High-level brokerage services for the e-learning domain
Introduction
The Object Management Group (OMG) is an open membership, not-for-profit consortium that produces and maintains computer industry specifications for interoperable enterprise applications. OMG's own middleware platform is CORBA. Nowadays, one of the hot topics at the OMG is the specification of services and facilities in specific vertical markets through Domain CORBA Facilities. The application of CORBA technologies improves standardization in a specific domain through the definition of those interfaces that must be provided by the core software components used to build applications in the domain. This paper describes a draft proposal for a Domain CORBA Facility for educational brokerage that defines the software services needed in an intermediation framework for learning objects. Currently, e-learning standardization (Section 2) is a very active process with very important actors involved.
Domain CORBA Facilities are defined using the OMG's Interface Definition Language (IDL). IDL itself is not tied to any specific language environment or platform. This is what made it possible for ISO to adopt IDL as a standard without any specific reference to CORBA. A set of IDL modules containing specifications of IDL interfaces, valuetypes and other datatypes is a declarative syntactic model of a system. Such a model can be used to reason about the validity or lack thereof of relationships among the entities specified using the rules of relationships among IDL declarated entities like containment, inheritance, etc. An IDL specification is an object model that can be implemented on a CORBA platform that will implicitly verify the syntactic validity of any attempt to use any part of the system.
Nevertheless, such a specification does not contain much formal information about the meaning of the operations of the interfaces or of the elements of the datatypes declared, nor about the constraints that apply to them. In traditional CORBA specifications such information has been included in a normative but informal description in English. A well-conceived facility is based on an underlying semantic model that is independent of the target platform. Nevertheless, the model could not be distilled explicitly, and this is the case with OMG domain specifications because the model for most of them is not expressed separately from its IDL interfaces. As their models are hidden, these facilities have received neither the recognition nor the widespread implementation and use that they deserve outside of the CORBA world. The OMG's Model Driven Architecture (MDA) [18] is a multi-platform specification that tries to overcome the drawbacks mentioned above. This paper proposes (Section 3) an MDA-oriented methodology to produce standardized vertical facilities with a visible and separate underlying conceptual model. The different stages involved in this process offer a rich semantic model to be used both for developers of implementations compliant with the facility and users of the defined services.
The whole process defined by the proposed methodology is developed through 4 Reference model, 5 Use case model, 6 Analysis model, 7 Reference architecture, 8 Design model. The outcome is a set of IDL specifications that define the behavior of distributed standards-driven and interoperable brokerage systems for learning objects. Finally, from our experience in the development of a product compliant with these specifications, a set of best-practice guidelines are included in Section 9.
Section snippets
Standardization in the e-learning domain
The e-learning standardization process is an active, continuously evolving process that will last for years to come, until a clear, precise, and generally accepted set of standards for educational-related systems is developed. Among the main contributors to this effort let us mention the IEEE's Learning Technology Standardization Committee (LTSC), the IMS Global Learning Consortium, the Aviation Industry CBT Committee (AICC), the US Department of Defense's Advanced Distributed Learning (ADL)
Methodology
In order to identify the most suitable services to be included in a draft proposal for a Domain CORBA Facility for educational brokerage, we defined a strict and systematic methodology for domain-specific service specification. The proposed methodology follows the guidelines established by the OMG's Model Driven Architecture (MDA) [18] and is based on the Unified Software Development Process [15] together with the recommendations by Bass et al. [6]. Nevertheless, the Unified Process guidelines
Reference model
As stated before, the first stage in the methodology is the identification of a Reference Model (step 1 in Fig. 4). This is a standard decomposition of a known problem into parts that cooperatively solve the target problem from the clients' viewpoint, i.e., it is a business model where the key agents participating in the domain under study and the data flows among them are identified. For this identification, an exhaustive analysis of the most outstanding e-learning systems (some comparatives
Use case model
Once established the high level components of the system in the Reference Model, their functional requirements from clients' viewpoint must be captured and documented. Firstly, it is necessary to model the clients of the domain under consideration. We decided to use the ERILE recommendation [17], which is the pioneer specification identifying the actors that should be considered in standardized e-learning environments and it is widely recognized among the e-learning community. ERILE identifies
Analysis model
The Use Case Model is the starting point to define an Analysis Model (step 3 in Fig. 4). In analysis use cases are further studied from the designer's point of view. As a consequence, a deeper knowledge of the system is achieved. From an initial analysis of the use cases, a set of analysis packages for each element of the Reference Model is defined. Analysis packages groups those use cases that are functionally related. Then, every package is analyzed separately, possibly by different teams, in
Reference architecture
Service packages from the Analysis Model are the foundation for the Reference Architecture (step 4 in Fig. 4), which is the Platform Independent Model in our proposed methodology. It is a decomposition of the Reference Model into a set of components that provide the functionality identified along the previous stages. Note that, in a general sense, the objective is the definition of a set of services to facilitate and speed up the development of standardized distributed and interoperable final
Design model
As the Reference Architecture includes only classes from the Analysis Model, it is implementation independent and purely conceptual. The next step lies in the elaboration of a Design Model (step 5 in Fig. 4) using the constructs and concepts of a specific development environment for building distributed applications. As our final objective is the definition of a new Domain CORBA Facility for e-learning brokerage we chose CORBA as the implementation/deployment environment.
The Reference
Prototype
Different vendors claiming compliance with the CORBAlearn specification will offer products that provide the services defined in these interfaces. Over these basic services, developers of final applications build the wrapper, where user interfaces are embedded and additional value-added services may be included. There is no restriction in terms of wrapper technology. The only assumption is that it is able to use CORBAlearn services through a CORBA software bus, which may be accessed from most
Summary
Nowadays, one of the hot topics at the OMG is the specification of services and facilities in specific vertical markets through Domain CORBA Facilities. These specifications consist of interfaces written in OMG IDL with accompanying semantic description in english text. A well-conceived facility is based on an underlying semantic model that is independent of the target platform. Nevertheless, the model could not be distilled explicitly, and this is the case with OMG domain specifications
Luis Anido received the Telecommunication Engineering (1997) degree (with Honors by the Spanish Department of Science and Education and by the Galician Regional Government) and a PhD in Telecommunication Engineering (2001) degree from the University of Vigo. He has been also awarded by the Galician Royal Academy of Sciences. Currently, he is an Associate Professor at the Telematics Engineering Department of the University of Vigo. His main interests are in the field of New Information
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Luis Anido received the Telecommunication Engineering (1997) degree (with Honors by the Spanish Department of Science and Education and by the Galician Regional Government) and a PhD in Telecommunication Engineering (2001) degree from the University of Vigo. He has been also awarded by the Galician Royal Academy of Sciences. Currently, he is an Associate Professor at the Telematics Engineering Department of the University of Vigo. His main interests are in the field of New Information Technologies applied to distance learning and in the area of Object-oriented distributed systems. He has been hired by the European Committee of Standardization (CEN) to develop two CEN Workshop Agreements (CWA) related to learning technologies.
Judith Rodrı́guez received her Telecommunication Engineering (1999) degree from the University of Vigo. In addition to teaching, her main interests are in the Educational Metadata and Information Retrieval. Currently, she is pursuing her PhD in the area of learning objects brokerage.
Manuel Caeiro received the Telecommunication Engineering (1999) degree from the University of Vigo. Currently, he teaches Computer Architecture and Software Engineering at the Telecommunication School of the University of Vigo where he is working towards his PhD in the area of Workflow Management in e-learning environments.
Juan M. Santos is a Telecommunication Engineering (1998). He has been involved in several projects related to distance learning and e-commerce. Now, he is Assistant Professor at the University of Vigo. His PhD is related to the application of the Semantic Web concepts to improve personalized learning environments.