  Representing snippets of information abstractly is a task that needs to be
performed for various purposes, such as database view specification and the
first stage in the natural language generation pipeline for generative AI from
structured input, i.e., the content selection stage to determine what needs to
be verbalised. For the Abstract Wikipedia project, requirements analysis
revealed that such an abstract representation requires multilingual modelling,
content selection covering declarative content and functions, and both classes
and instances. There is no modelling language that meets either of the three
features, let alone a combination. Following a rigorous language design process
inclusive of broad stakeholder consultation, we created CoSMo, a novel {\sc
Co}ntent {\sc S}election {\sc Mo}deling language that meets these and other
requirements so that it may be useful both in Abstract Wikipedia as well as
other contexts. We describe the design process, rationale and choices, the
specification, and preliminary evaluation of the language.
