Merge pull request #917 from mandy-chessell/code2024

Add descriptions of collection use cases

site/docs/concepts/collection.md

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 <!-- SPDX-License-Identifier: CC-BY-4.0 -->
 <!-- Copyright Contributors to the ODPi Egeria project. -->
 
 # Collections
 
-A collection is a reusable list of metadata elements.  [Assets](/concepts/asset) and other resources can be linked to a collection. The collection itself can then be added to a another collection, say for a [community](/concepts/community) or a [personal profile](/concepts/personal-profile).
+A collection is a reusable list of metadata elements.  [Assets](/concepts/asset) and other [referenceable](/concepts/referenceable) metadata elements can be linked to a collection. The collection itself can then be added to another collection, or linked to, say a [community](/concepts/community) or a [personal profile](/concepts/personal-profile).
+
+Collections have classifications to indicate how they are being used. Below are some examples of collections deployed in different scenarios.  The type definitions for collections are found in [model 0021](/types/0/0021-Collections).
+
+## Asset catalog hierarchy
+
+Some asset catalogs organize their catalogued resources in a hierarchical folder structure, where each folder represents a particular theme. This allows people to browse the entries in a systematic way.  Since the folder structure organizes similar assets together, it is easier to compare entries and pick the best one for the use case.
+
+Collections can be used to provide the folder structure.  The top of the hierarchy is typically classified with the *RootCollection* classification.  The nested collections linked underneath it are classified with the *Folder* classification.  The relationships linking the hierarchy and the assets together are of type *CollectionMembership*.
+
+![Asset Folder Structure](collections-asset-catalog.svg)
+
+## Product catalog organization
+
+[Digital products](/concepts/digital-product) offer data sets and services that have been developed for a particular purpose.  They are typically versioned and may offer the data/function in multiple formats.  
+
+Collections are used in two ways around digital products.  Each digital product is represented using a collection with the [*DigitalProduct*](/types/7/0710-Digital-Service) classification attached.  The digital products are often organized in a folder hierarchy, like the asset catalog.
+
+![Product catalog](collections-product-catalog.svg)
+
+## Home collections
+
+Home collections are used to organize elements for a particular person, team, project or community.  They are linked to the element representing the people they are supporting using the [ResourceList](/types/0/0019-More-Information) relationship.  An example of a home collection could be a favourites list.
+
+![Home collections](collections-home-collections.svg)
+
+## Work Item List
+
+[ToDos](/concepts/to-do) describe actions for people to perform.  They are attached to one or more chosen [*actors*](/types/1/0110-Actors).  Collections with the *WorkItemList* can be used to organize these *ToDos* to help prioritize the work.
+
+![Work Item List](collections-work-item-list.svg)
+
+## Results Sets
+
+Collections can be used by automated services, typically [governance services](/concepts/governance-service), to gather the results of their processing together.  Such a collection would have the *ResultsSet* classification attached to it.
+
+For example, the results set collection shown below is from a governance service that is identifying assets that should be archived (for example, by reviewing their [Retention](/types/4/0422-Governance-Action-Classifications) classification).
+
+![Service Results Sets](collections-results-set-1.svg)
+
+This next example is from a governance service that is periodically processing a saved query, building up the results set over time as new metadata is created.
+
+![Search Results Sets](collections-results-set-2.svg)
+
+## Recent Access
+
+User interfaces can keep track of the metadata elements that a particular user is working with so they can quickly access them.  Such a collection would be chained off of the individual's *Person* element using the *ResourceList* relationship.  The collection would have the *RecentAccess* classification attached.
 
+![Recent Access](collections-recent-access.svg)
 
+???+ education "Further Information on Collections"
+    The [Collection Manager OMVS](/services/omvs/collection-manager/overview) provides a specialist API for managing collections.
 
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