DART: A Framework for Distributed Audio Analysis and Music Information Retrieval - Intelligent Music Information Systems: Tools and Methodologies - page 230

Figure 5. Super-peer package submission protocol: Sample network topology and sequence of exchanged
messages to execute one package cycle

1. package advert
2. package query
3. package assignment
4. package download

5. results advert
6. results query
7. results

which are XML files describing the properties
of the algorithms to be executed (task graph
parameters containing the units/tools, platform
requirements if any, information about required
input audio data files, etc.), and sends them to
the local rendezvous super peer, which stores the
adverts. Each worker, when ready to offer a frac-
tion of its CPU time, either sends a new package
query that travels the network through the super-
peer interconnections or continues working on its
current workflow. A package query is expressed
by an XML document that requests if there are
any updates to the package it is currently using to
perform the analysis. The query can also contain
hardware and software features of the worker
node, if this is necessary—for example, available
RAM, disk space or JDK version. As soon as the
package query finds a matching package advert,
that is, an advert describing a package that can
be actually executed by the requesting worker,
a package assignment is made to the worker.

Package assignment is sent by the rendezvous
that stores the advert directly to the worker. The
actual packages are also stored locally on the
package repositories (whose adverts are cached
by the super peers), which query for new pack-
ages to download and store, and then re-advertise
the packages in order to propagate them onto the
network in a more decentralized fashion, rather
than relying on one node to do this, which is the
case for systems like SETI or BOINC. It may
be the case that a super peer is also a package
repository, if the peer chooses to donate these
resources, and has them to spare.
Since more than one package repository can
match the query, the package repository does not
directly send the package to the worker. Rather,
it returns a small package advertisement to
the worker, possibly via other super peers. The
worker itself initiates the download operation
after receiving the first package advertisement
that has matched its query and simply discards