Wednesday, January 8, 2020

A closer look at the Nomisma monogram data model

After the launch of more than 1,200 monograms that appear on the coinage of Alexander the Great as part of the PELLA project, I have made some updates to the data maintenance framework that underlies These changes enable monogram datasets to be added/removed via revised SPARQL/Update queries that incorporate CIDOC CRM properties to link to image files and the W3C PROV ontology for data provenance (similar to the model we already implement for Nomisma concept URIs). Note that the PROV ontology is not used for data provenance for coin type corpora or hoard databases, although this is something we should consider implementing at some point.

Introduction to the Monogram/Symbol data model

Monograms published to the web follow a similar pattern to other SKOS concepts in our ecosystem. The RDF class is nmo:Monogram from the Nomisma ontology. Our ontology will be updated soon to give nmo:Monogram a superclass of CIDOC CRM's E37_Mark. Any other symbol that appears on a coin (which can be letters used as control marks or mint marks and pictographic symbols, such as "torch" or "ram's head") are also E37_Marks. The definition of a Mark is as follows:

This class comprises symbols, signs, signatures or short texts applied to instances of E24 Physical Man-Made Thing by arbitrary techniques in order to indicate the creator, owner, dedications, purpose, etc.

All symbols are inherently concepts and have one required skos:prefLabel and one skos:definition in English. Like other concepts, there might be a Field of Numismatics (dcterms:isPartOf) or Bibliographic reference (dcterms:source) pointing to Nomisma URIs.

Since all symbols are E37_Marks (directly or indirectly), we are able to use some other CIDOC CRM properties. The crm:P106_is_composed_of property points to constituent letters or symbols. Typically, this is letter, but we have at least a few examples of RIC 10 monograms that are composed of letters and Christograms. When we publish a new edition of these monograms into OCRE, we are going to create the Christogram URIs in a new /symbol/ namespace in Using property paths, it will be possible to execute a SPARQL query for any monogram that includes a Greek rho, regardless of whether this letter appears directly in the monogram or is part of a monogram that is contained within a monogram.

  a nmo:Monogram, skos:Concept ;
    <> ;
  void:inDataset <ttp://> ;
  crm:P106_is_composed_of "Κ", "Υ", "Ο" ;
  skos:prefLabel "Price Monogram 1000"@en ;
  skos:definition "Monogram 1000 from M.J. Price, Coinage in the Name of Alexander the 
    Great and Philip Arrhidaeus: A British Museum Catalogue. The monogram contains 
    Κ, Υ, and Ο as identified by Peter van Alfen."@en ;
  dc:source <> ;
  dc:isPartOf <> ;
    <> .

We link to one or more digital image files representing an idealized view of the monogram or symbol with the property, crm:P165i_is_incorporated_in. At the recommendation of the CRM SIG, this digital image (an SVG file: see Github for the full repository of monograms SVGs) bears a crmdig:D1_Digital_Object class and some additional triples about the license (CC Public Domain Mark), the ORCID of the graphic artist who drew them (Mark Pyzyk), and the mime-type as dcterms:format.

  a crmdig:D1_Digital_Object> ;
  dc:format "image/svg+xml" ;
  dc:creator <> ;
  dc:license <> .

Like Nomisma concepts, these monograms have some provenance metadata, linking them to Peter van Alfen's Nomisma editor URI as the contributor (of the constituent letters) and a link to a source Google Spreadsheet. These monograms were imported into PELLA through a new symbol spreadsheet import functionality implemented in the Numishare platform itself. It operates much like the spreadsheet import in Nomisma, parsing the spreadsheet and transforming rows into RDF files that get stored in Numishare's eXist-db XML database.

While there is a basic interface built into PELLA (and other monogram corpora when they get published in Numishare) to query by constituent letter based on XQuery of the XML database, ultimately, I plan to implement a unified interface for this sort of query directly in which will be based, instead, on SPARQL (see this basic example query). This will open the door to querying across many type corpora (Seleucid and Ptolemaic coinage combined), as well as exploit the relationships between letters, monogram URIs, and coin types that have been linked to those monogram URIs, paving the way to extract lists of mints, authorities, etc. connected to certain letters, and sort these by chronology or other categories. This is merely the tip of the iceberg in new forms of query of numismatic data that were never previously possible at this scale, made possible by Linked Open Data methodologies.