A Multimedia Enhanced CSCW Teleservice for Wide Area Cooperative Authoring of Multimedia Documents * (Position Paper) Heiko Thimm GMD – Integrated Publication and Information Systems Institute (IPSI) Dolivostr. 15, 64293 Darmstadt Germany e-mail:
[email protected] Abstract This paper presents the concept and general architecture of a multimedia enhanced CSCW teleservice that controls and monitors cooperative multiauthoring processes for possibly multimedia documents. Involved authors can be worldwide geographically dispersed. The instantiation of such a process is performed by submitting a workflow specification including multimedia directives which informally describe corresponding authoring activities. Document components completed in preceding authoring activities can be specified as activity input. The document data are fully incorporated within the workflow artifacts. The central component is a multimedia archive that provides integrated workflow- and document management functionality. A multimedia mail teleservice designed for public networks is used as communication means. Using the proposed CSCW teleservice, authoring processes can be completed in a smooth, reliable, and timely manner. Authors are relieved from tasks that bear a high potential for workflow violations and delay.
1 Introduction There is an increasing number of multimedia applications that deal with multimedia documents. The creation of such multimedia documents entails several distinctive tasks such as writing of text, drawing or scanning of pictures, creation of digital animations, digitizing of audios and videos incl. their manipulation (e.g. fading out of an audio), ... etc. Due to the different requirements these tasks impose (1) on the performing person - possibly requiring a special education or training - and (2) the local environment (special multimedia hard- and software), such documents in many application areas are completed by multiple authors. It is not an exception that these multiple authors are working on geographically (possibly worldwide) dispersed places. Furthermore, authoring processes can involve non-authors who e.g. decide about the modifications to be made before the document can be published. To our knowledge, up to know, adequate comprehensive computer-based support for this kind of multiauthoring task is still lacking. Hence, with respect to the above mentioned context, cooperating authors are faced with many administrative tasks (e.g. synchronizing the exchange of * This work is partially granted by the DeTeBerkom GmbH, Berlin, under contract number 2038/2.
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the different document parts, making document parts accessible for other authors, reminding overdue document parts, monitoring current state of completion of the document, ... etc. ) which may prevent a smooth and timely process execution. In this paper, we present a teleservice which relieves the authors from these administrative tasks and eases the cooperation between them. It allows the initiating author, who we call editor in the sequel, to define the course of the cooperation between the authors by a workflow specification. In contrast to many other workflow systems, in addition to a formal workflow description, these specifications include multimedia directives which are informal kind of messages. Hence, the resulting workflow is not exclusively based on a strict formal specification. This feature makes the overall concept more flexible and adaptable. Furthermore, this reflects the fact that the tasks to be managed are performed by humans. The view at the workflow in traditional workflow management systems is limited to the tasks to be performed. In our concept, we also deal with the realization of the dataflow between these tasks. Hence, our workflow specifications can contain the definition of input document parts that are issued together with the authoring task requests to the corresponding authors. All document parts completed in former authoring tasks of the same but also other workflows are possible input document components. This feature is especially helpful if an author has to relate to a document component completed by another author. The document components completed by the different authors are automatically ‘‘glued together’’ to one consistent multimedia document according to the initiating authors specification. Furthermore, other helpful workflow management functionality (e.g. reminding overdue document parts, maintenance of authoring process state) are provided as well. Already available infrastructure and technology is employed by the CSCW teleservice introduced in this paper. It is based on the combination of multimedia database and electronic mailing technology. The teleservice’s central component is a multimedia archive based on a DBMS. This archive provides the described workflow- and document management functionality in an integrated manner. The VODAK research prototype of an object-oriented DBMS ([11],[12]) has been applied to realize this archive. It interprets the workflow specifications submitted by editors, controls, and monitors the multiauthoring process according to the specification, and manages the storage and exchange of the document components. As communication means, the BERKOM standardized multimedia mail teleservice ([7],[13]) is employed which has been designed for public networks and which runs on a number of different platforms. In this paper, we focus on the overall concept of the CSCW teleservice and provide only little technical details. It is organized as follows. In the remainder of this section, we discuss related work. In section 2, we attempt to make clear the need for an integrated workflow- and document management approach as an adequate basis for our CSCW teleservice. Then, in section 3, we give an overview of the overall architecture of the teleservice and describe an application scenario. Section 4 provides the result of an evaluation of our concept. Open issues and the overall context of this work are discussed in our conclusion. Related Work General issues in the design of computer support for co-authoring and commenting are discussed in [14]. A concrete system that to a large extend parallels the objectives of our CSCW teleservice is the Quilt system [4] which is a collaborative tool for cooperative writing of hypertext documents. It allows collaborators to annotate work-in-progress, to exchange messages, and to track the status of the work. The authoring processes follow user-defined default style of collaboration. An electronic mail based notification system is used for the communication between the authors but not for the 2
transportation of the document data. The ‘‘assembly’’ of the hypertext document is performed by the co-authors itself and not automatically by the Quilt server. Multimedia support is limited to text and voice annotations. An example of a traditional workflow system which is targeted on business processes, as most workflow systems do, is the Echo system. In [8], the behavior of its incorporated workflow engine which is based on a generic execution model is described. Furthermore, it is shown how workflow execution can be abstracted into inter-related process objects, whose state transitions are reliably recorded, tracked, and notified to participants of the workflow processes. A workflow management approach employing event-condition-action rules on top of an active database system is reported in [2]. The realization of a workflow management system targeted on the production of a concrete scientific newspaper based on commercial products is reported in [6]. Visions, research goals, and some conceptional issues for the design of highly integrated information systems emphasizing the integration of document- and workflow management are discussed in [5].
2 Using Multimedia Archives for Cooperative Authoring In the following, we first describe the general properties of the type of asynchronous cooperative authoring we address. Then, we derive the main requirements for an adequate computer-based support system and introduce three different solutions. Finally, a comparison of these solutions is made prior before we come up with a conclusion. Properties of asynchronous cooperative authoring. The general objective is the production of a possibly multimedia document. Typically, there is one author (editor) who in the very first step makes up his mind about the requirements the document has to match. Furthermore, he determines the group of authors to be involved and which contribution they have to make i.e. which document part they have to complete as well as the input document parts they need (parts to be known in order to complete a document part). Non-authors to be involved (e.g. persons who are responsible for the correctness of the contained information) are to be considered as well. Then, the actual authoring of the document is started. Each author separately deals with his task assigned by the editor at the expected point in time and returns the completed document part. It has to be considered that authors might need to directly contact the editor or other authors. The process might also involve that the document several times has to be issued to various non-authors. Information about the document authoring process’s current state might be useful for the editor and others. Requirements for an adequate support system. Considering the properties described above, a computer-based support system should fulfil the following general requirements: (1) provision of a means to specify the desired cooperative authoring process, (2) ability to control and monitor authoring processes according to their specification, (3) facilitation of an adequate communication mechanism (incl. support for multimedia data), (4) means for the exchange and management of the possibly multimedia document parts. Note that support for the direct communication between the involved persons can also be an issue for such a support system. Three archive based solutions. One general approach towards a support system that reflects the above mentioned requirements is the employment of a workflow management archive (WFM archive) such that requirements (1) and (2) are satisfied. This means that a demanded authoring process is expressed as a workflow specification. Essentially, it defines which of the document compo3
nents are to be completed by which human author including a timing of these authoring activities. It is imagined, that such a workflow specification includes individual/personal multimedia directives (multimedia messages of type text, picture, audio, video, respectively) providing activity explanations for the authors. By submitting such a workflow specification to the archive, an authoring process is instantiated which is controlled and monitored by the archive. Requirement (3) is reflected by an incorporated proper communication mechanism. In the following, we outline three different ways how this described approach can be extended to match requirement (4). Solution 1: Workflow Management Archive with external Document Handling by Authors The document handling is simply imposed to the authors (figure 1a). Hence, the exchange of the document parts has to be coordinated and performed by the authors without any support from the WFM archive (thin solid arrows). Solution 2: Multi-Archive Solution The document handling is performed by a second archive which is a document management archive (DM archive) (figure 1b). It receives, stores, and distributes the document parts resulting from authoring activities. The operation of the DM archive is controlled by the WFM archive. Each arrival of a new document component is signalled to the WFM archive which keeps track of the authoring process state. Solution 3: Integrated Workflow and Document Management Archive In addition to workflow management functionality, the archive provides integrated functionality for the management of the multimedia documents (figure 1c). It is imagined that it even is capable of the task of ‘‘glueing’’ all document parts completed in authoring activities together to the final required multimedia document. However, this is only possible if the initiating author issues the expected document structure together with the workflow specification.
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Fig. 1: Three alternative solutions for computer supported cooperative authoring based on archives
Comparison. In solution 1, the workflow management is separated from the document management which is ‘‘manually’’ performed by the involved authors requiring some coordination. Since the documents are not accessible for the archive, they cannot be directly incorporated within the work4
flow. Instead, additional dataflow is necessary for the exchange of the document parts. Furthermore, in order to keep track of the authoring process (e.g. for monitoring timing constraints), authors must separately issue activity completion notifications to the archive. Solution 2 provides support functionality for the document management as well, relieving the authors from the need to explicitly take care of the exchange of documents. An integration of both artifacts to be exchanged, i.e. workflow data and document data, is possible requiring a tight cooperation between both archives (Figure 1b shows a solution where such a tight integration is not realized). In solution 3, there is only one archive that provides integrated functionality for both. Workflow as well as document data are interchanged in a consistent manner i.e. they are not exchanged as separate information packages. Information resulting from document management procedures can be used as feedback for the workflow management task. Thus, the state of the document authoring process can be very easily maintained. Solution 1 does not allow advanced workflow management functionality and expects form the authors numerous ‘‘manual’’ tasks such as the interchange of document parts. This can result in workflow errors and delays. In both, solution 2 and 3, more advanced workflow management functionality is possible and the authors are relieved from many of the above mentioned ‘‘manual’’ tasks. Regarding solution 2, for the authors, the employment of two separate archives can be kept transparent such that for them there might be no difference to solution 3. However, this requires a tight cooperation between both archives which can cause some communication overhead. There are database research areas (Interoperable Databases, Cooperative Information Systems) where problems related to such a cooperation and other issues are comprehensively investigated. Conclusion. The above comparison shows that using an integrated multimedia workflow and document management archive, asynchronous cooperative authoring can be properly supported. Workflow and document data are consistently handled (i.e. there is no separate data flow) and information from the document management allows to provide advanced workflow management functionality. This helps to reduce workflow errors and violations which will make the authoring process realization not only faster but also more reliable, and consistent. In the next section, we introduce a CSCW teleservice which employs such an integrated multimedia workflow and document management archive.
3 A Multimedia CSCW Teleservice In this section, we present a multimedia enhanced CSCW teleservice for wide area collaborative asynchronous authoring of multimedia documents. The teleservice is based on an archive system and electronic mail communication. It provides those integrated workflow and document management functionality that enables advanced workflows and collaboration between authors as it has been outlined in the former section as solution 3. Furthermore, it provides integrated support for direct communication between the persons involved in the cooperative authoring process. However, in the following we will focus on the specification and realization of formal workflow specifications. First, we give an overview of the architectural concept. Then, we describe an application scenario that shows its potential benefits for cooperative document authoring.
3.1 Architecture The proposed teleservice is based on an architecture comprising standalone archive clients and an archive server which provides integrated workflow and document management functionality. Ar5
chive clients access the archive server and vice versa via an extended X.400 Multimedia Mail Teleservice ([7],[13]) which has been designed for public networks. Both, workflow artifacts as well as document components and complete documents are interchanged using this mail teleservice. In the following, we detail this architectural concept which central components are shown in figure 2. The archive server is realized by using an object-oriented DBMS. Multimedia mails, multimedia documents, document parts, workflows, and activities are modeled as database objects. Functionality for workflow and document management is implemented as methods of these and other database objects. For example, there is one object that monitors the due date of authoring activities. Functionality to move the workflow forward by interpreting the workflow specification is encapsulated within the methods of the workflow and activity objects. The Archive Agent (AA) controls the processing of the database and handles the connection to the mail system for the sending and receiving of multimedia mails. On the one hand, the archive server’s operation is triggered by incoming mails. On the other, it is also triggered by the timing constraints contained in workflow specifications. Archive Client (editor environment) . workf. spec. tools
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Fig. 2: CSCW Teleservice Architecture There are three different components that constitute the archive client: (1) Workflow User Agent (WF-UA), (2) workflow specification tools that include functionality for the creation of multimedia directives, and (3) authoring tools and interfaces to such tools. (1) is for the management of author6
ing activities including communication handling. (2) is only included in the editor environment and provides means for the specification of the demanded workflow including the multimedia annotations. (3) provides means to complete requested authoring tasks. Using the multimedia mail teleservice mentioned above, workflow artifacts as well as multimedia document components (both can include multimedia data) can be exchanged between archive clients and the archive server and vice versa. This multimedia mail teleservice reflects the specific requirements of dealing with multimedia data in a networked environment by supporting in addition to the usual (i) store and forward a (ii) global reference interchange mechanism. Both mechanisms are made accessible to the server and each client by their Multimedia Mail User Agents (MMM-UA). For the store and forward, each MMM-UA is connected to a Message Transfer Agent (MTA) that follows the recommendation X.400 [3]. For the global reference mechanism, all MMM-UAs are furthermore connected to an External Reference Manager (XRM) [15]. The global reference mechanism provides a means to transmit high volume multimedia data (i.e. multimedia annotations and document components) which cannot be transmitted using store and forward for several reasons (e.g. since it may lead to congestions in MTA implementations, or it may go beyond storage capacities at the recipient’s sites, respectively). The key point of the global reference mechanism is that high volume parts of the mail to be sent are deposited on a specialized global store and a global reference (called Distinguished Object Reference (DOR) [10]) to the data is included in the mail instead of the data itself. The XRM provides the necessary services for the handling of global references. It includes functionality enabling a receiver of a mail containing global references to fetch the respective data from the global store. Different communication protocols which provide direct access to the referenced mail parts such as the non-realtime Referenced Data Transfer (RDT) [9] are supported. In case a client wants to view mail parts such as audio and video without prior local storage, a realtime protocol must be used between the storage and the client’s site. workflow definition part auth./non-auth. activity informal multime(incl. spec. of input doc. parts) dia directives
structure of document to be completed doc. components already completed by editor
number of specified activities equals at least number of lacking doc. parts formal specification
Fig. 3: General structure of a Workflow Specification Mail
3.2 Application Scenario In the following, we want to look in more details at the process of cooperative authoring employing our CSCW teleservice. This is done by discussing a realistic application scenario. First, we describe the initiation of the cooperative authoring process. Then, we go into the details of the realization of the specified workflow i.e. the workflow enaction. 7
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Fig. 4: Mails exchanged and their contents during a multiauthoring process Initiation of Cooperative Authoring. After some event has triggered the demand for the creation of a multimedia document, the editor has to get a clear idea of the document’s contents i.e. the information it should provide and how these information should be provided (i.e. by text, image, video, audio). There might be applications where this is predefined to some degree by certain rules like 8
document type definitions, or document authoring conventions, respectively. Furthermore, the initiator, already in this state, has to have a clear understanding of the authoring activities to be assigned to other authors and the order of these activities. The latter mainly depends on the input document parts required by the different authoring tasks. All this requires for the editor some knowledge about the other authors’ ability to contribute certain document parts which depends on the local environment (e.g. special multimedia hardware and software), expertise, and availability of certain information. A workflow specification mail as illustrated in figure 3 comprises information about all of the above mentioned subjects. The workflow definition part of the mail consists of a formal specification of the authoring and non-authoring activities including a specification of their respective input document parts, and timing information (i.e. order of activities). Furthermore, as attachment to the corresponding activities, it contains multimedia directives. They provide individual and informal messages for the selected authors, e.g., describing the expected contribution. For high volume directives, such as video directives, the mail includes a DOR i.e. a global reference pointing to the actual data stored on a global store. It does not include the data itself which are fetched from the global store at presentation time. As mandatory part, a workflow specification mail also provides a specification of the structure of the document to be created and possibly document parts already completed by the editor. Workflow specification mails of this type are sent to the archive of the CSCW teleservice to instantiate a cooperative authoring process. Cooperative Authoring Enaction. The cooperative authoring process as defined in the workflow specification mail is realized i.e. controlled and monitored by the integrated workflow and document management archive. It issues, in a timely manner, authoring activity request mails to the concerned authors, issues reminders if necessary, stores completed document parts, and makes a consistent multimedia document out of all document parts according to the predefined structure. Furthermore, it maintains the workflow state and provides other services which are helpful for the editor and others (e.g. document completion notification mail). Figure 4 illustrates the mail exchange and the information contained for a sample cooperative authoring process. For simplicity, it does not include non-authors that might have to give their OK to certain document parts. As shown, the participating authors are provided with input document parts completed in earlier authoring activities. For example, authoring activity request mail issued to author A4 includes the document parts already completed by authors A1 and A3 i.e. document parts 1 and 4. As the picture shows, the same author does not return the required document component within the expected time. Hence, in order to keep the overall delay as short as possible, the archive delivers a reminder mail to this author. A multimedia annotation is provided to every participating author in this example. The archive successively ‘‘assembles’’ the documents and, if defined within the workflow specification, delivers to recipients the document in its current state. In figure 4, e.g., the incomplete document in completion state 3 is delivered to the editor.
4 Discussion In this section, we discuss major issues with respect to the concept of our introduced CSCW teleservice. Role of Multimedia. We have to consider two aspects within a discussion of multimedia concerning our CSCW teleservice. First, the provided workflow and document management functionality is especially targeted on the creation of multimedia documents. Second, authoring process specifications 9
include individual multimedia directives for involved authors. In this respect, multimedia data is the means which enables an enrichment of the formal workflow for the document authoring process by helpful informal directives. It provides advantages which are lacking in many usual workflow management systems that are exclusively based on non-multimedia workflow specifications. Archive Functionality. We have attempted to elaborate the advantages of an integration of both, workflow and document management functionality, by means of an archive. For the concrete CSCW situation addressed, i.e. asynchronous collaborative multiauthoring within a possibly worldwide dispersed multimedia networked environment this is significantly beneficial. The messages exchanged contain both workflow as well as document data which is advantageous for the overall coauthoring process. This integration allows to realize high-level workflow management functionality. Primarily, this functionality deals with moving the workflow forward and distributing the necessary information by interpreting the workflow specification (workflow engine functionality). Using Multimedia Mail. Our proposed CSCW teleservice consistently employs multimedia enhanced electronic mail for the exchange of workflow as well as document data which both can include multimedia data. It is assumed that multimedia electronic mail is also employed when the involved persons need to directly communicate with each other (i.e. not involving the archive). The utilized mail system’s global reference mechanism turned out to be a conveniently applicable means for interchanging high volume data which cannot be handled by store-and-forward. While for distributed systems like, e.g., kiosk information systems, information systems for training, education, advertisement, and entertainment, the message delay inherent to asynchronous electronic mail is problematic, for our purpose it is not - there is no requirement that artifacts have to reach the dedicated receiver immediately. Electronic mail is a connectionless communication means which provides buffering capabilities. This is explicitly demanded for the purpose of our CSCW teleservice since the requirement that authors as well as the archive permanently have to be logged on cannot be matched in reality. An infrastructure for electronic mail already is worldwide available and multimedia data will be fully supported by commercial products in the future. Thus, in principle, the introduced CSCW teleservice could be easily provided to a large number of users. Using an Object-Oriented DBMS. For the realization of the described integrated workflow and document management functionality, the CSCW teleservice’s archive server must be based on a differentiated and semantically rich database model. This enables an adequate storage system for the multimedia document and workflow data. Direct storage of the multimedia data within the database, which is preferable, requires adequate multimedia datatypes or at least support of binary large objects (BLOBs) by long fields. Otherwise, only filesystem references to multimedia data can be stored in the database and policies as well as management tasks to preserve these references have to be defined. The database must be able to successively ‘‘assemble’’ the document parts to one consistent document according to the given document structure. This can be achieved by mapping the elements of the logical document structure into database instances modelling the corresponding document parts. Furthermore, it has to handle the notion of time inherent to workflow specifications. If active capabilities known from active databases such as event-condition-action rules are not supported by the DBMS, adequate other mechanisms to cope with the timing constraints have to be implemented. A very good basis for the development of a system that matches these requirements is an object-oriented DBMS like VODAK. In fact, it turned out that with VODAK’s object-oriented data definition language VML ([11],[12]) which is also a programming language, an adequate database schema can be defined. Recently, a proposal to extend VODAK’s data model by the concept of a schedule has been made [1] which can also be applied within the context of workflow management. 10
5 Conclusion We presented the concept of a CSCW teleservice that provides adequate support for the cooperation of multiple possibly geographically dispersed authors. The overall goal of this cooperative authoring work is the creation of multimedia documents. Cooperation within this context is advantageous since it encourages that the different components of a required multimedia document are completed by the most adequate authors. We regard those as most adequate authors who have (i) the expertise required to deliver the information in the necessary form, (ii) access to the necessary information sources, and (iii) the necessary multimedia equipment and the knowledge of their handling required for the creation of the document component. Using our CSCW teleservice, authoring processes can be completed in an accurate, reliable, and timely manner. The CSCW teleservice is based on an integrated workflow and document management archive which facilitates high level workflow management functionality. Authors are relieved from many administrative tasks which are automatically performed by the archive. The delivery of document data to other participants possibly over large distances employing the incorporated mail system is coordinated. Besides its support of multimedia data with respect to the document to be created, our teleservice supports multimedia directives as parts of authoring process specifications. This feature, which allows for the editor to deliver informal kind of messages to the respective authors makes our teleservice more flexible and adaptable than most other workflow management systems. A good example of an application of the suggested teleservice is the cooperative authoring of documents for a multimedia calendar of events. Raw data about the event like date, city, location, entrance fee, ... etc. might come from the editor while other parts like a video clip about the performing actor, an audio sample, a picture of the location, an image of the relevant city map, scanned newspaper reports, etc... might be contributed by different other people like e.g. photo or actors agencies, music studios, magazines, ... etc. Furthermore, in this example, several non-authors can be imagined, e.g. one who has to check that the information of the document do not violate copy-right restrictions. Other possible multimedia applications are the coauthoring of calls for papers, product announcements and advertisement, electronic newspapers and magazines, and many more. Possibly, some future version of the described CSCW teleservice will be used for the production of our institute’s own electronic multimedia newspaper [16]. Currently, in our concept, the structure of the final document is fixed by the initiator i.e. at the very first step of the authoring process. We think that by allowing, e.g., document extensions and possibly modifications in succeeding authoring tasks, an authoring flexibility helpful in many applications can be provided. Furthermore, the concept need to be extended in order to support the redoing or modification of already completed document parts (i.e. a concept for document revision control has to be integrated). This requires for the archive the ability to handle dynamic workflow modifications as well as some document versioning functionality. Another reasonable enhancement is that instead of requiring from the editor an explicit definition of the authors, the database is determining the most adequate ones. Hence, additionally the database of the archive server need to include comprehensive information about authors. It can be imagined that this information is directly provided and maintained by the authors themself. Currently, it is an open issue how we can enable the document exchange between different authoring processes such that a document component completed in one authoring process can be used by another one. Possibly, this problem can be solved by supporting queries in workflow specifications and incorporating some retrieval mechanisms for the (multimedia) document parts in the archive. 11
The presented CSCW teleservice is part of the GAMMA (Globally Accessible Multimedia Archives) project carried out at GMD-IPSI, Darmstadt, and IBM ENC, Heidelberg. It is targeted on the development of multimedia archives providing distinct services which are accessible via public networks ([17],[18],[19]). For the realization of the archives, we are using the object-oriented DBMS VODAK which is a research prototype under development at GMD-IPSI for the last six years. The described multimedia mail implementation for the introduced CSCW teleservice has been provided by GMD-FOKUS. Acknowledgement Thanks to K. Hofrichter, P. Hoepner, E. Moeller, H. Pusch, K. Röhr and G. Schürmann of GMD-FOKUS for providing comprehensive support with respect to our multimedia mail implementation. We would also like to thank Arthur Ozimek as well as Haris Stivaktakis of GMD-IPSI who implemented our archive server and client. Thanks go out as well to Jörg Haake (GMD-IPSI) who made helpful comments on an earlier version of this paper.
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[11] Klas, W., et al.: ‘‘VML - The VODAK Model Language Version 3.1’’, Technical Report, GMD-IPSI, July 1993 [12] Klas, W., Aberer, K., Neuhold, E.J.: ‘‘Object-Oriented Modeling for Hypermedia Systems using the VODAK Modeling Language (VML)’’, Object-Oriented Database Management Systems, NATO ASI Series, Springer Verlag, August 1993 [13] Möller, E., Neumann, L., Schürmann, G., Thomas, S., Weber, R., Wolf, F.: ‘‘The BERKOM Multimedia-Mail Teleservice’’, to be published in Computer Communications [14] Neuwirth, Christine M., Kaufer, David S., Chandhok, Ravinder, Morris, James H.: ‘‘Issues in the Design of Computer Support for Co-authoring and commenting’’, CSCW 90 Proceedings, Los Angeles, CA, October 1990, pp. 183-195 [15] Pusch, H.: Design and implementation of a global reference mechanism for arbitrary data objects, Computer Standards & Interfaces, to be published [16] Putz, W., Neuhold, E.J.: ‘‘is-news: a Multimedia Information System’’, Data Engineering Bulletin, Vol. 14, No. 3, September 1991 [17] Rakow, T.C. et al.: ‘‘Development of a Multimedia Archiving Teleservice using the DFR Standard’’, Proc. of the 2nd Int. WS on Advanced Teleservices and High Speed Communication Architectures, Heidelberg, Germany, September 1994, to be published by Springer [18] Thimm, H., Rakow, T.C.: ‘‘A DBMS-Based Multimedia Archiving Teleservice Incorporating Mail’’, Applications of Databases, Proc. of the 1st Int. Conf, Vadstena, Sweden, June 1994, pp. 281-298 [19] Thimm, H., Röhr, K., Rakow, T.C.: ‘‘A Mail-Based Teleservice for Archiving and Retrieving Dynamically Composable Multimedia Documents’’, Conf. Proc. Multimedia Transport and Teleservices, Vienna, Austria, November 1994, to be published by Kluwer Academic Publishers
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