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Distributed Multimedia Databases as Component of a Teleservice for Workflow
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Distributed Multimedia Databases as Component of a Teleservice for Workflow Management*
Heiko Thimm1, Ulrich Marder2, Günter Robbert2, and Klaus Meyer-Wegener2
1 - GMD - Integrated Publication and Information Systems Institute (IPSI)Dolivostr. 15, 64293 Darmstadt, Germany
e-mail: [email protected]
2 - Dresden University of Technology, Computer Science Department, Institute for Operating Systems, Databases, and Computer Networks
Dürerstr. 26, 01062 Dresden, Germanye-mail: {robbert, marder, kmw}@is2201.inf.tu-dresden.de
AbstractIn this paper, we present a concept and implementation of a largely dispersed multimedia data-base system which consists of several multimedia database systems. The users and applicationscan access the databases in various ways. Our solution also covers the administration of mediaobject duplicates.
The entire multimedia database system is a component of a teleservice for workflow man-agement that encourages multimedia. So-called multimedia annotations are attached to work-flows and stored in the database system. The annotations are automatically retrieved and trans-ported over networks to the users who perform preassigned parts of workflows. One strengthof our implementation is that it is based on the CORBA Object Broker standard which makesit open to other systems.
Keywords: Distributed Multimedia Database Systems, Multimedia Database Management Sys-tems, Multimedia Teleservices, Multimedia Enhanced Workflow Management
1 IntroductionWorkflow management systems (WFMS) are currently a hot topic in computer science [22, 23].Networks are spreading, PCs become more and more interconnected, such that data transfer ispossible. This is used already to cooperate within organizations and beyond. In many cases,however, it still takes place at a very low level, typically as mail or file transfer. Thus, the usersremain responsible for the decision about when to transfer what to whom. It is the issue of workflowmanagement to delegate some propagation tasks to the system. To be able to do so, the system needsinformation on rules, procedures, exceptions, etc. It than saves the users from remembering all therules [5].
Within the VORTEL project [4, 5, 6, 7, 26] we are specifying a generic platform for workflowmanagement as a teleservice to enable interoperability between heterogeneous and largelydistributed workflow management systems. This way, the growing demand for decentralizedworkflow management is supported. The VORTEL platform is to be generic in the sense that it isnot an executable system or a set of tools itself, but it has to be instantiated by using specific systems
* This work is partially granted by DeTeBerkom GmbH, Berlin, as project ‘‘Vorgangs-bearbeitungs Teleservice’’ (VORTEL) within the BERKOM II initiative.
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to become executable. Within the framework of VORTEL we encourage the use of multimedia datawithin workflow management. This is motivated by the fact that multimedia data accompanying aworkflow can improve the processing of workflows and enhances the traditionally strict formal na-ture of workflow management by an additional informal facet. For example, in addition to a textualdirective which explains how to complete a specific part of a workflow an audio recording whichgives further information can be provided.
In order to introduce multimedia, VORTEL provides the notion of a multimedia annotation whichis a piece of information attached to a step within a workflow. Multimedia annotations can be of thetypical media types supported by multimedia systems, i.e., TEXT, PICTURE, AUDIO, VIDEO.
Workflow management is an interesting application domain for multimedia. In this paper, we focuson the technical aspects of how to support multimedia within the framework of the VORTEL teleser-vice for workflow management. This support is based on a so-called Multimedia AnnotationDatabase (MM-ANDB) which is a distributed multi-database system consisting of multimediadatabases. The MM-ANDB stores and manages the multimedia annotations and provides essentialservices required by other VORTEL components. In designing the MM-ANDB we had to solvesome interesting problems such as the management of duplicates. We present our solutions to theseproblems. Furthermore, we describe a concrete implementation of a demonstrator which is basedon the two multimedia database management systems MOSS [10, 11, 15, 17, 18], developed at Dres-den University of Technology and University of Erlangen-Nürnberg, and AMOS [1, 19, 28, 32, 33,34, 35], developed at GMD-IPSI. The distribution and interoperability is implemented accordingto the Object Management Group’s (OMG) Common Object Request Broker Architecture (COR-BA). More precisely, we have used an Object Broker implementation developed by DEC.
The remainder of this paper is organized as follows. In section two, we give a brief overview of theVORTEL project. The role of multimedia database systems within VORTEL is explained in sectionthree. Our concept and implementation is described in section four and five, respectively. Relatedwork is discussed in section six and section seven concludes the paper.
2 VORTEL – Teleservice for Workflow ManagementVORTEL is a joint research project [4, 5, 6, 7, 26] of the Berkom Programme funded by DeTeBer-kom which is a consulting company of the German Telecom. DeTeBerkom’s activities are focusedtowards research and development of telecommunication applications. In Table 1, the members ofthe VORTEL project are listed.
Digital Equipment Corporation, Campus-based Engineering Center (CEC), Karlsruhe
IBM Deutschland Informationssysteme GmbH, European Networking Center (ENC), Heidelberg
Friedrich-Alexander-Universität Erlangen-Nürnberg, Computer Science Department, Erlangen
Fraunhofer-Gesellschaft, Institute for Software and Systems Technology (ISST), Dortmund
Dresden University of Technology, Computer Science Department, Dresden
German National Research Center for Information Technology (GMD), Integrated Publication andInformation Systems Institute (IPSI), Darmstadt
Table 1: Members of the VORTEL Consortium
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Project Objectives
The goal of VORTEL is to develop a generic platform for workflow management to enable inter-operability between largely dispersed systems. The requirements to be met are summarized below:
– Multi-vendor. The VORTEL platform needs to support existing platforms fromdifferent vendors which can be regarded as instances or specialization. This includes hardware and operating systems as well as applications and workflow managementsystems including their components.
– Interoperability. The interoperation of different workflow management systems and their components needs to be supported.
– Data Structures. Data structures that describe and encompass activities within aworkflow need to be represented according to international standards.
– Use of Existing Teleservices. The teleservices already specified and implemented in the Berkom research programme are to be evaluated and used as a basis forimplementing and instantiating the VORTEL platform.
– Use of Existing Teleservices. The teleservices already specified and implemented in the Berkom research programme are to be evaluated and used as a basis forimplementing and instantiating the VORTEL platform.
– Use of Existing Teleservices. The teleservices already specified and implemented inthe Berkom research programme are to be evaluated and used as a basis forimplementing and instantiating the VORTEL platform.
The specified platform is partially implemented according to application scenarios. In more concreteterms, we implement demonstrators to show the applicability of workflow management as ateleservice in an open and heterogeneous environment.
Architecture
The objectives introduced above lead to the definition of a generic workflow management systembackbone. It offers interfaces to plug in different components that provide the required workflowmanagement functionality (e.g., editing functionality). Considering the scope of a generic workflowmanagement system, a first coarse-grained architectural view of the system is given in Figure 1. Asshown, there is a Communication Bus which provides common interfaces to the different compo-nents and a means for communication among them. It should be emphasized that the architectureis meant to define a workflow management system not as a monolithic system but as a concept thatallows for incremental upgrading [5].
The role of the different components is as follows:
– The Communication Bus is the backbone of the workflow management system. Itimplements the interoperation and interconnection of the different components in thesystem. The purpose of the Communication Bus is twofold. At system-build-time it is the mechanism to integrate components. At system-operation-time it has the re-sponsibility to process and forward requests between components and to return theresults.
– The Workflow Definition Components allow to edit workflows to be supported by the workflow management system.
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User Agent
Workflow Definition Component
Workflow Engine
Workflow Database
Workflow Analysis Component
Local ApplicationProvider
Communication Bus
Figure 1: A sample instantiation of the general VORTEL architecture.
Global ApplicationMediator
– The User Agent is the component that interacts with the user who is involved in the workflow. It notifies him about the activities to be performed by him and providesaccess to the corresponding documents and tools. Since there may be (and usuallywill be) numerous users involved in the workflow, there are multiple instances of theuser agent, one for each user (in the figure indicated by the shadow behind the useragent).
– The Workflow Engine is the executant for the workflow model that determines theactivities to be performed next, allocates persons to the activities to be performed,resolves conflicts, etc. in the course of the workflow.
– The Workflow Database stores the workflow models and all information about theactual workflows themselves (e.g. current state, people and resources allocated in theworkflow). Furthermore, it also stores the multimedia annotations which potentially accompany the workflows. Note that, the workflow database does not contain the ar-tifacts to be processed within the workflows (e.g. forms to be completed).
– The Workflow Analysis Components are used for consistency checks on the model or for performing a workflow model validation or verification (e.g., in order to detect bottlenecks or deadlocks or for performing a resource planning on the model).
– Both, the Global Application Mediator (GAM) and the Local Application Provider (LAP) serve as components to integrate external applications (e.g. word processing systems). The GAM maintains information about the services and data availablewithin the entire system. Based on these information and actual parameter values, theGAM instructs the respective LAP to start the required application.
3 Role of Multimedia Database Systems within VORTELIn this section, we motivate to add multimedia annotations to workflow management systems in thecontext of VORTEL. Furthermore, we describe the functionality and design of the global Workflow
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Database of the VORTEL architecture. From these aspects, we derive the requirements for a respec-tive Multimedia Annotation Database System.
3.1 Multimedia Annotations within the VORTEL Workflow ModelThe general goal of adding multimedia annotations to workflow management systems is to makeusers’ lives easier. User not only means the end users, who are involved in workflow instances, butalso means the workflow modelers, who define new workflow types or analyze existing ones.
Such multimedia annotations are mostly used to add some explanations, instructions or somethinglike that to any object managed by a workflow management system, e.g. a workflow type, a specificactivity of a workflow instance, or a document which is used in some workflow(s). Nevertheless,multimedia annotations do not become part of the annotated objects but rather are in some senseattached to those objects. Thus, the same annotation can be used for several different objects and,obviously, each object can have attached to it several annotations.
A typical employment of multimedia annotations in workflow management systems is the detaileddescription of workflow types. Whereas keywords and short textual descriptions can be used tosearch for or browse through a list of workflow types, multimedia annotations are most suitable togive more detailed information on a specific workflow type, such as:
– audio comments on the purpose of the workflow type,
– images of the flow of control and data between the different activities,
– simulations of workflow types,
– training videos,
– useful hints for making decisions,and so on.
Of course, in order to give users of workflow management systems the opportunity to exploit theabove mentioned functionality, the User Agents must be extended to support creation andpresentation of multimedia annotations as well as some localisation mechanisms (e.g. WorkflowType Browser). Within the VORTEL project some special tools for handling multimedia annotationsare developed for demonstration purposes. However, we expect that the user interfaces of futureworkflow management systems will directly support the VORTEL global workflow databaseinterface which covers multimedia annotations, too.
3.2 The Global Workflow DatabaseThe global workflow database has to store every globally relevant information concerning workflowtypes and instances.
This includes
– Reference Data: any useful descriptional data which may help workflow users ormodelers to search for workflow types and to find out what task a specific workflow of that type will perform, which documents it creates, on which workflow engine(s) itcan be instantiated etc.
– Workflow Type Definitions: formal descriptions of workflow types which, amongother things, consist of
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– the definition of all activities, including the executants and external applica-tions which must be used to carry out the activity,
– the definition of the control flow between activities, such as sequences, parallelbranches (AND-split), conditional execution (OR-split), reunion of parallelbranches (AND-Join respectively OR-Join) etc.
– Workflow Instances: this part of the workflow database keeps track of all runningworkflows by monitoring their actual state (e.g. the last performed activity) and, fur-thermore, stores all historical information on completed (or aborted) workflows.
– Multimedia Annotations: the role of annotations which are also stored in the global workflow database has already been discussed in section 3.1.
Figure 2: Structure of the global workflow database for VORTEL.
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A simplified diagram of the global workflow database is shown in Figure 2 (using the notation ofthe Object Modelling Technique). According to the different roles of the workflow databasementioned above, the conceptual design of the database leads to four major components which maybe developed more or less independently. These four components are the Reference Database, theWorkflow Type Database, the Workflow State Database, and the Multimedia Annotation Database.For each database component the diagram of Figure 2 indicates only one entity which is the centralentity of the respective component. However, every component, except the annotation database,consists of many entities and relationships between them.
As stated earlier, it should be possible to attach multimedia annotations to almost every objectmanaged by a workflow management system. This requires relationships between the entity Multi-media Annotation on the one hand and several entities belonging to other components of the Work-flow Database on the other (see Figure 2). The relationship between Multimedia Annotation and theentity Workflow Type Description of the Reference Database, for example, allows a workflowmodeler to provide end users with vivid and comprehensible illustrations of the workflow types. But,the workflow modeler may also want to give other workflow modelers or analysts explanations orhints concerning the formal definition of the workflow types. Thus, a relationship between Multime-dia Annotation and the entity Workflow Type Definition of the Workflow Type Database is needed,too. Moreover, the acting persons of a running workflow may also sometimes wish to annotate a just
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completed activity before handing over control to the next actor, e.g. to justify or explain an unusualdecision. Such annotations have to be linked with the entity Workflow Instance of the WorkflowState Database, because they are workflow instance specific rather than workflow type specific.
3.3 Requirements for a Multimedia Annotation Database SystemIn the following, based on the previous explanations, we derive the requirements of a database sys-tem targeted at multimedia annotations. We call this system the Multimedia Annotation DatabaseSystem (MM-ANDB).
Referencing Multimedia Annotations from other DatabasesConventional database management systems (DBMS) are not very good in managing largeunstructured objects like media objects because they do not provide any type-specific functions (e.g.presentation, capture, format conversion) which can be applied to such objects. Consequently,particular multimedia database management systems (MM-DBMS) have to be used to storemultimedia annotations properly.
As explained above, several relationships exist between multimedia annotations and other parts ofthe global workflow database (which will be implemented using a relational or an object-orientedDBMS). Thus, one requirement is that multimedia annotations stored in a multimedia database sys-tem (MM-DBS) must have unique and stable identifiers (assigned and maintained by the MM-DBMS) which are qualified to serve as references to them. This means, e.g., that the identifier ofa multimedia annotation has to be the same as long as the annotation exists irrespective of any reorga-nization of the data set.
Physical DistributionOne fundamental assumption of VORTEL is that future workflows will be spread over severalindependent institutions or companies which are connected via wide-area networks (WAN). As aconsequence, there exist at least two reasons to physically distribute the multimedia annotationdatabase system:
– Performance (or costs, respectively). Accessing media objects via WANs is eithervery dissatisfying (low quality, long response-time) or very expensive because high bandwidth must be provided. Therefore, a local part of the MM-ANDB should be accessible via local-area networks (LAN) from each workstation used by workflow participants.
– Autonomy. Annotations may be somehow confidential, i.e., not be accessible forworkflow participants of other institutions. Hence, the opportunity to self-responsi-bly manage access rights must be granted to each institution participating in adistributed workflow management system. We consider physical distribution of theMM-ANDB to be the most suitable way to do this.
Of course, there are other advantages of physical distribution (e.g. high availability) and also somedisadvantages (e.g. the problem of managing distributed transactions). A general discussion of thesedisadvantages is given in [9].
Integration and Interoperability of multiple MM-DBMSDevelopment of MM-DBMS started only a few years ago. Therefore, until now there exist merelya handful of research prototypes which, in general, are based on different design concepts and
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provide varying functionality (see, e.g., the brief descriptions of the MM-DBMS MOSS and AMOSgiven in section 5). In our approach we intend to create a more powerful MM-DBMS by combiningthe strengths of multiple MM-DBMS. This requires defining common interfaces and protocols inorder to make multiple MM-DBMS appear as one ‘‘big’’ MM-DBMS.
Figure 3: A physically distributed Multimedia Annotation Database System
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4 A Distributed Multimedia Annotation Database System forVORTEL
According to the reasons discussed in section 3.3, we propose to have a local MM-DBS at each site(i.e., one that is installed within the respective LAN) and in addition to that several others which arenot locally available but accessible via WANs. Hence, our solution provides a MM-ANDB whichis physically distributed over a set of MM-DBSs. Figure 3 shows a sample configuration of such asystem.
The functionality to be provided by the distributed MM-ANDB must allow:
(1) direct access to each MM-DBS via object identifiers,(2) queries that span all MM-DBSs,(3) the generation and administration of media object duplicates.
In the following, we first describe how requirements (1) and (2) can be satisfied by introducing aso-called Annotation Database Manager (ANDB Manager). Then, we show how this solution can
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be enhanced in order to meet requirement (3) as well by introducing so-called Duplicate Managersand by adding more functionality to the ANDB Manager.
Providing the Access and Query Functionality
Figure 4: Annotation Database Managers to support the required access and queryfunctionality.
ReferenceDatabase Application
Annotation DatabaseManager
MM-DBMSMM-DBMS
references to multimediaannotations
registrationdata, raw data,indices
registrationdata, raw data,indices
SEARCH
ACCESS
ANNOTATION DATABASE INTERFACE
ACCESS
An ANDB Manager which handles the access to the distributed MM-ANDB is introduced (Figure4). Instead of one central ANDB Manager, each User Agent has its own ANDB Manager. The ANDBManager enables both, a direct access (via an object identifier) and a descriptive access (via a de-scriptive search request, i.e., a query) to the distributed MM-ANDB. In case of a direct access, theANDB Manager extracts the name of the MM-DBS to be contacted from the object identifier first.Then, it issues the request to this MM-DBS. In case of a descriptive search, in addition to the rawquery expression, the concrete database to which the query is to be submitted is specified. Otherwise,the query is submitted to all MM-DBSs of the global MM-ANDB (spanning query). The access func-tionality also includes a write access, i.e., the insertion of new multimedia annotations in the MM-ANDB.
The ANDB Manager also handles the network-based transport of the media objects from the data-base to the respective sites at which the multimedia annotation is to be presented as well as the otherway round.
Management of DuplicatesFor each MM-DBS there is a Duplicate Manager that handles duplicates of media objects (Figure5). In more precise terms, the Duplicate Managers manage references between originals and copiesby maintaining:
– for each stored copy a reference to the corresponding original, and– for each original a list of references to all existing copies.
Upon generation of a duplicate, the ANDB Manager notifies the Duplicate Managers of the MM-DBS which contains the original and the one in which the new duplicate is to be stored (Notification
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Application
Annotation DatabaseManager
Duplicate Manager
duplicate management data
SEARCH andACCESS
ANNOTATION DATABASE INTERFACE
MM-DBMS
registrationdata, raw data,indices
MM-DBMS
registrationdata, raw data,indices
duplicate management data
SEARCH andACCESS
NOTIFICATION DUPLICATE CREATION
NOTIFICATION DUPLICATE UPDATE
Figure 5: Duplicate Managers for the generation and administration of media object duplicates.
Duplicate Manager
Duplicate Generation). When a copy or an original of which copies have been made is modified,then the MM-DBS which contains the modified object notifies the respective other ones (Notifica-tion Duplicate Update). A MM-DBS which receives an Update Notification can react in variousways. For example, it can simply ignore the message, issue a message to the user, or automaticallyperform the requested update.
5 ImplementationIn the following, we describe our implementation of the MMANDB for the VORTEL demonstrator.As MM-DBSs we have used the two systems MOSS and AMOS which are both research prototypes.DEC’s Implementation of the CORBA compliant Object Request Broker has been employed to en-able the required communication between the components.
5.1 The Systems MOSS and AMOSMOSS (Media Object Storage System) is a research prototype of a multimedia object storingsystem that originated at the University of Erlangen-Nürnberg and is now under development at theDresden University of Technology [10, 11, 15, 17, 18].
Even the most advanced DBMS prototype (extended relational or object-oriented) do not providesufficient support for the management of multimedia data. In order to develop and evaluate ap-propriate mechanisms in isolation, MOSS has been designed to manage only those data. The far-endgoal is to identify the right mechanism that can be integrated into full-fledged DBMS prototypes.In the meantime, MOSS can be used in combination with a DBMS for standard formatted data. Thislacks some functionality (e.g. no spanning query expressions), but has already been used with suc-cess in real applications. For the MM-ANDB of VORTEL, MOSS alone can do the job.
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Figure 6: Design philosophy of the MOSS system.
APPLICATION
conventional DBMS
MOSSmedia object
identifier
Multimedia-DBMS
embedded conventionalDBMS-interface
MOSS application programminginterface
MOSS generates a unique identifier for each media object it stores. This media-object identifier(MO-ID) can, for instance, be kept in entity attributes of a conventional DBMS (as in the case ofa ‘‘photo’’ attribute of an employee; see Figure 6). In addition to the storage management of mediaobjects, MOSS also provides means for searching, processing and format-conversion of mediaobjects.
All media types (TEXT, IMAGE, AUDIO, GRAPHIC, VIDEO) are implemented as so-called Me-dia-specific Abstract Data Types (MADT). These MADTs provide type-safe operations for creation,retrieval, presentation and editing of media objects. All MADT functions are exported through anapplication programming interface. Further, it must be emphasized that format independency isanother advantage of the MADT concept. This will become obvious when considering thefollowing:
– If a user stores a media object in MOSS the respective MADT automaticallyrecognizes the format of the media object (in most cases). The media object then will be stored using an internal MOSS format which is determined by the MADT and maydiffer from the external format.
– Now, any user is able to retrieve this media object without taking care of its originalformat, because MOSS allows users to specify the desired external format of themedia objects (and, consequently, performs the appropriate format conversions, if necessary). Thus, users can store and retrieve media objects without having to use external format-conversion applications.
MOSS preserves some of the benefits of the relational data model by supporting a concept, calledsearch-set-concept, for contents-based searching for media objects. This search-set-conceptincludes the following features:
– creation of search-sets with media objects as elements,
– each media object can be member of arbitrary search sets, and set membership may change over time,
– the semantics of a search-set are determined by a so-called dictionary which is used toanalyze the colloquial content descriptions of each media object in the set (queries
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over the set are analyzed using the same dictionary and are then matched with thedescriptions),
– the usual set operations (unions, intersections, difference) can be applied to search-sets, too (the dictionary of the resulting set cannot be generated automatically fromthe two input sets; it must be compiled and attached to the set by the user).
AMOS (Active Media Object Store) is a research prototype of a MM-DBMS [1, 19, 28, 32, 33,34, 35] under development at GMD-IPSI.
Most multimedia applications involve a diversity of conventional datatypes like numbers, text, andtables combined with media data like images (bitmaps), graphics, audio, video and animations. Ear-ly research results in the area of multimedia systems have shown that object-oriented programmingand the usage of object-oriented DBMS are a very promising basis to provide for the multitude ofdatatypes and their manipulation features. However, besides those well-known concepts several oth-er techniques need to be employed by a MM-DBMS. Modelling features for time-dependency andsynchronized presentation of multimedia data as well as runtime support must be added and inte-grated into the system. Furthermore, presentations and control of presentations at the user’s worksta-tion requires a client/server architecture, specific buffering concepts, and networks supporting con-tinuous and isochronous transport protocols. The necessary access to existing multimedia data stores(e.g. CD-ROM systems) and databases requires flexible integration techniques for heterogeneoussystems.
The development of the AMOS system is geared towards the above mentioned concepts. These con-cepts are integrated within the existing object-oriented DBMS VODAK (‘‘Verteiltes Objektorien-tiertes DAtenbanKsystem1’’) [2, 13, 12 20]. Our development efforts include:
– an extension of VODAK’s data definition language to support temporal multimedia operations such as the simultaneous start of multiple media presentations [1],
– the integration of a storage management and object management component for con-tinuous data [19],
– the integration of a transport component for continuous data,
– the integration of a so-called Playout Management Service as a novel built-in data-base service which executes scripted multimedia presentations [32, 33, 34]. Withinthe framework of the Playout Management Service we investigate optimization is-sues for adaptations of multimedia presentations [35]. This is important for best-ef-fort based multimedia presentation services, i.e. presentation services which are notbased on end-to-end guaranteed quality of service. This research issue is jointly in-vestigated with the Oregon Graduate Institute of Science and Technology (OGI),Portland, OR, USA. Researchers of that institute have recently proposed an interest-ing approach for the specification of quality of service [27].
So far, several prototypes [25] and multimedia applications including workflow management forcooperative authoring of multimedia documents [29], multimedia archives [28, 30, 31], and simula-tion [8] have been developed based on AMOS. Thus, the concepts and implementations are going tobe constantly evaluated against user requirements. AMOS will make the VODAK DBMS a multi-media, object-oriented, and with respect to a client/server architecture a distributed DBMS.
1. This is the German term for distributed object-oriented database system.
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5.2 Realization of Distribution and Interoperability Based on CORBA
Implementation Architecture Overview
Figure 7: Implementation architecture of the multimedia annotation database systemfor the VORTEL demonstrator.
Browser
Ann. DB Mgr.references to multimediaannotations
registrationdata, raw data,indices
registrationdata, raw data,indices
ANNOTATION DATABASE INTERFACE
MOSS AMOSSUN/Solaris 2.4 or DEC Alpha/OSF1 SUN/Solaris 2.4
CORBA (DEC Object Broker 2.5b)
PC/Windows NT
PC/Windows NT
Reference-DBSybase 10 onSUN/Solaris 2.4
During the VORTEL project we have implemented a distributed MM-ANDB which is based on theconcepts shown in Figure 4 and 5. The implementation architecture of the MM-ANDBS is depictedin Figure 7. In our implementation of the MM-ANDBS we used MOSS and AMOS as serversexecuting on different network nodes. For the client side of the MM-ANDBS we implemented a firstprototype of the ANDB Manager which offers an easy-to-use API called Annotation DatabaseInterface to client-applications.
The communication between clients and servers is realized using CORBA . More precisely, we havechosen ObjectBroker version 2.5b developed by our project partner DEC. The decision to useCORBA for implementing the distributed MM-ANDBS was driven by the fact that it offers someuseful advantages for rapid development of distributed applications:
– easy-to-use Interface Definition Language (IDL) which is highly adequate to design and implement interfaces for client/server communication over net-works,
– programming on application layer (automatic generation of client and server skeletons) rather than on protocol or even transport layer,
– support of heterogeneity, because CORBA (i.e., ObjectBroker) isimplemented for many platforms.
Unfortunately, presently available implementations of CORBA like ObjectBroker 2.5b lack insupporting continuous data streams or - which would even be more desirable - some sort of
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module ANDB{
/*type definitions omitted...
*/
interface ANDBIF {
void Create(in TTypeDescr MO_TypeDescr, /* external format */in TRawData MO_RawData,in T_MO_Id original_MO_Id,/* specify in case
of duplicatecreation */
out T_MO_Id new_MO_Id)raises( UserException );
void Update(in T_MO_Id MO_Id,in TTypeDescr MO_TypeDescr, /* external format */in TRawData MO_RawData,
)raises( UserException );
void Delete(in T_MO_Id MO_Id
) raises( UserException );
void Get(in T_MO_Id MO_Id,in TTypeDescr MO_TypeDescr, /* external format */out TRawData MO_RawData
) raises( UserException );
void Query(in TQueryExpression queryExpression,out MO_IdList queryResult
)raises( UserException );
void Notify_Create(in T_MO_Id original_MO_Id,in T_MO_Id duplicate_MO_Id
)raises( UserException );
void GetInfo(in T_MO_Id MO_Id,out T_MO_Info MO_Info )
raises( UserException );
void GetServerProfile(out TServerProfile serverProfile
)raises( UserException );
};};
Figure 8: CORBA Interface for the Multimedia Annotation Database System
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multimedia network protocol. Therefore, in order to achieve high performance transport ofmultimedia data over network, additional communcation protocols not included in the CORBA 1.2specification must be employed. While implementing our prototype we have put aside this task,because with future implementations of the recently released CORBA 2.0 specification probablybetter solutions will be applicable.
Client/Server Interface
Prior to the use of CORBA, the interface must be defined in the IDL. The IDL-module for our firstprototype defines a minimum of eight methods which an ANDB server must be able to perform (seeFigure 8).
The eight methods are:
– Create. This method is designated for the creation of new media objects (MO). Asinput parameters this method expects a type description (MO_TypeDescr ), the rawdata stream (MO_RawData) and – if a duplicate of a MO is created – the MO-identi-fier of the original MO (original_MO_Id ). The type description presentlyconsists of a media type code (e.g. IMAGE, AUDIO) and a data format code (e. g.GIF, AU) while the raw data is represented by an unlimited byte sequence. In the caseof successful execution this method returns a unique MO-identifier (new_MO_Id).Otherwise, a so-called user exception is raised. Thereby, an error code and acorresponding error text is returned to the caller of the method (exception handling isthe same for all eight methods).
– Update. Using this method, the contents of an already existing MO (identified by itsMO_Id) can be updated. Analogously to Create a type description and the raw datastream must be supplied as parameters.
– Delete. This method is designated for deletion of existing media objects. As inputparameter only a MO_Id is required2.
– Get. This method is designated for retrieval of media objects by MO_Id. As inputparameters a MO_Id and a type description of the desired external format(MO_TypeDescr ) must be supplied. If the requested media object exists and theserver is able to create the specified external format, the object is returned as a bytesequence.
– Query. Using this method a search query can be sent to the server. If the server iscapable of processing the query, a (possibly empty) list of MO_Ids meeting thesearch conditions specified in the query is returned.
– Notify_Create. This method must be called on a server that stores a MO of which aduplicate has been created on a different server.
– GetInfo. This method should be used to get information on a specific MO (e.g. a listof external formats to which the server is able to transform it) before retrieving it.
– GetServerProfile. Using this method a client can get information about thecapabilities of a specific server (e.g. available MO types and external formats; doesthe server support real-time applications?).
2. Of course, we know that this method will cause a serious problem concerning external references to MOs, because deleting a MOwill invalidate all external references to it. Thus, we will have to spend some time on this in the near future.
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Figure 9: The ANDB Client which serves as user interface to exploit the ANDB Manager.
Figure 10: Presentation of multimedia annotations using the ANDB Client.
ANDB Manager and ANDB Client
The ANDB Manager is implemented as a Dynamic Link Library. It is designed to perform the fol-lowing tasks:
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– CORBA-interface calls (thus making the use of CORBA transparent toapplications),
– presentations, e.g. playing audio, displaying images,
– server selection respectively server switching, e.g. switching between aMOSS- and an AMOS-server, and
– exception handling on client-side.
For demonstration purposes, we currently use a simple user interface called ANDB Client whichenables a user to work with the ANDB Manager. Figure 9 and 10 show two screen shots of such ademonstration.
6 Related WorkThe area of MM-DBS is a very active research area. Numerous research prototypes based on differ-ent architectural approaches have been proposed within the last few years. The most prominent re-search issues of this area include data modelling for multimedia applications [1], storage manage-ment [16] and buffer management for continuous data [19], support of distributed architectures [3],and support of multimedia presentations [32, 33, 34, 35, 27] especially the synchronization aspect[14].
To our knowledge, design concepts for distributed MM-DBS which consist of several largely dis-persed, heterogeneous, and autonomous DBS connected via WAN have not been proposed before.Such concepts are not only useful for workflow management as a teleservice, but for many otherpurposes as well. For example, they can be used for archiving and retrieval applications [28, 30, 31]or multimedia information systems (e.g. virtual multimedia product catalog, multimedia calendarof events) which need to be provided to largely dispersed users.
In comparison to the World Wide Web (WWW) the strength of our approach is that it is based ondatabase technology. Thus, mechanisms for, e.g., access control and data security which are offeredby DBMS allow to satisfy the special needs of such applications.
The CORBA standard has been used before for distributed multimedia systems. For example, theMultimedia System Services architecture proposed jointly by HP, IBM and SunSoft provides multi-media service abstractions through CORBA. An overview of this architecture is given in [21].
So far, not much attention has been paid to the use of multimedia information for workflow manage-ment. Hence, there exists only little experience, e.g. [29], in this area. We hope that the VORTELproject can stimulate respective activities by developers of workflow management systems.
Recently, we have started to interact with the Workflow Management Coalition (WfMC) [36, 37]which members are workflow vendors, universities, and other institutions. Currently, the WfMC isworking on a specification for interoperable workflow management systems for which the VORTELproject can provide helpful hints.
7 ConclusionIn this paper, we presented the requirements and a concrete approach for a distributed multimediaannotation database system as a component of a novel teleservice for workflow management. The
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given discussion on the use of multimedia annotations for workflow management purposes providesmany ideas which are relevant for workflow management in general. The main contribution of thework reported is our general concept for a largely dispersed distributed MM-DBS which itself con-sists of several autonomous MM-DBS. Convenient access to this system is offered to the users andapplication programs. We believe that the shown implementation which is based on the CORBAstandard provides helpful hints for other project in this area.
A teleservice for workflow management such as the one developed within the VORTEL project canprovide a wide spectrum of services to enable and support workflow management within distributedorganizations and among different organizations [4]. These services can cover, e.g., the provisionof a respective hardware and software infrastructure such that customers need not to deal themselveswith the installation and maintenance of such workflow management infrastructure. In the idealcase, the customers should be able to use the infrastructure by just connecting their computing envi-ronment to a ‘‘workflow management outlet’’ analogously to the telephony domain where users justneed to connect their telephone. A further sample service that can be offered is the provision of ageneric library of predefined workflows or consulting work with respect to the modelling of individ-ual workflow types. We believe that support of multimedia data is an important factor to achievea high user acceptance for such a novel teleservice which can be seen as a perfect application forthe currently evolving global information super highway.
AckknowledgementAll other members of the VORTEL project have contributed to this paper by supporting a vital discussionon the subject reported in this paper. We would like to express our deep gratitude to them and also to the De-TeBerkom for their project funding.
References1. Aberer, K., Klas, W.: ‘‘Supporting Temporal Multimedia Operations in Object-Oriented Database Sys-
tems”, Proc. of IEEE Multimedia Computing and Systems, Boston, USA, May 1994, pp. 352-3612. Aberer, K., Fischer, G.: ‘‘Semantic Query Optimization for Methods in Object-Oriented Database Sys-
tems’’, Proc. of the 11th Int. Conf. on Data Engineering, Taipei, Taiwan, March 1995, pp. 70-793. Berra, P.B., Chen, C.Y.R., Ghafoor, A., Lin, C.C., Little, D.C., Shin, D.: ‘‘Architecture for distributed
multimedia database systems’’, Computer Communications, vol. 13, May 1990, pp. 217-2314. Böhm, M., Deiters, W., Friedrich, M., Lindert, F., Schulze, W.: ‘‘Workflow Management as
Teleservice”, accepted for 7th Joint European Networking Conference JENC7, Budapest, May 13–161996
5. Deiters, W., Haake, J., Jablonski, S. and Meyer-Wegener, K.:‘‘BERKOM Projekt Vorgangsbearbeitungs-Teleservice VORTEL”, Coarse specification, DeTeBerkom, Berlin, 1994
6. Deiters, W., Friedrich, M., Lindert, F.: ‘‘Der Vorgangsbearbeitungs-Teledienst zur Integration vonVorgangssteuerungssystemen”, Telekooperations-Systeme in dezentralen Organisationen, Workshopof the GI-Fachgruppe 5.5.1, 22.-23. Februar 1996, Berlin, to be published
7. Deiters, W., Friedrich, M., Lindert, F.: ‘‘VORTEL– Eine Integrationsplattfrom zur Steuerung verteilterArbeitsprozesse”, in GI Softwaretechnik Trends, Band 15, Heft 4, ISSN 0720–8928, November 1995
8. Deegener, M., John, W., Kühnapfel, B., Löhr, M., Lux, G., Wirth, H.: ‘‘A Basic Architecture for theDevelopment of a Distributed Interactive Simulator”, in Breitenecker, F., and Husinsky, I. (Ed.) Proc.EUROSIM ‘95, Vienna, Austria, September, Elsevier, pp. 357-362
9. Gray, J., Reuter, A.: ‘‘Transaction Processing: Concepts and Techniques’’, Morgan Kaufmann Publish-ers, San Mateo, CA, 1993
10. Käckenhoff, R., Merten, D., Meyer-Wegener, K.: ‘‘Eine vergleichende Untersuchung derSpeicherungsformen für multimediale Datenobjekte’’, in: Stucky, W., Oberweis, A. (Ed):Datenbanksysteme in Büro, Technik und Wissenschaft, GI-Fachtagung Braunschweig, 3.-5. März 1993,Springer 1993, pp. 164-180
19
11. Käckenhoff, R., Merten, D., and Meyer-Wegener, K.,‘‘MOSS as Multimedia Object Server – ExtendedSummary,” in Multimedia: Advanced Teleservices and High Speed Communication Architectures,Proc. 2nd Int. Workshop - IWACA ’94 (Heidelberg, Sept. 26-28, 1994), ed. R. Steinmetz, Lecture Notesin Computer Science vol. 868, Springer-Verlag, Berlin 1994, pp. 413-425
12. Klas, W.:‘‘Tailoring an Object-Oriented Database System to Integrate External Multimedia Devices’’,Int. Workshop on Heterogeneous Databases and Semantic Interoperability, Boulder, February 1992
13. Klas, W., Aberer, K., Neuhold, E.J.: ‘‘Object-Oriented Modeling for Hypermedia Systems using the VO-DAK Modeling Language (VML)’’, Object-Oriented Database Management Systems, NATO ASI Se-ries, Springer Verlag Berlin Heidelberg, August 1993
14. Little, T.D.C., Ghafoor, A.:‘‘Synchronization and Storage Models for Multimedia Objects’’, IEEE Jour-nal on selected areas in communications, 8(3), April 1990, pp. 413-427
15. Marder, U., Merten, D.: ‘‘Systempufferverwaltung in Multimedia-Datenbankverwaltungssystemen’’ in:Lausen, G. (Ed): Datenbanksysteme in Büro, Technik und Wissenschaft, GI-Fachtagung Dresden,22.-24. März 1995, Springer 1995, pp. 179-193
16. Maier D., Walpole, J., and Staehli R.: ‘‘Storage System Architectures for Continuous Media Data’’,FOFO’93 Proceedings, Lecture Notes in Computer Science, Vol. 730, 1993, Spinger-Verlag, pp. 1-18
17. Meyer-Wegener, K.: ‘‘Multimedia-Datenbanken’’, in German, Reihe ‘‘Leitfäden der Angewandten In-formatik’’, B.G. Teubner Stuttgart 1991
18. Meyer-Wegener, K.: ‘‘Database Management for Multimedia Applications’’ in Encarnacao, J.L., Foley,J.D. (Eds.): Multimedia: System Architectures and Applications, Springer Verlag 1994, pp. 105 - 119
19. Moser, F., Kraiss, A., Klas, W.: ‘‘L/MRP: A Buffer Management Strategy for Interactive ContinuousData Flows in a Multimedia DBMS’’, Proc. of the 21th Int. Conf. of Very Large Data Bases (VLDB’95),Zürich, Switzerland, September 1995, pp. 275-286
20. Muth, P., Rakow, T.C., Weikum, G., Broessler, P., Hasse, Ch.: ‘‘Semantic Concurrency Control in Ob-ject-Oriented Database Systems’’, Proc. of IEEE Ninth International Conference on Data Engineering,Washington DC, 1993, pp. 233-242
21. ‘‘Middleware System Services Architecture’’ in John F. Koegel Buford (Ed): Multimedia Systems, ACMPress, Addison-Wesley Publishing Company, 1994, pp. 221-244
22. Proceedings of the third IEEE Workshop Enabling Technologies: Infrastructure for CollaborativeEnterprise (WET ICE), Morgantown, WV, 1994
23. Proceedings of the 4th International Working Conference on Dynamic Modelling and InformationSystems, Noordwijkerhout, Netherlands, September 1994
24. Publications of the Workflow Management Coalition (WfMC),http://www.aiai.ed.ac.uk:80/WfMC/index.html.
25. Rakow, T.C., Muth, P.: ‘‘The V3 Video Server - Managing Analog and Digital Video Clips’’, Proceed-ings ACM SIGMOD ’93 Conference, Washington DC, May 1993, pp. 556-557
26. Schulze, W., Böhm, M.: ‘‘Interoperability Issues in Workflow-Management-Systems”, Proceedings ofthe European Business Process & Workflow Conference, Frankfurt, 6.-8. November 1995
27. Staehli, R., Walpole, J., Maier, D.: ‘‘ A quality-of-service specification for multimedia presentations’’ ,ACM Multimedia Systems Journal, Vol.3, Number 5/6, 1995, ACM Press, Springer, pp. 251-263
28. Thimm, H., Rakow, T.C.: ‘‘A Database Management System-Based Multimedia Archiving TeleserviceIncorporating Mail’’, Proc. of the 1st Int. Conf. on Applications of Databases, Vadstena, Sweden, June1994, Springer LNCS 819, pp. 281-298
29. Thimm, H.: ‘‘A Multimedia Enhanced CSCW Teleservice for Wide Area Cooperative Authoring ofMultimedia Documents’’, position paper to the ACM CSCW’94 WS on Distributed Systems, Multimedia,and Infrastructure Support in CSCW, Chapel Hill, NC, USA, October 1994, ACM SIGOIS Bulletin, De-cember 1994, Vol. 15, No.2, pp. 49-57
30. Thimm, H., Röhr, K., Rakow, T.C.: ‘‘A Mail-Based Teleservice Architecture for Archiving and Retriev-ing Dynamically Composable Multimedia Documents’’, Proc. of the Int. COST 237 Workshop, Multi-media Transport and Teleservices, Vienna, Austria, November 1994, Springer LNCS 882, pp. 14-34
31. Thimm, H., Rakow, T.C., Neuhold, E.J.:‘‘Using Multimedia Archives for Hypermedia Applications inOpen Networks’’, Kongress des Münchner Kreis, in Band 21, Reihe ‘‘Telecommunications’’, 1995, Her-ausgeber/Editor: J. Eberspächer, Springer Verlag, pp. 153-176
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32. Thimm, H., Klas, W.: ‘‘Reactive Playout Management - Adapting Multimedia Presentations to Contra-dictory Constraints’’, Arbeitspapiere der GMD No. 916, St. Augustin, June 1995
33. Thimm, H., Klas, W.: ‘‘Playout Management - An Integrated Service of a Multimedia Database Manage-ment System’’, First International Workshop on Multi-Media Database Management Systems, BlueMountain Lake, NY, USA, August 28-30, IEEE Computer Society Press, 1995, pp. 38-47
34. Thimm, H., Klas, W.: ‘‘Playout Management in Multimedia Database Systems’’, 60-pages invited bookchapter, in Nwosu, K., Berra, B., Thuraisingham, B. (Editors): ‘‘Design and Implementation of Multime-dia Database Management Systems’’, Kluwer Academic Publishers, to be published
35. Thimm, H., Klas, W.: ‘‘�-Sets for Optimized Reactive Adaptive Playout Management in DistributedMultimedia Database Systems’’, accepted conference paper, IEEE 12th International Conference onData Engineering, Feb. 26 - March 1, 1996, New Orleans, La., USA
36. WfMC: Glossary, November 199437. WfMC: Workflow Application Programming Interface (WAPI) Specification, Draft, Request for Com-
ments, Document No. WFMC-TC-1009, February 24th, 1995
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