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Endpoint
Name:FPDSAccessor
Description:
Id:FPDSAccessor
Category:accessor
Identifier Syntax

FPDSAccessor is an accessor using a standard identifier grammar:

<grammar>
  <group>fpds:/
    <regex type="anything" />
  group>
grammar>

with the following arguments: (for more details on argument passing details see here)

ArgumentRulesTypingDescription
No arguments defined
Request Verbs

The following verbs are supported:

Verbs
SOURCESINKEXISTSDELETE
Response

The response representation of this accessor for SOURCE requests is unknown.

This accessor throws no documented exceptions.

Import Requirements

To use FPDSAccessor accessor you must import the module urn:org:netkernel:mod:pds:

<import>
  <uri>urn:org:netkernel:mod:pdsuri>
import>

fpds:/ stands for Failover Persistant Data Service.

Requests for fpds:/ resources will first be attempted in the pds:/ scheme - if the resource is not found then the scheme will failover and attempt to source a default resource from the res:/ scheme.

Zones and Implementation

See the PDS Guide for details on these aspects of PDS.

Common Usage Pattern

Often configuration state will be non-existing on first use of an application. In general an application will try to use pre-existing state but when it is not yet present it is valuable to fallback to default preset state.

fpds:/ offers a graceful failover when a resource does not appear in pds:/ it tries res:/ (which is the default scheme for module resources).

Therefore by using fpds: a developer does not have to attempt EXISTS requests on pds:/ followed by conditional logic to attempt to go to res:/ for defaults.

In pseudo code the fpds: scheme looks like

try
{ REQUEST pds:/XXXXXX
}
catch
{  REQUEST res:/XXXXXX
}

Immutability of res:/

Be aware that SINK, DELETE on fpds: will be performed on the pds: space since res:/ is an immutable address space.