DCC

A Ruby library for parsing, validating, converting, signing, and building PTB Digital Calibration Certificates (DCC) and D-SI quantity documents.

Built on top of the lutaml-model framework, dcc provides a fully typed Ruby object representation of both the DCC and D-SI XML schemas, with per-major-version class hierarchies mirroring the approach used by the mml gem for MathML.

What is a Digital Calibration Certificate?

A Digital Calibration Certificate (DCC) is an XML-based, machine-readable calibration certificate developed by Germany’s national metrology institute, the Physikalisch-Technische Bundesanstalt (PTB). It is designed to replace traditional paper-based calibration certificates with a format that both humans and machines can process automatically.

A DCC document contains three primary sections:

• Administrative data — identifies the calibration laboratory, the customer, the calibrated item(s), responsible persons, performance dates, and any statements about traceability or conformity.

• Measurement results — the actual calibration data: measured values, uncertainties, units, environmental conditions, and the methods/equipment used. Each measurement quantity is expressed using the D-SI format.

• Document — optional attached files (PDF reports, spreadsheets, images) embedded as base64 binary data.

The certificate can be digitally signed using W3C XMLDSig to guarantee authenticity and integrity.

What is D-SI?

D-SI (Digital System of Units) is a companion XML format for expressing SI-based measurement quantities with full uncertainty information. A D-SI quantity carries the value, unit (in siunitx notation), and an uncertainty model (standard, expanded with coverage factor k, or coverage interval).

For example, a resistance measurement of 100.0225 Ω ± 0.003 Ω (k=2):

<si:real>
  <si:value>100.0225</si:value>
  <si:unit>\ohm</si:unit>
  <si:expandedMU>
    <si:valueExpandedMU>0.003</si:valueExpandedMU>
    <si:coverageFactor>2</si:coverageFactor>
    <si:coverageProbability>0.95</si:coverageProbability>
  </si:expandedMU>
</si:real>

D-SI also supports complex quantities, constants, lists (both verbose and compact XML-list forms), hybrid multi-unit representations, covariance matrices, and coverage regions for multivariate uncertainties.

Highlights

• Fully typed object model for DCC v2.x and v3.x (no more XPath over lxml)

• Fully typed object model for D-SI v1.x and v2.x

• Lossless round-trip XML fidelity (parsing then serializing is byte-equivalent after canonicalization via moxml)

• Pure-Ruby Schematron engine implementing the 14 PTB Schematron patterns (no Java/Saxon-HE dependency)

• XSD validation against all 12 bundled DCC schema versions

• JSON / YAML / CSV / HTML converters

• MathML formula support via the mml gem (typed model, not raw strings)

• XMLDSig signature signing and verification via moxml native Signature

• Programmatic DCC builder DSL for issuing new certificates

• Structural diff of two certificates

• Version migration helpers

• Thor-based CLI with validate, convert, extract, signature, transform, inspect, diff, and issue commands

Quick start

Install the gem:

$ gem install dcc

Parse a certificate:

require "dcc"

dcc = Dcc.parse(File.read("certificate.xml"))
dcc.administrative_data.core_data.unique_identifier
dcc.measurement_results.measurement_result.first.results.result.first.data.first.quantity.first.name

Validate:

result = Dcc::Validate::Xsd.call(File.read("certificate.xml"), version: "3.3.0")
result.ok? # => true

Building a new DCC

Use the builder DSL to issue a certificate programmatically:

require "dcc"

dcc = Dcc.build(version: 3) do
  administrative_data do
    core_data do
      unique_identifier "urn:uuid:00000000-0000-0000-0000-000000000001"
      country_code "DE"
      used_lang "en"
      mandatory_lang "en"
      begin_performance_date Date.today
      end_performance_date Date.today
    end

    items do
      item(model: "Pt100", manufacturer: "ACME Sensors") do
        name { content lang: "en", value: "Resistance Thermometer" }
      end
    end

    calibration_laboratory do
      calibration_laboratory_code "PTB-123"
      contact do
        name { content lang: "en", value: "Calibration Lab" }
        e_mail "lab@example.org"
        location do
          city "Berlin"
          country_code "DE"
        end
      end
    end

    resp_persons do
      resp_person do
        person do
          name { content lang: "en", value: "Dr. Jane Doe" }
          e_mail "jane@example.org"
        end
        main_signer true
      end
    end

    customer do
      name { content lang: "en", value: "Acme Corp" }
    end
  end

  measurement_results do
    measurement_result do
      name { content lang: "en", value: "Resistance at 0 °C" }
      results do
        result do
          name { content lang: "en", value: "R(0 °C)" }
          data do
            quantity do
              name { content lang: "en", value: "Measured resistance" }
              # D-SI quantity element (si:real) is wired via the typed model
            end
          end
        end
      end
    end
  end
end

puts dcc.to_xml

Signing a DCC

Sign with an X.509 certificate and RSA private key:

require "dcc"

cert_pem = File.read("cert.pem")
key_pem  = File.read("cert.key")

signed_xml = Dcc::Signature::Signer.call(
  File.read("certificate.xml"),
  cert_pem: cert_pem,
  key_pem: key_pem,
)

File.write("certificate_signed.xml", signed_xml)

Verify a signed certificate:

result = Dcc::Signature::Verifier.call(
  File.read("certificate_signed.xml"),
  ca_cert_pem: cert_pem,
)
result.valid? # => true

CLI

$ dcc inspect certificate.xml
$ dcc validate all certificate.xml
$ dcc convert json certificate.xml -o certificate.json
$ dcc extract files certificate.xml
$ dcc signature sign cert.pem key.pem certificate.xml -o signed.xml
$ dcc signature verify cert.pem signed.xml
$ dcc diff a.xml b.xml

Status

This gem is under active development. See TODO.complete/ for the current work breakdown.

License

MIT — see LICENSE.