Further definitions for collections

13 Jun 2016

Dear all,
I've taken another shot at extending the definitions - in view of the
discussion about collection metadata and capabilities. Let me know what
you think - I want to use these to extend the current definitions in the
draft doc later on.
Every individual *collection* is a 2-tuple of an identifier and
collection state.
--> The identifier is part of a collection to allow users to define
multiple collections that are identical with regards to their membership
and general behaviour (operations, metadata etc.).
The *collection state* is a 3-tuple of collection membership, collection
capabilities and collection description.
The *collection capabilities* fully comprises the set of actions that
are supported by it. Actions may or may not affect collection state.
--> An external agent may provide more actions than are in a
collection's capabilities, e.g. more sophisticated composite actions or
actions across multiple collections.
--> An agent submits a capability request to a collection to retrieve
the action set.
*Collection metadata* is a super category that covers informative
elements of collection membership, capabilities and description. All of
the collection description is metadata.
--> An example for membership metadata is the collection size; an
example for capability metadata is the currently valid list of supported
actions; examples for description metadata include the purpose for which
the collection was created, thematic criteria for membership, citation
and licensing information.
*Collection membership* is a 3-tuple of a finite set of item identifiers
S, a function F mapping from S to item metadata elements and collection
membership metadata M. The set S may be explicitly defined (naming all
item identifiers) or implicitly defined (by a generation rule). The
domain of set S consists of all collections and all collection items,
thus collections can be members of other collections, as long as the
recursion rule is not violated. There may also be an order defined on S,
whose definition must then be part of the collection membership metadata.
--> The function F need not be injective: Multiple items can be related
to the same metadata.
--> Recursion rule: The collection membership may not be recursive: S
may not contain the collection itself or any collection that it is part of.
Best, Tobias
Tobias Weigel
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