extensionOpeningYear

Given a predicate that represents a relationship or action between entities, generate a one-sentence description explaining its meaning.  
# Instructions
Focus on describing the relationship, not the entities themselves. 
# Response Format
Begin the description with \' Indicates...\'

Predicate: extensionOpeningYear

Indicates the year in which an extension to an existing entity (such as a building, line, or service) was officially opened or put into operation.