Learning Outcomes

• Understand the purpose of a repository
• Learn what Fedora can do for you
• Understand the key capabilities of the software

Course Outline

Introduction to Fedora 4

What is a Repository?

• Secure software that stores, preserves, and provides access to digital materials
• Supports complex semantic relationships between objects both within and outside the repository
• Supports millions of objects, both large and small
• Capable of interoperating with other applications and services

Fedora 4 Guiding Principles

• Improved performance, enhanced vertical and horizontal scalability
• More flexible storage options
• Features to accommodate research data management
• Better capabilities for participating in the world of linked open data
• An improved platform for developers—one that is easier to work with and which will attract a larger core of developers.

Exposing and Connecting Content with Fedora 4

• Flexible, extensible object modelling
• Atomic objects with semantic connections using standard ontologies
• RDF-based metadata using Linked Data
• RESTful API with native RDF response format

Core Components

Durable Storage

One of the core components of Fedora 4 is its long-term storage and preservation capability. A number of features support this capability; they have been grouped here under the notion of Durable Storage.

Fixity

• Over time, digital objects can become corrupt and unusable by suffering from bit rot and other digital preservation dangers
• Fixity checks help preserve digital objects by verifying their integrity using techniques such as checksumming
• On content ingest, Fedora can verify a user-provided checksum against the calculated value
• A checksum can be recalculated and compared at any time via a REST-API request 

Backup and Restore

• A full backup, including all binaries as well as a compact serialization of all containers, can be performed at any time
• A full restore from a repository backup can be performed at any time

Export and Import

• A specific Fedora resource, its children resources, and associated binaries can be exported
  • The serialization of the Fedora resource is more portable than the compact form found in the backup/restore feature
  • Exported resources are serialized in a standard JCR/XML format
• An exported resource or hierarchy of resources can be imported at any time

Versioning

• Versions can be created across the entire repository or on particular API calls.
• A previous version can be restored via the REST-API.

Data Modelling

Resources

• Both containers and binaries are represented as resources.
• Container nodes can have both containers and binaries as children.
• The tree structure allows for inheritance of things like security policies.

Properties

• Resources have a number of properties, which are expressed as RDF triples.
  • The resource itself is the implicit subject of each triple.
• Properties can be RDF literals (e.g. dc:title) or they can express relationships both internal and external to the repository.
• Any number of RDF namespaces can be defined and used.

Content Models

• Content can be modelled using RDF properties
• Properties can have either literals or URIs as their objects
• Resources can have any number of properties using any number of namespaces

Linked Data

• Fedora 4 is compliant with the LDP 1.0 spec.
• Metadata can be represented as RDF triples that point to resources outside the repository.
• Many possibilities for exposing, importing, sharing resources with other web applications.

User Interface

Administrative Console

Tour of the HTML administrative interface.

External Components

Camel

Indexing

• Indexing repository content for external applications can be accomplished by using the Camel component.
• The Camel component receives JMS messages on repository updates and relays these messages to one or more external applications.
• Repository content can be optionally assigned the rdf:type property "Indexable" in order to be filtered from non-indexable content (any predicate will do)

Triplestore

• An external triplestore can be used to index the RDF triples of content managed by Fedora.
• Any triplestore that supports SPARQL-update can be used; Fuseki and Sesame have been tested.

External Search

• An external search application can be used to perform more complex search queries on repository content.
• Any search application that supports JSON-based updates can be used; Solr has been tested.

Authorization

• Authentication (not to be confused with authorization) is assumed to take place in a layer above the application.
• The authorization framework provides a plug-in point within the repository that calls out to an optional authorization enforcement module.
• Currently, two authorization implementations exist.

Role-based Authorization

• Basic authorization compares the user's role(s) with an Access Control List (ACL) defined on a Fedora resource.
• ACLs can be inherited; if a given resource does not have an associated ACL, Fedora will examine parent resources until it finds one.

XACML Authorization

• XACML policies can provide much more complex and granular authorization.
• A default policy must be defined for the repository, and each resource can override the default with another policy.
• A XACML policy referenced by a resource will also apply to all the resource's children, unless they define their own XACML policies that override the parent policy.

Audit Service

• Maintains a history of events for each repository resource
• Both internal repository events and events from exterior sources can be recorded
• Uses the existing event system, Camel component, and external triplestore

OAI Provider

• Implements Open Archives Protocol Version 2.0 using Fedora 4 as the backend.
• Exposes an endpoint at /oai which accepts OAI conforming HTTP requests.
• Supports oai_dc out if the box, but users are able to add their own metadata format definitions to oai.xml.

Performance

Transactions

• Multiple actions can be bundled together into a single repository event (transaction).
• Transactions offer performance benefits by cutting down on the number of times data is written to the repository filesystem (which tends to be the slowest action).

Clustering

• Two or more Fedora instances can be configured to work together in a cluster.
• Fedora 4 currently supports clustering for high-availability use cases.
  • A load balancer can be setup in front of two or more Fedora instances to evenly distribute read requests across each instance.
  • If one Fedora instance in the cluster goes down, read requests can be directed to the other instance.
  • Ingests are replicated across all instances in the cluster.