The ISO AggregateInformation object provides a powerful mechanism for grouping multiple metadata records into sets based on a number of relationships described by the AssociationType and InitiativeTypeCodes. Note that the sets are identified by MD_Identifiers which suggests that they could have metadata records of their own.
Scientific Earth Drilling Information Service
: This metadata for a core from an ocean drill hole includes a section called "Relations" which provides access to groups of information from a single hole or to groups of holes from a single expedition.
International Ocean Drilling Program (IODP)
See examples at http://sedis.iodp.org/front_content.php?idart=96&index=datasets&identifier=oai%3Apangaea.de%3Adoi%3A10.1594%2FPANGAEA.206854
Using aggregateInfo for Programs/Projects
Many datasets are collected as part of projects or programs. The aggregateInfo object allows you to identify those. They can be identified as largerWorkCitations or crossReferences.