Purpose: POWER is an ontology of political processes and entities. It is designed for tracking politicians, political organizations and elections, both in mainstream and social media. The aim of this paper is to propose a data model to describe political agents and their relations over time. Design/methodology/approach: The authors propose a data model to describe political agents (politicians, political institutions and political associations) and their relations over time. The model is formalized as an ontology using the RDF format and the population is performed in two steps. First, a bootstrap process loads data collected from authoritative sources. Then, the ontology is enriched with alternative media names extracted from the web. Findings: The ontology is published as a public resource following the guidelines of linked data and semantic web standards can be accessed via SPARQL endpoint. Originality/value: The authors have developed an ontology for the political domain tailored to aid in the tasks of named entity recognition and resolution. It represents the complexity and dynamic nature of relations between political agents (politicians, political associations and political institutions) over time. (Contains 2 tables, 5 figures, and 13 notes.)