Examples of lightweight ontologies include associative network and multilingual classifications but the term is not used consistently.
Following the approach described in [1] and exploiting dedicated Natural language processing (NLP) techniques tuned to short phrases (for instance, as described in [2]), each node label can be translated into an unambiguous formal expression, i.e. into a propositional Description Logic (DL) expression.
As a consequence, the backbone structure of a lightweight ontology is represented by subsumption relations between nodes.
[3] and [4] show how lightweight ontologies can be used to automate important tasks, in particular to favor interoperability among different knowledge organization systems.
[5] is an example of how a lightweight ontology can be used selectively for information exchange and service interoperability in time-critical decision support systems.