content/apacheds/advanced-ug/4.2.4.2-prescriptiveaci.mdtext

Title: 4.2.4.2 - PrescriptiveACI
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# 4.2.4.2 - PrescriptiveACI

Prescriptive ACI are access controls that are applied to a collection of
entries, not just to a single entry. Collections of entries are defined by
the subtreeSpecifications of subentries. Hence prescriptive ACI are added
to subentries as attributes and are applied by ApacheDS to the entries
selected by the subentry's subtreeSpecification. ApacheDS uses the
**prescriptiveACI** multivalued operational attribute within subentries to
contain ACIItems that apply to the entry collection.

Prescriptive ACI can save much effort when trying to control access to a
collection of resources. Prescriptive ACI can even be specified to apply
access controls to entries that do not yet exist within the DIT. They are a
very powerful mechanism and for this reason they are the preferred
mechanism for managing access to protected resources. ApacheDS is optimized
specifically for managing access to collections of entries rather than
point entries themselves.

Users should try to avoid entry ACIs whenever possible, and use
prescriptive ACIs instead. Entry ACIs are more for managing exceptional
cases and should not be used excessively.

<DIV class="info" markdown="1">
**How it works!**
For every type of LDAP operation, ApacheDS checks to see if any access
control subentries include the protected entry in their collection. The set
of subentries which include the protected entry are discovered very rapidly
by the subentry subsystem. The subentry subsystem caches
subtreeSpecifications for all subentries within the server so inclusion
checks are fast. 

For each access control subentry in the set, ApacheDS checks within a
prescriptive ACI cache for ACI tuples. ApacheDS also caches prescriptive
ACI information in a special form called ACI tuples. This is done so
ACIItem parsing and conversion to an optimal representations for evaluation
is not required at access time. This way access based on prescriptive ACIs
is determined very rapidly.
</DIV>