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CORDRA - Overview
Terms of use
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Terms of use
These contents have been obtained from the ADL official Web site and edited for presentation. Please refer to the ADL Web site for additional information on terms of use.
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Important note
The CORDRA specification was originally developed within the ADL initiative. Currently, ADL does not continue this work and its website does not provide updated information on this specification. The last available on-line information by ADL on CORDRA is included in under section "Current version" below or on the left menu. Information available in the LTSO was obtained during the period of elaboration of the original specification. |
Overview
Advanced Distribute Learning Initiative
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Over the past 10 years, the Advanced Distributed Learning (ADL) Initiative’s Sharable Content Object Reference Model (SCORM®) evolved to provide a modular, object-based design approach for digital objects that solved key interoperability and reusability issues across many learning systems in industry and government. SCORM has enjoyed widespread international adoption, has become a de facto standard in many learning communities, and is supported by U.S. Department of Defense (DoD) policy. While SCORM advances the state of the art in designing and creating interoperable and reusable objects, it does not address finding and reusing objects after they have been created.
In 2003, ADL began work to solve this problem. ADL launched an investigation into the difficulties and realities of object creation, storage, and management and uncovered the limitations and problems encountered by others in related fields, such as library science, computer and network systems design, and publishing. As ADL investigated these fields and formulated high-level requirements for the learning community, it quickly found that many problems had not been solved by others and that the problem space was much more complex than it first appeared.
To address these issues, ADL set out to:- Define high-level requirements, policies, and business rules for object repositories that would be practical to implement.
- Identify and apply the most relevant technologies and specifications that could be used to define the architecture.
- Define an architecture on which necessary services could be built.
- Define an architecture that would be scalable.
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CORDRA (Content Object Repository Discovery and Registration/Resolution Architecture) is an effort to define a framework for the federation of digital collections. The framework aka “CORDRA specification” is intended to be an open, standards-based model for designing and implementing information systems including registries and repositories for the purposes of discovery, sharing and reuse of information. The CORDRA specification will describe how owners or managers of widely distributed information expressed in digital form may register the existence of that information and so enable others to find and use that information.
CORDRA is designed to be an enabling model to bridge the worlds of learning content management and delivery, and content repositories and digital libraries. CORDRA aims to identify and specify (not develop) appropriate technologies and existing interoperability standards that can be combined into a reference model used to enable a learning content infrastructure.
Corporation for National Research Initiatives and Advanced Distributed Learning Initiative collaborated to design and implement a metadata registry, known as ADL Registry, to showcase and provide a reference implementation of the CORDRA specification (launched in December 2005, the ADL Registry is the first publicly available CORDRA implementation). |
Terms of use
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These contents have been obtained from the ADL official Web site and edited for presentation. Please refer to the ADL Web site for additional information on terms of use.
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CORDRA (Content Object Repository Discovery and Registration/Resolution Architecture) is a model of how to enable the next step in the evolution of e-learning, namely, how to solve the problem of finding and reusing learning content.
Its goal is to develop a model for how to do this, using existing technology from the worlds of learning content management and delivery, content repositories, and digital libraries. CORDRA aims to identify and specify (not develop) appropriate technologies and existing interoperability standards that can be combined into a reference model that will enable learning content to be found, retrieved and re-used.
CORDRA is an architecture on which a family of services and tools can be built to support discovering and resolving digital objects for both specific and general contexts. An application of CORDRA in a particular domain involves establishing CORDRA registry services that implement a community’s policies and practices. Distributed repositories can then register objects and related metadata so that they can be discovered through search services. A CORDRA application, such as the ADL Registry, is called an “instance” of a CORDRA registry. |
Overall Model
Overall CORDRA model
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The overall CORDRA model and environment is illustrated in the diagram above. Key components of the model are:- Content Repositories: Local repositories for learning content (content objects, assets, etc.) and associated data (local catalogs, metadata, etc.).
- System Repositories: CORDRA system repositories for system data, models, registries, etc.
- Identifier System: Infrastructure for object identification, registration and resolution.
- Common Services Infrastructure: Core technical and administrative services used throughout a CORDRA implementation (authentication, rights management, rule processing, etc.).
- Applications: Application systems and interfaces (search, discovery, authoring, personalization, customization, delivery, etc.) used to manage and deliver learning content and content objects to end users.
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Layered Model
The CORDRA model is defined herein at three discrete levels:- General: The first level is a general abstract description of the CORDRA model, defined herein. It defines the structure, features and capabilities of the CORDRA model without defining how to implement it within a particular community of practice.
- Community Implementation: The second level describes a particular implementation of the CORDRA model. It specifies the actual set of data models, taxonomies, business rules, system structures, etc., applied to implement CORDRA for a particular community without specifying operations, an actual instantiation or mapping of the components to an operational infrastructure.
- Operational Instantiation: The third level is the actual instantiation of the CORDRA model within a community, defining the particular entities that will operate and provide services, binding of components to actual network names, etc.
CORDRA levels
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Object Model
The object model in CORDRA establishes the fundamental approach used to define the CORDRA model. The CORDRA model is based on one unifying premise:
Everything in CORDRA is an object, and all objects are treated and modeled in a consistent way.
The fundamental characteristics of a CORDRA object are:
* Each object has a name (usually human readable, internationalized).
* Each object has a unique, persistent, resolvable identifier.
* Each object is registered in a CORDRA repository (via its identifier).
* Each object is an element of a particular class of objects.
* Each object has an associated set of core attributes or kernel metadata (determined by its class).
* Each object may be associated with an extended set of attributes and data through relational objects.
* Each object has an associated set of management rules (determined by its class).
* Any object, and its associated information, is discoverable, subject to the governing management rules and rights of the object and of the agent involved in discovery.
CORDRA is built from a small set of CORDRA system objects, i.e., objects, their classes and their attributes that are explicitly defined in the CORDRA model and registered (with a machine-processable object specification) in the CORDRA System Registry when a CORDRA instance is created. All other objects are defined using the core models and object structure of CORDRA. |
Content Repositories
Content repositories are one of the two collections of data in the CORDRA model. Content repositories are used to store (persistent) collections of content objects. A CORDRA implementation may contain any number of distinct content repositories.
While CORDRA specifies requirements of the interfaces and use of content repositories within the overall model, CORDRA makes no requirements on the nature of the repositories--they may be personal, organizational or federated repositories--nor on the information they contain. Likewise, CORDRA does not impose particular rules on the management of a content repository (e.g., object persistence). In essence, a content repository is a black box to CORDRA. |
System Repositories
The system repositories are the second of the two collections of data in the CORDRA model. The system repositories are comprised of three logical components used to store:- a Master Content Catalog of all registered content objects and content object metadata in the CORDRA implementation.
- a registry of all CORDRA repositories in the CORDRA implementation.
- all descriptions of the CORDRA model and its implementation (in terms of CORDRA objects).
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Federated Model
There is nothing special in the general CORDRA model that is specific to ADL or any other community. All of the specific community characteristics can be expressed in the data models, policy rules and end user applications, and via the instantiation of the model on a particular system infrastructure.
Other organizations have expressed an interest in the CORDRA approach. It is reasonable to anticipate that the CORDRA model can be implemented for different organizations, each with their particular business rules, models and operations.
Multiple implementations may cause content to not be as widely available as desirable. Multiple implementations raise issues related to the design and use of CORDRA.
It appears logical to develop a federated model of CORDRA implementations, and that some of the core system objects of CORDRA should be defined and owned separately from any particular implementation. Note, separating the ownership of the core objects from a particular implementation (e.g., putting them into the CORDRA namespace) is independent of how these object are managed, (e.g., operation of the associated registries can be different from the formal owner of the objects).
The diagram below illustrates a model of federated CORDRA. There are multiple independent CORDRA implementations, each for a particular community, each with its own operational models, rules and content repositories. These implementations are then registered into the federated environment.
Federated CORDRA
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Terms of use
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These contents have been obtained from the ADL official Web site and edited for presentation. Please refer to the ADL Web site for additional information on terms of use.
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Title: CORDRA Documentation
Version: 1.0
Release Date: 2005
Status: Draft
Last available on-line information by ADL: |
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