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CGMES Background

If you're new to the power-systems domain, the acronyms behind OpenCGMES — CIM, CGMES, RDFS, SHACL, SPARQL — can be a lot at once. This page is a short primer that ties them together: what each is, how they relate, and where CIMXML files fit in. The product docs assume this background; come back here whenever a term is unfamiliar.

CIM (IEC 61970)​

The Common Information Model (CIM) is an international standard (the IEC 61970 / 61968 / 62325 series) that defines a shared vocabulary for describing electrical power networks: substations, transformers, AC line segments, breakers, measurements, and how they connect. CIM is defined as an object model (originally in UML), and its classes and properties are exported as machine-readable ontologies — the building blocks everything else in this ecosystem references.

A CIM term looks like cim:ACLineSegment (a class) or cim:ACLineSegment.r (a property — resistance of that line segment), where cim: expands to a versioned namespace IRI.

CGMES (ENTSO-E grid model exchange)​

The Common Grid Model Exchange Standard (CGMES) is ENTSO-E's profile of CIM, created so European Transmission System Operators can exchange grid models reliably. CGMES doesn't reinvent CIM — it constrains and packages it into a set of profiles, each covering one concern of a model:

  • EQ — Equipment (the network's physical elements)
  • TP — Topology (how nodes connect)
  • SSH — Steady State Hypothesis (operating set-points)
  • SV — State Variables (a computed network state)
  • …and several others (diagram layout, geographical location, dynamics, etc.)

Each profile is published as an RDFS schema file that says which classes and properties are valid in that profile. A complete grid model is a set of instance files, one per profile, that reference each other.

RDF, RDFS, SHACL, SPARQL — and how they relate​

CGMES is expressed in the RDF (Resource Description Framework) data model: everything is a set of triples (subject – predicate – object). On top of RDF sit three W3C technologies you'll meet constantly:

TechnologyWhat it isRole in CGMES
RDFS (RDF Schema)A vocabulary-definition language — declares classes, properties, rdfs:domain, rdfs:range, rdfs:subClassOfHow each CGMES profile describes its valid terms (the schema)
SHACL (Shapes Constraint Language)A constraint language — declares shapes that data must satisfy (cardinalities, value types, target classes)How CGMES expresses validation rules over instance data
SPARQLThe query (and update) language for RDFHow you ask questions of, or transform, CGMES data

The relationship in one sentence: RDFS profiles define the vocabulary, instance data uses that vocabulary, SHACL constrains the instance data, and SPARQL queries it. OpenCGMES's CIMVocabCheck checks your SPARQL and SHACL against the RDFS profiles statically — confirming your queries and shapes use real, correctly-applied CIM terms — without needing any instance data.

How CIMXML carries instance data​

A grid model's actual data — the specific substations, lines, and set-points — is exchanged as CIMXML files, an RDF/XML serialization standardised by IEC 61970-552. A CIMXML file is one of two kinds:

  • FullModel — a complete snapshot of a profile's data.
  • DifferenceModel — a delta (forward/reverse differences) to apply to a base model.

Each file carries a model header listing the profiles it conforms to and its dependencies on other model parts. OpenCGMES's CIMXML library parses these files into Apache Jena RDF graphs, resolving CIM datatypes from the registered profiles and normalising CIM UUIDs.

CIM version table​

The CIM namespace IRI in a file tells you which CIM version it uses. CIMXML supports the three current generations:

CIM versionNamespace IRI
CIM 16http://iec.ch/TC57/2013/CIM-schema-cim16#
CIM 17http://iec.ch/TC57/CIM100#
CIM 18https://cim.ucaiug.io/ns#
CGMES generation ↔ CIM version

CGMES 2.4.15 is built on CIM 16 (…CIM-schema-cim16#), while CGMES 3.0 is built on CIM 100 (http://iec.ch/TC57/CIM100#). OpenCGMES's integration tests exercise both generations — see Testing.

External references​