Title:Structured Commons Model Overview
Last modified:2014-06-15 20:30:48 UTC (Sun, 15 June 2014)
Author:Raphael ‘kena’ Poss
Source:scep0100.rst (fp:LoQ65pcKnP4X8NpxH-odbILKFSa6OL9tSZA4NlXEvr6Bag)


Structured Commons is an alternate model for scholars to register, disseminate, filter and preserve scientific knowledge.

Structured Commons was first described in an article presented at the TRUST workshop in 2014 [1] and a separate high-level technical report [2].

This document (SCEP0100) describes the Structured Commons model at a high-level.


The Structured Commons model is designed to decouple the manipulation of digital objects locally in computers (matters of data representation), the network of objects references (matters of citation), and the dissemination of object contents (matters of distribution).

This is done by layering abstractions:

  1. Object model and fingerprints (lowest)
  2. Citations and certificates of existence
  3. Object access and distribution

From a user’s perspective, a "published Structured Commons document" consists of these entities:

  • one document object and its associated fingerprint (level 1);
  • zero or more certificates of existence and one or more document handles for citations (level 2);
  • zero or more download handles for access (level 3).
Level 1: Object model and fingerprints

An object is the "body" of a publication, eg. a PDF file, directory containing TeX document sources, data set, etc. Objects are semantic (symbolic), defined independently from where they are observed and how they are stored (representation/syntax).

The layout of objects in a file system or a program’s memory is defined by its representation; multiple representations for the same object are possible.

Any user can futher compute the unique fingerprint from the semantic value of an object/document, using a secure hash function.

Level 2: Citations and certificates of existence

Users then refer to documents and cite documents in new work using a document handle, composed of:

  • its object fingerprint,
  • advisory metadata about the author list and document title,
  • optionally, one or more (links to) timestamped certificates of existence (CoE).

Document handles inform users of a document’s existence and, if coupled with a CoE, that the document existed no later than the certified date and time.

Level 3: Object access and distribution

To access or retrieve a document from its handle, a user contacts the data store network (DS) as follows:

  1. the user issues a request to the DS for the object fingerprint;

  2. the DS replies with one or more download handle (SCDH), a (small) text string that identifies a retrieval method;

  3. then either:

    3a. the user further interacts with the DS:

    1. issues a request to the DS for the download handle;
    2. receives download parameters from the DS;
    3. further proceeds as per step 3b below, or
    4. issues a request to the DS for the object data according to the download parameters.

    3b. the user uses a 3rd party network (eg. Bittorrent) to retrieve the document using the SCDH or download parameters.

In a first implementation, Structured Commons may reuse Bittorrent as distribution protocol, and reuse Bittorrent’s standard info-hash keys (also known as "BTIH") as SC download handles (SCDHs).

The mapping of object fingerprints to download handles must be maintained and served by the data store network. However, as download handles are small, it is expected that text databases containing this mapping will be published periodically on public channels, and that users can keep local copies of the download handles (and optionally the download parameters) over time for fast retrieval.


The reason why document handles and citations use an object fingerprint instead of a download handle directly (ie. why not make the download handle of a document its reference key for inter-work citations?) is that download handles are not durable in the very long term:

  • using an Internet URL as SCDL may break a citation when the domain name is transferred, the directory tree on the server is changed, the content management system is updated, etc. (also known as the "Link rot" problem [3])
  • using a Bittorrent BTIH as SCDL may break a citation if at some point Structured Commons users decide to switch to another mechanism/protocol than Bittorrent.

The reason why a user first queries a DS for a download hande, and the reason why the DS does not reply directly with the data for the object, is to promote location-agnosticism: that all DS in the network should be able to map fingerprints to download handles even if they do not have a local copy of the object.

The reason why retrieval and access can be separated in two steps (handle to parameters, then parameters to document) is to enable institutional organizations to track where copies of a document are stored and how to download them without serving copies of the documents themselves. This idea, taken from the Bittorrent protocol, is useful in the target application (academic publishing), to enable legal redistribution of "older" content where only direct authors and licensees have a right to redistribute copies.


[1]R. Poss, S. Altmeyer, M. Thompson, R. Jelier. Academia 2.0: removing the publisher middle-man while retaining impact. In Proc 1st ACM SIGPLAN Workshop on Reproducible Research Methodologies and New Publication Models in Computer Engineering (TRUST’14), Edinburgh, UK, June 2014. DOI:10.1145/2618137.2618139
[2]R. Poss, S. Altmeyer, M. Thompson, R. Jelier. Aca 2.0: Questions and answers. Technical report arXiV/1404.7753, May 2014.