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MAP Holon Descriptors
HolonDescriptors include a TypeHeader that stores fields that are common to all MAP Descriptors. They also include a property_descriptor_map
that specifies the set of properties provided by this Holon Type. See PropertyDescriptorMap.
Currently open enhancement requests will be adding Constraints and Access Paths (described below). In the future, an AffordanceMap will be added to specify the set of Affordances offered by this Holon type.
Within a DHT, Holons are uniquely identified by their ActionHash. However, sometimes it is also useful to specify a property or properties whose value(s) uniquely identify holon instances. Defining such constraints allows the MAP Holons component to enforce those uniqueness constraints. They also offer optimized access paths for queries on collections of Holons. Each constraint specifies the (ordered) list of properties whose concatenated values comprise a unique key for this Holon type.
An access path is somewhat analogous to an index in a traditional database. It provides a means to optimize the performance of certain queries that require sorted, paginated, and/or filtered results.
Each offered access path is identified by a name and references a PropertyNameList. The PropertyNameList specifies a list of property_names defined for this HolonType that should be populated in the SmartLinks created for that access path. By including values for those properties in the SmartLink, the MAP Query Engine can filter and sort SmartLinks without having to retrieve the "Holon" for each link.