4.1 The archived data
An archive must be able to store any data:
Most archive systems give access to the data via search. Usually, we search on structured data. Either the data is persisted aggregated, then the search only filters the relevant records to the user, or the search does the aggregation on the fly.
Some archives also support search through unstructured data (like PDF documents), but this far less powerful, so it's common to archive unstructured data with its metadata stored in a structured form.