1. BUILDING A DIGITAL REPOSITORY FOR LEARNING RESOURCES
Panagiotis Anagnostou1,2, Alexander Grigorov1,3
1Sofia University, Faculty of Mathematics and Informatics (BULGARIA)
2Business Administration Institute, Patras (GREECE)
3Institute of Mathematics and Informatics, Bulgarian Academy of Sciences (BULGARIA)

2. Introduction
One of the main advantages of using digital repositories in the e-learning process is that they provide mechanisms to encourage the discovery, exchange and reuse of learning resources.
Digital repositories are already well established throughout many countries in the European Union and in the US. Digital repositories are on their way to become a permanent part of the scholarly communication and documentation research infrastructure

3. Digital Repositories DSpace
free, open source software platform for building repositories of digital assets
designed by developers at the MIT Libraries and HP Labs
currently is used by over 250 institutions
A drawback of DSpace is that it uses a fixed web interface and cannot be easily integrated in other systems.

4. Digital Repositories (cont.)
ARIADNE
European educational digital library project initiated in 1996 by the European Commission’s telematics for education and training program.
a distributed digital library of education resources
semi-automatically generation of metadata

5. Digital Repositories (cont.)
Fedora
an open source, digital object repository system
Fedora supports flexible and extensible digital objects, which are containers for metadata, one or more representations of the content and relationships to other information resources.
Fedora's digital objects provide building blocks to support uniform management and access to heterogeneous content including books, images, articles, datasets, multi-media, and more.

6. Digital Repositories (cont.)
Fedora
Fedora is implemented as a set of web services that provide full programmatic management of digital objects as well and search and access to multiple representations of objects.
Fedora is particularly well suited to exist in a broader web service framework and act as the foundation layer for a variety of multi-tiered systems, service-oriented architectures, and end-user applications.

7. Digital Repositories (cont.)
Within the EC funded TENCompetence project an open source system LearnWeb2.0 has been developed for stimulating knowledge sharing, knowledge management and the transformation of information into knowledge into communities of practices.
Essential parts of the system are the knowledge repository and the Knowledge Resource Sharing and Management (KRSM) web services, which allow access and management of the repository. Fedora has been selected as a basic platform for the repository.

8. Digital Repositories (cont.)
The goal of the EC-supported Share.TEC project has been to push innovation into initial and in-service Teacher Education (TE). Share.TEC has undertaken to build an advanced user-focused system dedicated specifically to fostering a stronger digital culture in the TE.
The main component in the Share.TEC system is the central repository contains metadata representing resources from the Teacher Education domain.

9. Digital Repositories (cont.)
These metadata are represented in the Common Metadata Model (CMM) format and are collected from various sources: partners’ local metadata repositories and external repositories or additional sources containing such metadata.
The other main component of the system is the central portal where the user of the Share.TEC system can communicate with all of its components and to specify what services she/he needs from the system.

10. Requirements for the digital repository
Creation and management of digital resources - this includes: uploading and storing resources and metadata in the repository; editing metadata of existing resources;
Sharing of digital learning resources by providing free access;

11. Requirements for the digital repository (cont.)
Search for resources in the system repository (full text search in titles and descriptions, search by keywords, by classification categories, by tags, ordering the results by relevance);
Search for available resources from a number of existing Web 2.0 tools (such as YouTube, Flickr, etc.) (optional);

12. Requirements for the digital repository (cont.)
Social tools: commenting, tagging and rating of resources;
Support for sharing the resources within social networks (FaceBook, Twitter, Google+);
Classification of resources, support and management of classification taxonomies;

13. Requirements for the digital repository (cont.)
Visualization of different types of resources (videos, pictures, text, HTML, etc.);
Recommendation of learning resources;
Multi language interface and multi language support for the resources and metadata;
User management and registration;
User authentication and authorization;
Interoperability.

14. Common Data Model
In order to meet the requirement we have created a Common Data Model for the organization and representation of learning resources. It is based on standards to allow the reuse of learning resources and offer interoperability among heterogeneous e-learning systems.
The model consists of three parts:
Structural ontology;
Classification taxonomy;
Metadata.

15. Structural ontology The Structural Ontology defines
digital objects (learning resources, users, comments, tags, ratings, etc.);
the hierarchy of the objects;
digital objects properties (for example: width and height of a picture; width, height and duration of a video, etc.)
relationships (between resources, users, comments, ratings, etc.).
The ontology is developed in OWL

16. Classification taxonomy
The Classification taxonomy is used for the classification of the learning resources.
The taxonomy is built using SKOS (Simple Knowledge Organization System) - a formal language designed for representation of thesauri, classification schemes and taxonomies.
SKOS is built upon RDF and RDFS. The model allows the use of several distinct classification taxonomies.
The taxonomies can also be expressed in OWL.

17. Metadata
The Metadata can be presented in one of the standard formats Dublin Core and LOM (Learning Object Metadata).
However, we recommend the use of Dublin Core for its simplicity and wide acceptance.

18. Architecture The system has the following main components:
Fedora repository, containing the resources, metadata, relations between the resources;
Web portal;
Search engine.

19. Architecture (cont.) Fedora Repository Web 2.0 Tools Search engine
Resources
Metadata
Relations
Class. taxonomies
Web 2.0 Tools
Search engine
Web portal
User

20. Architecture (cont.)
We have chosen Fedora as a basic repository platform.
The Fedora repository contains the learning resources (documents, presentations, videos, pictures, etc.) or references to external web resources. It also contains the metadata for the resources.

21. Architecture (cont.)
Metadata are the key for providing the needed meaning to the original resources, making them more transparent, easy to find and use.
We have chosen to use the Dublin Core (DC) metadata standard to express the metadata for learning resources as Fedora repository has full support for DC and automatically creates indexes on DC fields and supports search within DC fields.

22. Architecture (cont.)
The Fedora repository contains also the relations between the digital objects (for example the relation isMemberOf for organizing the resources in collections).
The Classification taxonomies are also stored in the repository. We have shown how OWL Ontologies (in our case Classification taxonomies) can be represented in Fedora.

23. Architecture (cont.)
The Web portal is the other main component of the system. It is an Web application (we have chosen Drupal 7 as implementation platform) that interacts with the user and implement the business logic of system. It communicates with the repository through the web services exposed by Fedora (Fedora API).
The Web portal also communicates with Web 2.0 tools (YouTube, Flickr, FaceBook, Twitter, Google+, etc.) using corresponding APIs.

24. Architecture (cont.)
We use Apache Solr search server for the Serch engine of the system. Its major features include full-text search, hit highlighting, faceted search, dynamic clustering, database integration, and rich document (e.g., Word, PDF) handling.
Whenever a resource is added to the Fedora repository the metadata for the resource is indexed by the search engine. The Web portal queries the Solr search server through the Solr web services APIs.

25. Conclusion
We have presented an advanced digital repository for learning resources that will encourage the discovery, exchange and reuse of learning resources.
The system is under active development. We have incorporated our experience in several EC funded project in this domain and have added new features and innovations.