FROM_ME menue. In this way, co-author X receives telepointing from co-author Y only if X is in the FROM_ ME list of Y and Y is in the TO_ME list of X. In the login of a session, each co-author chooses a different cursor symbol (Fig. 3). The selected cursor is continuously shown to the other co-authors so then are aware of what is being done by all the members of the group (only the cursors that fall in the same screen are drawn, i.e., the ones that are visible for that co-author). As this can lead to overinformation, there is a mechanism to express which co-authors' cursors can be seen. Here there is one option: CURSORS (pulldown menu with the group members; only the cursors of the marked ones are visible). A co-author can follow another co-author's editing. The editors' screens become exactly the same

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(one of the co-authors being completely passive). Social roles can be used to control who can follow whom. Options are BEGIN FOLLOW, END FOLLOW, and PREVENT FOLLOW.

2.1.3 Intra-group communication

Four kinds of communication are provided: synchronous, asynchronous, off-document, and general co-authors' information communication. Among the several definitions for (a)synchronous communication, we adopt the following: synchronous communication implies communication of all group members at the same time and asynchronous communication enables participants to communicate without implying communication of all group members at the same time (Lubich and Plattner 1990). In CoMEdiA, co-authors can manipulate objects and see in real time the manipulations performed by other co-authors (WYSIWIS - see Stefik et al. 1988). Thus, synchronous communication is provided by the editing per see (each co-author is aware of all the others). Asynchronous communication - allowed in the sense that co-authors can work independently of each other's presence in the editing session - is provided in two ways. One is by the changes they allow in the document (they can be seen later by another co-author transmitting information) both as contents and as public comments. The second is by leaving messages in the

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Fig. 3. On the !eft, the login window. Here the co-author must give the group identification and additional data about herself. She chooses the access type, social role, and own cursor. On the right, the information window of a co-author

off-document communication window (in this case it works like an e-mail system). Off-document communication allows communication about the editing task (discussing plans or concepts about the document, means of drawing a me- chanical part, or writing a sentence), about the document (discussing ideas or formats), and about matters outside of the editing context (shall we play squash this evening?). The communication can be written or spoken. We want to provide the advantages of both, so that a quick, user-friendly, non- ephemeral, and safe channel is provided. This written channel is implemented using a window with an area to read and another to write (Fig. 4). The spoken channel has no particuIar user-interface. In Fig. 4, we show the channels window, which is used to open/close a communication channel between two co-authors. CoMEdiA can show diverse information about the co-authors, namely name, personal data, cursor used, login time, actual editing position, and social role (see Fig. 3). This information is displayed in a special window whenever the co-author selects the option Co-authors' information in the Cooper- ate menu or in the login window (see Figs. 1, 3).

2.1.4 Access techniques and social roles

We define two different kinds of access techniques (lock mechanisms): chunk lock and position lock. In the login window (see Fig. 3), the co-author chooses one of them and if it is not the one being used by the rest of the group then unanimity must be reached. Using chunk lock, the co-author re- quests chunks of the document for his or her own use. In this way, during the editing, there are operation cycles over chunks: Select - Ask - Edit - Free. This is cumbersome, because it requires too many actions. Using position lock, the co-author locks the position where (s)he is editing. Rarely is a group a set of equally qualified people, people with equal rights and ambitions inside the group, or people who know each other. Therefore, several kinds of problems can arise, and one re- sponse to these is the definition of social roles. This reduces coordination problems by specifying proper behaviors (responsibilities, permissible actions, restrictions, and patterns of interaction) of the group members. Social roles implemented in CoMEdiA (see Fig. 3) are chairperson - chairs an editing session; author - one of the participants

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Fig. 4. Off-document communication and channels windows�9 The channels window is used to establish a communication link (written or spoken) between two users. The off- document communication window is used for the written communication

in the meeting who actively contributes to produc- ing the document; commenter - only has rights to comment on the authors' writings; and reader - only has rights to read multimedia documents. The social role of each of the participants in a meeting is defined in the login and not all the roles available must be used. There can only be one chairperson (the first to choose this role in the login), but the other categories have restrictions or numbers. Following is a list with examples of co- authors ' actions within an editing session: (1) intra- group communicat ion facilities, (2) private annotations, (3) public comment, (4) multimedia editing functionalities, (5) individual and global information, (6) change other co-author's social role, (7) edit parameters (text position lock, cursor color), (8) disable the login of a co-author, (9) manipulate multimedia documents (as a whole). We now specify which of these actions can be un- dertaken by each social role: cha i rperson- all, author - 1, 2, 3, 4, 5; commenter - 1, 2, 3; reader - 1 , 2 .

2.2 Multimedia features

In the present version, the media available are text, static pixel raster images, 2D graphics, and audio. The usual file managing functionalities are available for these media. For the text medium, commands such as UNDO, COPY, PASTE, CUT, and SEARCH & SUBSTI-

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TUTE, implement customary edit functionalities. For pixel-raster images editing, several drawing functionalities are available (over a loaded image in background or over white paper): LINE, REC- TANGLE, OPENPOLYGON, CLOSEPOLY- GON, CIRCLE, ELLIPSE, F R E E H A N D , TEXT, ARC, and PIE. As general functionalities, we have ZOOM, DELETEALL, COPYAREA, PAS- TEAREA, CUTAREA, FILLAREA, and menus to choose the pattern of the fill area, line thickness, and line type (see Fig. 1). For 2 D graphics editing, there are various drawing functionalities (over a loaded image in background or over white paper): LINE, RECTANGLE, OPENPOLYGON, CLOSEPOLYGON, CIR- CLE, ELIPSE, TEXT, ARC, PIE. As general functionalities we have SCALE, DRAG, DELE- TEALL, COPYAREA, PASTEAREA, CUT- AREA, COPYPRIMITIVE, PASTEPRIMITIVE, CUTPRIMITIVE, F ILLAREA, GROUP, UN- GROUP, and menus to choose the pattern of the fill area, line thickness, and line type (see Fig. 1). It is possible for the co-authors to communicate using voice. Through a microphone and a loud- speaker at each workplace, after clicking the appropriate icon there is direct connection (telephone- like) between the co-authors (see Fig. 4). Neverthe- less, we still have some synchronization and hard- ware problems, because we are trying to achieve reasonable quality at low cost. We have been realizing everything by software (voice capturing,

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compressing, transmission, decompression, and play) using only Ethernet and TCP/IP as network support. We intend, in the near future, to use ISDN or FDDI (see study of possibilities in Jfiger and Tritsch 1992). In order not to overload the network, we introduce a level filter so that only voice over a certain level, but not background noise, is transmitted. We have been testing the size of the packets to transmit and the type of sockets; we send 1/8-sec packets and use D A T A G R A M sockets. We are now working on integrating audio as an additional documents media. We began with the text medium and continued with static pixel-raster images and 2D graphics due to the (growing) processing complexity of the media. We will go on in this way and later integrate video both as a communication medium and as one more medium belonging to documents.

2.3 Hyperorganization features

The central notion of any non-flat organization - hyperlink - is supported by CoMEdiA. Each hyperlink has an arbitrary (sensitive) zone as origin, an arbitrary location in the document as target, a key, and a label. The key represents a layer to which the link belongs. The only semantic function of these layers is that a net of nodes connected by links can be formed and manipulated with the same key. Thus, there is an overall net of links and nodes and also all the sub-nets the co-author forms using the keys. This allows not only the non- sequential organization of a document, but also the simultaneous presence of other organization methods. The label is just a comment to the link to be displayed when the link is navigated or back- navigated.

3 Other approaches and related work

Different approaches have been taken to the problems of cooperative multimedia editing, and several prototypes have been built. ShrEdit (ShrEdit 1990) allows users to edit simulta- neously a text file having true concurrent access. The changes are reflected for all and there is an insert position lock mechanism. It minimizes un- necessary lock conflicts by minimizing the access units. It provides neither private annotations nor

multimedia capacities and there is no users' identification (e.g., the position of the co-authors' editing operations is not shown). The user can park him/ herself, being just a watcher then. Quilt (Leland et al. 1988, Fish et al. 1988) is a collaborative document-production system based on observational studies of writers. It concentrates on user communication and annotation and provides revision suggestion, messaging, and notification facilities. It combines concepts of social aspects of the writing task, hypertext, and direct-manipula- tion interfaces. It provides social roles (co-author, commenter, and reader) and cooperation types (shared, exclusive, and editor). The user can custo- mize the document definitions, annotations, social role, and access permissions. PREP (Neuwirth et al. 1990) focuses on enhancing the effectiveness of loosely coupled collaboration. It uses organizational techniques other than the usual text editors, with great emphasis on hypermedia techniques (see Sect. 1.1). It allows users to create chunks that correspond to ideas (containing text, grids, trees, and images) and links connecting the chunks so the user can build networks of ideas. To support collaboration, the system allows the creation of related columns of chunks. One column can form the contents of a paper and another the paper plan. Comments can be added in another column as well as annotations and notes. It supports social roles (co-author, commenter, and reader), comments, and communication about plans. DistEdit (Knister and Prakash 1990) is a toolkit that can be used to build cooperative editors out of traditional single-user editors. Although the sense of the word cooperative is limited here, Dist Edit still presents some good features. Almost any single-user editor can be easily transformed in order to support collaboration. It supports the use of different editors within the same editing group, so the users do not need to get used to a new application in order to collaborate, because all the functionalities and interface mechanisms are maintained. It provides two social roles (master and ob- server) although only the master role has editing capacities and there can be only one master at a time. There is neither multi-user interface nor asynchronous communication. ICICLE (Brothers and Sembugamoorthy 1990) is intended to augment the efficiency of formal code inspection. It supports knowledge-based analysis of the source code, margin annotations, coopera-

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tive discussion, and comments during inspection meetings. It implements social roles (moderator, reader, scribe, author, and inspector), telepointing, and relaxed WYSIWIS. It is not to be used re- motely. Aspects (Biel 1991) combines text, graphics, and pixel images in a joint editor. As in DistEdit, a scheme for combining and augmenting single-user, single-medium applications was used. The user can create documents or use ones already created by other single-medium, single-user applications. It has the advantage that users do not need to get used to a new application in order to collaborate. It supports WYSIWIS and there is one cursor for each user (but no other form of user identification). It provides roles (master and participant) and cooperation types (free-for-all, medium, and full me- diations).

4 Analysis and comparison of features

People who participate in group editing have a cognitive architecture that has well-known characteris- tics. Perception is excellent; short-term memory is flexible and rich, but slow and inaccurate; and learning is powerful, but similarly slow (Olson et al. 1990). It is also known that user-system and user- user communications have a key importance in cooperation, namely for coordination support (Leplat 1991). CoMEdiA's user interface has several aspects determined by the muli-user nature. It gives a global perception of the cooperative process and document state. It gives constant visual signs to show the state of the cooperation - a hand-up bitmap to show that someone is asking access to a chunk; one cursor for each co-author and one extra for telepointing; possibility of identifying co-authors who are in an editing session and what they are doing; different bitmaps to express which windows have public and private information. In this section, we will make frequent references to Sects. 2 and 3 for comparison purposes. The structure of this section is identical to that of Sect. 2 for ease of reading and analysis.

4.1 Cooperation and intra-group communication features

4.1.1 Private annotations and public comments

Annotat ions are, as in traditional editing, a practical means for capturing ideas and facts. On the other hand, al though the addition of a message could be helpful (capturing an idea before it is for- gotten), having it immediately public can bring un- necessary reactions and criticisms. Consequently, the ability to express an idea in private is a necessary feature. Quilt, PREP, and ICICLE support private annotations. Comments are a means of supporting one of the most common events in a co-authoring relation- ship, i.e., the edit-review-incorporate cycle (an author gives draft to another person, who revises it and returns; to the first author, who incorporates the new material). PREP includes rather complex comment features, whereas Quilt (revision suggestion) and ICICLE present simple comment features.

4.1.2 Tele-pointing, multi-cursors, and follow co-author

It is useful to be able to direct the attention of co-authors to a particular location within the display (as happens in any face-to-face meeting). In CoMEdiA, as there is no mechanism to impose behavior rules on the use of the telepointer, nothing can prevent a co-author from using it too much and thus become annoying to the others. In this case, the only thing that could be done would be to disable the telepointer. However, this would prevent a co-author from receiving any telepointing from any other co-authors. In CoMEdiA, each co- author can express to whom and from whom the telepointer works. In the future, when we add audio and video, they will be included in the off-document communication, which will overcome some of these problems. Only ICICLE includes a telepointing mechanism, only Aspects has multicursors, and no system has the follow co-author feature. Particularly, when editing hypermedia documents problems related to the location of a user in the navigation process (known as the lost-in-the- hyperspace syndrome) and location of other co- authors can occur. Such problems can be overcome by these two features.

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4.1.3 Intra-group communication

It is very important to have WYSIWIS, otherwise problems can arise - e.g., members' interest for the group task or group cohesion can diminish. How- ever, the most serious problem of the lack of WY- SIWIS would be the loss of synchronous communication advantages. Nevertheless, the WYSIWIS style of CoMEdiA contrasts with the systems con- sisting of one machine, the display of which is pro- jected onto others via a facilitator (DistEdit, As- pects, or shared-windows applications). ShrEdit, DistEdit, ICICLE, and Aspects have WYSIWIS. One of the arguments against a plain synchronous- communication philosophy is when a co-author writes a paragraph or makes a public comment, points it to the others, and asks for a reply comment. If the responses are made using the same mechanisms (ordinary paragraph or public comment writing), they will be seen by all group members when just the co-author who wrote the first comment should receive them. To avoid this superfluous communication, off-document communication is very appropriate. It allows a private dialogue between just two of the co-authors. As a result, groupwise information exchange can be made using the public comment mechanism, while pairwise information exchange can be made through the off-document communication mechanisms. Asynchronous communication if useful, because it enables co-authors to work alone or in subgroups. Co-authors can communicate with others (who are not in the session) by leaving messages in public comments or using the off-document facility. The fact that a co-author can leave a message in the off-document window is a mixed form of off-document with asynchronous communication, which is not present in any other system mentioned above. The combination of these communication features contrasts CoMEdiA with other systems that just provide one of these types (Quilt, ICICLE or As- pects) or with document authoring and teleconfer- encing tools. Users' information is not present in any system mentioned in Sect. 3.1.

It can be made more co-author-friendly if the Se- lect_Chunk and Ask_Chunk operations (see Sect. 2.1.4) are put together in the same action. It is much more prone to access conflicts and has common disadvantages with the distributed file systems that cause file locking. Using position locking, co-authors have more editing freedom, but tend to overload the system more. The latter is much more user-friendly and, as long as co-authors can see where the others are located in the document, it is easy to use (a co-author can always see the cursors of the others, if she/he wants). On the other hand, it can be difficult for two co-authors to edit the same paragraph (e.g., seeing lines moving at the speed of double insertion). ShrEdit implements position lock, but no system supports both mechanisms. We adopted the social roles we consider necessary and sufficient for most of the cooperative editing meetings (chairperson, author, commenter, and reader). In spite of the advantages of social roles, we are also aware of the restrictiveness introduced by them. We refer to some problems in Sect. 5 and because of them we have planned some extensions of the concept. Quilt, PREP, DistEdit, ICICLE, and Aspects provide various forms of social roles.

4.2 Multimedia features

Experienced writers produce intermediate external representations that have no direct relation to the document. When working with environments that do not support any graphical primitives (arrows, boxes, grids, pies, etc.) to show conceptual relation- ships between ideas, co-authors report frustration and important planning activity and brainstorming is reduced (Flower et al. 1989, Bridwell et al. 1987). More than just graphics, other media (bitmaps, raster images, audio, and video) enrich the documents' contents as well as the production process. Only Aspects and PREP include multimedia features. DistEdit may eventually include them, depending on the application.

4.1.4 Access techniques and social roles

The advantage of working with chunk lock is that the co-author has the guarantee that no one will disturb his/her work during the editing process.

4.3 Hyperorganization features

To many people, professionals as well as vendors, hyperstructures have become the way to organize documents (Conklin and Begeman 1988). Due to this, it has been possible to develop, to a high de-

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gree rather advanced co-author interfaces and browsing mechanisms. In CoMEdiA the hyperstructures are rather simple compred with other systems that concentrate on them. PREP has so- phisticated hyperfeatures; ICICLE and Quilt refer to them; and ShREdit, Dist Edit, and Aspects do not have them.

5 Summary and future work

We have been comparing the editing supported by CoMEdiA with both traditional group writing and single-user computer writing. CoMEdiA multimedia features can substitute and integrate the use of different single-media applications. Annotations and comments substitute margin jottings. Synchro- nous communication and WYSIWIS intend to rep- lace face-to-face communication and version merging. Asynchronous communication is useful in the case that a co-author misses a meeting. The off- document communication feature is designed to assist the co-author with the quick exchange of ideas, planning, conceptualization, coordination, and informal side talks. CoMEdiA's selective telepointing feature substitutes the frequent action of calling the attention of whole group. Co-authors' identification and login features provide protection and authorization features. Face-to-face contact between co-authors, in which each individual's behavior is affected by the behavior of the others, is necessary. The inclusion of a video and an audio channel using an ISDN or FDDI connection is being studied. This will help in developing affective ties and enforce the synchronous-communication capacities. Enhancing the multimedia range of the documents' contents is a primary goal. First steps are already being made in integrating audio as one more medium for editing. Later, video (both as a facility for real-time communication and as one more intergrated medium for the multimedia documents) will be integrated. Brainstorming, where a group of people generate ideas in quick succession, is the classic technique for improving creative productivity through simultaneous work. For this reason, we intend to provide a brainstorming zone (with pixel graphics and no locks). It is easy to devise situations in which the social roles defined do not suffice. Moreover, we think that no multitude of predefined social roles can

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cover all cooperation situations. We want to include dynamic changing and temporary social roles. These are two notions we are working an and that will be available in the next version.

6 Conclusions

We have given reasons why we find it necessary to develop a cooperative multimedia editing tool and we have substantiated the conceptualization of such a tool. We described the system achieved, justified the options taken, and compared it with other state-of-the-art approaches. Given the moti- vations in Sect. 1, we think we have contributed to arriving at solutions. We feel this paper brings something new to the fields it touches upon: multimedia processing and cooperative editing. The prototype available has some innovative features and others that were formerly only separately present in different systems. An integrative characteristic was missing in other prototypes built to date. In the aspect of multimedia processing and integration, we bring to discussion another way of representing and editing multimedia documents (non-sequential and more flexible). Multimedia technology is also used for communication within the group, which opens new per- spectives. Although we are in the beginning and considerable amount of work needs to be done, namely towards the multimedia aspects of the system and towards an evaluation study, we have already a prototype available and the know-how necessary to treat the problems of cooperation in integrated multimedia.

Acknowledgements. I thank Prof. Encarna~o for the opportuni- ties; Dr. C. Hornung for support and incentive; and students G. Boikos, A. Marcos, O. Eichhorn, and L. Zhu for help in implementation. I also would like to thank my department colleagues, especially B. Tritsch, who has been working closely with me. Also many thanks to the members of the CO-TECH's WG3, a speiatly Erik, Roland, Erland, Thomas, Hannes, Jos6- Maria, Joze, Joroen, and Sylvia. This work as been partially funded by a CIENCIA scholarship (BD/1736/91-IA).

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A. SANTOS is responsible for the design and construction of cooperative systems, namely for multimedia document editing, in the distributed and cooperative systems department of the Fraunhofer Institute for Com- puter Graphics. He has been developing his PhD research in the area of cooperative multimedia editing. He received his degree in Computer Science from the University Nova of Lisbon and his research inter- ests include processing of multimedia documents, human-hu-

man audio and video interaction, group-work support, and ef- fectiness measurements.

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Documents

Using a cooperative hypermedia editing tool to enhance group communication and productivity