Svenska Kraftnät’s semantic framework is based on a modular structure in which the base ontology, BASE, serves as a common foundation. By gathering general and domain-independent concepts in BASE, the more specialised Electricity Market Data Ontology (EMDO) can focus on electricity market data while following a shared approach to modelling information.

This makes it possible to describe published datasets in a consistent and machine-readable way. Instead of publishing data solely as columns and values, the information is linked to clearly defined concepts, properties, code lists, and relationships. This makes it easier for both humans and systems to understand what the data actually represents.

The goal is to facilitate interpretation, combination, and reuse of data from Svenska Kraftnät’s Data Service.

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Purpose and usage

The ontologies have been developed to:

• establish a common semantic structure for published datasets
• enable machine-readable interpretation of published data
• facilitate links between different data sources
• support interoperability with national and international systems
• clarify the concepts, units, and code lists used
• make it easier for developers, analysts, and other data consumers to use the data correctly

To simplify the connection between ontologies and actual datasets, column names are documented as alternative labels on classes and properties. However, the meaning itself is defined in the ontology through classes, relationships, and links to code lists and external concepts.

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Architecture and structure

The framework consists of two main parts:

• BASE – common base ontology
• EMDO – electricity market data

BASE contains reusable building blocks, while EMDO specialises these for the electricity market domain. In addition, code lists complement the ontologies by defining valid data values.

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1. Base ontology (BASE)

https://data.svk.se/ontology/base

A foundational ontology providing reusable and domain-independent concepts and data structures used across Svenska Kraftnät’s domain ontologies. The ontology defines core entities such as time series values, observations, forecasts, units of measure, currencies, geographical areas, and countries, along with associated properties for describing values, temporal validity, and units. It also establishes modelling patterns for linking data to controlled vocabularies via code lists. The ontology supports semantic consistency, interoperability, and reuse of shared definitions across systems, datasets, and electricity market applications.

BASE contains general concepts that can be used across many types of datasets, particularly those with time-dependent values.

Time series values

The class base:TimeSeriesValue is used as an overarching structure for values linked to time, such as observations and forecasts.

Observations and forecasts

BASE distinguishes between different types of time-based values:

• base:Observation – measured or calculated values published as actual results
• base:Forecast – future-oriented estimates

This makes it clear whether a value describes an actual outcome or a prediction.

Units of measure

A general model for units exists through base:UnitOfMeasure and specialisations such as:

• power (PowerUnit)
• energy (EnergyUnit)
• frequency (FrequencyUnit)
• currency (CurrencyUnit)

This separates the value itself from the unit in which it is expressed.

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2. Electricity Market Data Ontology (EMDO)

https://data.svk.se/ontology/emdo

Description of EMDO

EMDO builds on BASE and describes concepts, properties, and data types related to electricity market data.

It is used to model data such as:

• physical flows
• transmission capacity
• bids and imbalances
• reserve markets
• bidding zones and settlement

EMDO defines more specific types of observations and forecasts, still based on BASE but tailored to the electricity market.

Examples of concepts:

• emdo:BiddingZone
• emdo:SynchronousArea

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Code lists

Code lists, also known as SKOS concept schemes, are used to define the valid values for certain properties, for example:

• countries
• bidding zones
• production types
• currencies

They are linked to properties via base:hasCodeList. This is primarily documentation; validation itself is handled separately, for example using SHACL. Where relevant, code list concepts can be linked to external standard concepts, such as QUDT units and currencies, using skos:exactMatch.

Code lists (concept schemes) for Svenska Kraftnät:

• Balancing service types
• Reserve direction
• Auction rounds
• Bidding zones
• Country codes
• Dominant regulation direction
• Forecast horizons
• Interconnectors
• Production categories
• Production types
• Trade action direction
• Units of measure

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Semantics and inference

The ontologies enable systems to understand how datasets, concepts, and properties are related.

For example, specific classes in EMDO can be understood as specialisations of more general concepts in BASE. An electricity market observation can therefore be described both as a domain-specific concept and as a general observation according to the shared structure in BASE.

The framework thus supports basic semantic inference through class hierarchies, relationships, and links to code lists and external concepts. However, it is not currently designed as a comprehensive rule or validation system. The primary goal is to provide a clear, reusable, and machine-readable semantic structure for published open data.

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Versioning

Each ontology has both a stable base IRI and a version IRI:

BASE

• Latest: https://data.svk.se/ontology/base
• Version: https://data.svk.se/ontology/base/v1.0.0/

EMDO

• Latest: https://data.svk.se/ontology/emdo
• Version: https://data.svk.se/ontology/emdo/v1.0.0/

The base IRI serves as the stable identifier, while the version IRI allows specific versions to be distinguished over time.

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Target audience

The combined ontology framework is intended for data consumers, analysts, system developers, information architects, and other stakeholders who want to understand, combine, or reuse Svenska Kraftnät’s open data.

It can be used to:

• interpret published datasets machine-readably
• build semantic integrations
• combine data from multiple domains
• create knowledge graphs
• analyse time series data
• understand the relationship between the physical structure of the power system and electricity market processes

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Summary

By publishing these ontologies openly, Svenska Kraftnät creates better opportunities for reuse, transparency, and interoperability.

This means that their data can not only be read, but also understood and linked with other data sources in a structured and meaningful way.