8. Linking physical objects

Instruments and their individual configuration represent the major reference for the origin of a broad spectrum of data. As such, both become part of the Internet of Things (IoT) and therefore it is of key importance for related identification mechanisms to enable physical access to these objects in addition to their digital representations or catalogue metadata. Thus, to ultimately allow the “mapping the real world into the virtual world”.[1] This kind of access is essential to reproduce science as it allows us to compare experimental setup and to repeat analyses.

The most trivial but failsafe method to link physical objects with their virtual representation would be to permanently label an instrument by writing or engraving its PID onto it or its container along with its inventory number and serial number. Because space for labels is limited on smaller sensors, modern QR tags or barcodes may be more convenient as they offer the possibility to encode any identifying information in a machine readable way. A recommended way would be to use QR codes to embed a PID’s actionable URIs (Figure 8.1). Ideally such a QR badge additionally displays the PID as well as the inventory number and serial number in a human readable way. Some QR code generators now allow users to integrate images like organisation logos or track scanning activity such as the GPS position when the label is scanned.

In case neither labelling of physical objects with barcodes or PID strings is possible, linking of instruments with their digital representation can be maintained by providing appropriate metadata records. For instruments such linking can be achieved by capturing identifiers which uniquely identify an instrument such as serial number or inventory number.

While PIDINST schema metadata does not provide explicit fields for serial numbers or inventory numbers, it currently offers a generic way to capture any kind of identifier which can be used for this purpose. AlternateIdentifier can be used to record any identifier string and alternateIdentifierType to specify an identifier type (Snippet 8.1). PIDINST schema recommends the use of the terms serialNumber and inventoryNumber. There is on-going discussion regarding the use of explicit fields for these properties in PIDINST.

Figure 8.1 An example of a webpage QR code that includes an organisation logo and re-directs the scanner to the PID URL (http://hdl.handle.net/21.T11998/0000-001A-3905-F).

Snippet 8.1 An instrument serial number expressed in XML

  <AlternateIdentifiers>
     <AlternateIdentifier alternateIdentifierType="serialNumber"">7351-349l-mn24-019f</AlternateIdentifier>
  </AlternateIdentifiers>

Besides storing e.g. serial numbers in PIDINST schema metadata, it is highly recommended to store the instrument PID within an institutional sensor management or inventory system immediately after PID registration. This ensures the maintenance of links between physical objects and their virtual representation at both endpoints, the institutional sensor management system as well as the PID registry, and will ensure the persistence of object linking in case of failures on either side.

[1]	Atzori, Luigi & Iera, Antonio & Morabito, Giacomo. (2010). The Internet of Things: A Survey. Computer Networks. 2787-2805. 10.1016/j.comnet.2010.05.010.