Pattern-Based Schema Mapping and Query Answering in Peer-to-Peer XML Data Integration System - Advanced Database Query Systems - page 241

Figure 8. Queries and propagations tables in 6P2P. Sample data illustrates instances of tables when a
query is propagated from a peer @P to a peer @P'

a cycle, i.e. @ P' occurs in q 1. qryTrace . discoveryMayBeDone ( q 1, @ P ) is true if the hypothesis of
Theorem 1 does not hold. acceptedPropagation ( q 1, @ P' )$ is true if @ P' accepts the propagation of q 1
with the given parameters.

Algorithm 3 . ( query propagation )

Input : @ P - a current peer; @ P : Peer , @ P : Partners , @ P : Queries , @ P : Propagations
- tables in the peer's @ P database.
Output : New states of tables @ P : Queries and @ P : Propagations , if a partner peer
@ P' accepts the propagation.
Method:
q := @ P : Queries ; // a row describing the query thread to be propagated if q.
propagMode = ' P2P ' {
q 1 := new propagationParametersType ;

// used to prepare propagations to all partners

q 1. propagId := new propagId ;

q 1. qryThreadId := q.qryThreadId ;

q 1. qryId := q.qryId ;

q 1. qryTrace := q.qryTrace + @ P ;

// the sequence of visited peers used to avoid cycles

q 1. myPeer := @ P ; // the peer where the answer should be returned