The Photodentro Aggregator Federated System Architecture

A powerful metadata aggregator backend, coupled with a web portal frontend
for a mobile-friendly, accessible and socially interactive user experience.

Anastasios Koutoumanos  Ph.D.
Computer Technology Insitute & Press - Diophantus

Our team

A 'digital' team for implementing and supporting
the 'digital services' of the digital school!

  • Headed by Prof. Christos Kaklamanis
  • Coordinated by Dr Elina Megalou
  • An efficient software team
    • 11 full-time, in-house developers & dev-ops
    • a team of ~10 external colleagues doing part-time work
  • A great back-office team for supporting our work, the digital services and the associated content
I'm an Engineer

The Context: Photodentro is the ...

Greek National Aggregator of Educational Content for schools.

It has been designed and developed in the framework of the
"Digital School" National Initiative of the Greek MoE

Dschool logo NSRF 2007-2013

Photodentro Aggregator

A multi-layer and service oriented architecture has been used for the Photodentro Aggregator, with the following layers:

  1. the Ingestion layer, that processes metadata from various external sources,
  2. the Collection Management Layer, that manages the collections that are to be aggregated in the Federation and provides an environment for their metadata enrichment,
  3. the Aggregation Layer, where the metadata harvesting, validation, and storing take place, and
  4. the Photodentro Web portal, that provides general services to portal users as well as access to the resources of various repositories in a uniform way.

System Architecture

The main components

  • Sources of related material
  • Repositories with learning resources
    • Photodentro instances
    • Other, compliant repositories
  • The Photodentro aggregator
  • The Photodentro portal

Photodentro Aggregator

The main components

DSpace Aggregator engine Portal frontend
  • LOM AP builder
  • Unique Identifier service
  • OAI-PMH target
  • Support services
    • Vocabulary server
    • LOM Validator
  • OAI-PMH Harvester
  • Quality Control engine
    • Link check
    • Photodentro LOM AP validation
  • Schedule management (cron)
  • Reporting
  • SOLR Indexing
  • Transformation
  • Publish
  • Layout
  • Social Features

Injestion & Collection Management

Metadata Injestion & Transformation

Photodentro uses the MINT tool (part of the Metadata Interoperability Services) for gathering metadata from external repositories as well as for facilitating the metadata mapping process.

Collection Management

Three different cases of repositories:

  • Case 1: Full support
    • Fully support the Photodentro IEEE LOM AP, and
    • Provide an OAI-PMH target, and
    • there is no need for metadata enrichment
  • Case 2: Different IEEE LOM AP or other standard (e.g. LIDO)
  • Case 3: Partial support
    • Fully support the Photodentro IEEE LOM AP and
    • Provide an OAI-PMH target, but
    • metadata enrichment is needed

Metadata preparation

A (heavily customised version of) DSpace is used to provide:

  • a Unique Identifier service
  • mapping to the Photodentro LOM Application Profile
  • an OAI-PMH target


The HANDLE system is used as the backend service
to create globally unique, persistent and independent identifiers.

Aggregator requirements

  • collect metadata records from the Photodentro ecosystem
  • enforce quality and unique identifiers
  • prepare metadata to be used by the Photodentro portal
  • link metadata against the taxonomies and terms of the Vocabulary Bank
  • facilitate smart indexing and advanced query services (Athena)
  • facilitate association of metadata with related social data and analytics

Our approach: Drupal based

The main workflow

  1. An OAI-PMH module is used as and aggregator to harvest all connected repositories.
  2. A set of curation tasks are performed
  3. Each valid metadata record is tranformed to a Drupal entity
  4. Each entity is submitted to the SOLR indexer
  5. Drupal entities enter the normal publishing workflow

Action please!

Hands on. Live!

Note: This is only for demostration purposes. System under heavy development!

Web services & tools


... and the Future


The system is currently under development

1st working version is expected by September 2014

  • Potential user base: approx. 1.5 milion, mostly members of the Greek K-12 community.
  • Everyone will be motivated to register as a member
  • Emphasis on community-oriented features
  • Responsive, finger-friendly user interface
  • Faceted search, intuitive search mechanism
  • Accessibility is facilitated (WCAG 2.0 Level AA) and expanded with speech-enabled web components
  • Architectured for scalability

The future

  • Integration of the Photodentro aggregator and portal to the other dschool components.
  • Explore the micro-sites paradigm
  • Management of social data & paradata, processing of analytics
  • Further support the Linked-Data paradigm
  • Link to more repositories, both inbound and outbound
  • ... more to come. We listen to our users!