The NBC+ Search Platform

As many wonder what the National Library’s Catalogue (NBC) actually is, I try to explain it here from a technical perspective.

National Catalogue

The majority of the Dutch public libraries use a central catalogue of publications and only register what they have in stock locally. These registrations refer to the central catalogue and only add limited information which is unique for that library.

But many libraries also offer extra publications not present in the national catalogue. For example music albums, newspapers, consumer test reports, event guides, special interest publications and so on. This is where the Search Platform comes in.

The Search Platform

The Search Platform makes all these publications from all these sources available through a unified Application Programming Interface (API). An API means: not for humans, but for computers.  So it is possible to use the vast amount of library related data in any conceivable way to create end-user applications.

Here is a short list of what Search Platform makes accessible:

  1. Concise and unified metadata description of all publications
  2. Detailed information about organizations (libraries, publishers, musea, etc)
  3. Unified typology of all things inside the Platform: music, books, e-books, people, video, software, games, articles, and so on.
  4. Details from leading Author thesauri, classifications etc.
  5. Both unified and Raw (meta) data of everything.

Here is a short list of what functionality the API has:

  1. Integrated topic search with autocomplete and term suggestions.
  2. Static and dynamic ranking.
  3. Object resolving.
  4. Structured queries.
  5. Harvesting.
  6. Icons and thumbnails.
  7. Get-It services for: loan, download, reserve, etc.

Semantic Data

The Search Platform works with Semantic Data.  Instead of boosting all the hyped technical details of RDF and LOD, we just list what it actually achieves for API users:

  1. Uniform data representation regardless of how you access it.
  2. Clear and unambiguous relations between objects.
  3. Open and detailed data directly linking to the source without information loss.
  4. Multi-structured: pick your favorites from many ontologies.
  5. Easy integration with other tools and techniques.


The Search Platform features two key innovations:

  1. Late Integration. It keeps separate indexes and integrates results on the fly.  This allows for easier and more specific maintenance of the indexes while integration happens in milliseconds. This required a technical innovation. Read more about it in “Reducing Index Maintenance Costs…” and in the more technical post here.
  2. It crosses the chasm between statistical information retrieval and linked data by employing both technologies and combining them in a clever way in the API.  As for the reason and how, please bear with me, as the next post will be about this exact topic.


The Search Platform is now in production. The Public Library of Amsterdam uses it for all its branches.  It combines the National Catalogue with, among others, the music collection of and local events from  Late Integration makes sure maintaining the indexes is very easy.

Other features (ready or under development) are:

  1. Dynamic static rank: a separate ranking query, reweighs results according to static ranks maintained in a separate index.  Such ranks include at this moment: age, , holdings, sources and types.
  2. Uploading and using more ontologies so that more content becomes navigable through them.
  3. Extensive availability services providing detailed information on how to get each object, how, where and under what conditions.

Especially the last point is an interesting added value of the Search Platform.  No matter what one finds, one always wants to click-through to see more. In the library and cultural heritage domain, that involves almost always more than just providing a link.  The platform uses a both generalized and specialized implementation of the Availability Information working draft (DAIA).  A next blog post will offer more details on the architecture and application of DAIA.


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