RFC 2968 (rfc2968) - Page 2 of 9
Mesh of Multiple DAG servers - Results from TISDAG
Alternative Format: Original Text Document
RFC 2968 Mesh of Multiple DAG servers October 2000
untouched, or a referral index server's contents could be aggregated
into a new index object, generating referrals back to that server.
The proposal is that the mesh should be constructed using index
objects aggregated over participating services' servers. That is,
referrals will be generated to other recognized services, not their
individual participants. This can be done as a hierarchy or a level
mesh one-layer deep, but the important reason for not simply passing
forward index objects (unaggregated) is that individual services may
support different ranges of access protocols, have particular
security requirements, etc. Referrals should be directed to a CAP or
CAPs -- either the standard ones used by the DAG system, or new ones
established to support particular semantics of remote systems (e.g.,
other query types, etc). Within a given DAG system, referrals to
these remote servers will look just like any other referral, although
a particular SAP or SAPs may be established to provide query
fulfillment (again, to enable translations between variations of
service, to allow secure access if the relationship between the
services is restricted, etc).
In the following scenarios of mesh traversal, the assumption is that
the primary service in discussion (Country A in Scenario 1, Country B
in Scenario 2) is a DAG-based service. The scenarios are presented
in the light of interoperating DAG services, but in most cases it
would be equally applicable if the remote service was provided by
some other service architecture. Again, the key element for
establishing a mesh of any sort is the exchange of the CIP index
object, not internal system architecture.
1.1.1 Scenario 1: Top Down
Suppose 2 countries tie their services together. A user makes a
query in Country A. A certain number of hits are made against the
index objects of A's WDSPs. There is also a hit in the aggregate
index of Country B. There are 3 possible cases under which this must
be handled:
Case 1:
Country A and Country B are running services that are essentially the
same -- in terms of protocols, queries, and schema that are
supported. In this case, one referral should be generated per
protocol supported by Country B's service. The referral can be
passed back as far as the client, if its protocol supports referrals.
Alternatively, the CAP may chain the referral through an appropriate
SAP, in the usual fashion. In other words, the CAPs of Country B's
service act as WDSPs to Country A's service.
Daigle & Eklof Informational