Subcollection

Subcollection is a term used across disciplines to describe a portion of a larger collection. In mathematics, a collection can be a set or a family of objects. A subcollection is a subset formed by selecting elements that satisfy a criterion, or by listing specific elements from the original collection. Depending on context, a subcollection may be equal to the whole collection or a proper part of it. Different disciplines may prefer different terminology, but the core idea is that every element of a subcollection is also an element of the original collection.

In set theory and related fields, a subcollection often corresponds to a subfamily or a subset of a family of objects. When the original collection is a set, the subcollection is a subset; when the collection is a broader construct such as a class or a family, the term subcollection emphasizes the grouping of elements by a common property rather than set-theoretic size alone.

In computing and data management, the term subcollection is used in hierarchical data models. For example, in Google Cloud Firestore, a subcollection is a collection that exists under a specific document, enabling nested structures. Each document can have zero or more subcollections, each with its own documents and fields. The concept helps organize data by grouping related items under a common parent.

In libraries, museums, and archives, subcollections refer to subsets created from a larger collection according to subject, author, date, format, or other criteria. Subcollections aid organization, retrieval, and analysis without duplicating original items.