In this paper, we describe the approach to achieve a high level of interoperability in the eduSource. The eduSource project is a pan-Canadian collaborative project to create a testbed of linked and interoperable learning object repositories (LOR). Two interoperability mechanisms will support linkage of LORs. A semantic cobblestone supports connecting the LOR into the eduSource network and will provide metadata and ontology mapping facilities. The linkage of eduSource network with other metadata initiatives will be supported via gateway mechanism.
Learning object repositories, Interoperability, P2P systems, Ontologies, Semantic web
The huge uptake of web technology in education and training has generated a flurry of un-coordinated activity developing digital learning objects - images, animations, computer applets or textual content which could be used in the processes of education and training. To support interoperability between learning and business systems several standards for describing metadata (MD) have been developed (IEEE LOM, IMS specifications, SCORM). Centralized digital (LORs) evolved as a means of collecting and cataloguing these assets with hopes of reducing the redundancy of development and enabling others to build on the aggregated ideas and designs. Unfortunately, a single centralized repository is unlikely to be of sufficient size to accommodate all of the web-based learning objects that have or will be created. Recent developments in peer-to-peer web technology have made it possible for individuals to amass local collections of entertainment content. Two projects exploiting peer-to-peer technology for learning objects are currently under development. The POOL project  concentrates on the heterogeneous infrastructure and end-user tools utilizing CanCore MD standard to connect individual and organizational repositories. Edutella  is a prototype peer-to-peer network which builds in a structured query service to help locate learning objects, an annotation service to allow users to comment on learning objects, and a mediation service to join MD from different sources. The eduSource projects is developing an infrastructure to connect centralized, harvested and peer-to-peer repositories.
The POOL project (www.edusplash.net) ran from 1999 to 2002. One of its major goals was to build an infrastructure for connecting heterogeneous repositories into one network. The infrastructure used a peer-to-peer model in which nodes could be individual repositories (called SPLASH) or community or enterprise repositories (PONDs). PONDS were connected to the POOL network using a specialized peer performing both functions of a gateway and wrapper. The POOL network uses JXTA peering protocol using CanCore/IMS MD profile/specification to exchange MD. Connected PONDs communicated using wrappers either via HTTP and CGI or XML-RPC protocol. The wrapper also performs the MD schema translation functions that are needed. The network supported a high autonomy for the repositories, but this required creating a specialized wrapper translating between the MD schemas and communication protocols.
The eduSource project (www.edusource.ca) is bringing together major LOR players in Canada to create an open infrastructure for linking interoperable LORs. The infrastructure will support a wide range of services with high autonomy and breadth of functionality with ease of connecting a new system into the infrastructure and ease of use of existing systems. The eduSource aims at creating a system which is both open to new services becoming participants in the system and existing systems connecting to the eduSource. The first implementation of the eduSource infrastructure is expected in Fall 2003. The interoperability solution will initially support tools and services of project partners and will seek the linkages to other international initiatives.
The interoperability solution for the eduSource project aims to provide an effective and expandable infrastructure which conforms to the IMS DRI specification and provides a generic solution for connectivity to other major initiatives such as OAI, NSDL, and the Edutella project. The solution builds on open standards and enables any interested party to connect to the eduSource network and access its services. The eduSource project uses the lessons learned from other projects and specifically (in the area of interoperability) the POOL project.
The backbone of the interoperability is the eduSource Communication Language (ECL) which implements the core functions defined in the IMS Digital Repository Interoperability reference model . A primary communication protocol in eduSource is SOAP and ECL is implemented as asynchronous SOAP messages. The default MD standard selected for the eduSource is Cancore/IEEE LOM (www.cancore.org). The eduSource infrastructure makes no assumptions about the format of MD stored in the repositories participating in the network. The repositories store MD in their local format and MD is available and can be used by other services and tools in original form or mapped into other supported standards.
Such a high level of autonomy typically makes it difficult to add a new component into the network. In eduSource we alleviate this problem by providing a highly configurable connector, the semantic cobblestone, with predefined mapping mechanisms for the most common MD schemas along with the ability to expand its functionality by defining additional mappings. In addition to mapping between MD schemas the connector enables to define mapping at the deeper semantic level. This is necessary for mapping between taxonomical or ontological structures used as sources of values for the MD elements, for example in the classification element. The ability to map between two ontological structures is essential for allowing individual repositories to expand MD schema with elements supporting local community needs.The third function of semantic cobblestone is to translate between repository native communication protocol and ECL. We do not consider this function to be as essential as implementation of the ECL over the SOAP protocol, which is supported with libraries simplifying the process.
The internal eduSource infrastructure is being implemented using web services model with the envisioned semantic web services extension . The initial set of services available in the eduSource network are repositories for storing LOs, MD repositories for storing LO MD, tagging tools for creating MD records, search tools for searching LOs, aggregation tools for aggregating LOs into lessons and a digital right management component for handling copyrighted materials. Similar to POOL, the eduSource infrastructure supports organizational and individual (peer-to-peer) repositories.
Although the eduSource internal protocol provides a flexible and efficient solution it is unlikely that well established repositories and resources will invest resources and convert their protocols to the ECL. However, the ability of the eduSource project to connect to other established protocols and major initiatives is of the utmost importance to the project participants. eduSource addresses the problem of outside interoperability by providing a second type of mediator simply called eduSource gateway. eduSource gateway is modeled after the design patter of an adapter functioning at the network level. The range of the functionality is similar to that of the semantic cobblestone, but the main function of the gateway is to mediate between ECL and communication protocols used by the outside systems. Two protocols being implemented at the beginning are OAI PMH and Z39.50. The gateway component is being developed as an open source product by the eduSource community with a clearly defined architecture of chained handlers which makes it easy to incorporate a new functionality or update and existing one. Another specific functionality the gateway will perform is a selector of internal eduSource services for the incoming requests. This functionality has been identified as important but will require more attention in near future