![](bg5.png)
services (from the framework core or otherwise)
may be replicated as long as they meet some
requirements – for the libraries/executables to be
portable and the destination peer to have the
necessary operating system and platforms. These
requirements are stored in peers as XML documents.
Core services already make use of open-source
portable libraries, and can therefore be replicated on
request. Also, the SOA/P2P decoupling allows for
the same functionality to be provided by different
libraries in various programming languages, as long
as they have the same signature and URI. With
every instance of a digital library, a common XML
configuration file resides in every peer, where
automatic replication may be set on or off. When set
to on, peer services whose clients are being queued
can broadcast a replication request to other nodes
and copy the necessary libraries to the first peer to
reply.
5.1.4 Other Services
Interoperability is a key factor in digital libraries,
and OAI-PHM protocol is being widely adopted to
promote a simple consumption (harvest) of metadata
from institutional repositories. The SOPPA
framework makes available a simple OAI provider
service, which dynamically queries a peer group and
delivers OAI-PHM responses with the data
resources available. While it is more efficient to
have this provider at the super-peer, it can be placed
(and replicated) in edge peers.
To simplify the development of more complex
services, one can also build composite services,
which make use of existing, simpler ones. While this
can be achieved with a simple sequence of proxy
calls in the code, it is sometimes convenient to
provide a declarative, XML based, composite
service description. It is being considered the
support for business process languages such as
BPEL in the future.
6 CONCLUSIONS
Unlike existing digital library solutions, the
proposed framework takes advantage of the benefits
from both P2P networks and SOA architectures, by
adopting an architecture which integrates the two
paradigms. Although some features are still under
development, it can already simplify the job of
creating a new digital library from scratch.
As a future work, we expect to perform stress
tests and performance measurements, and compare it
to the existing digital library and archive from our
institution, which holds thousands of heterogeneous
documents and already takes advantage of some
services distributed in other information systems.
Future versions of the framework should include
more services and solve issues such as declarative
style business process execution. Also, support for
REST-style web services should be added.
ACKNOWLEDGEMENTS
This work was funded in part by FCT – Portuguese
Foundation for Science and Technology – grant
number SFRH/BD/23976/2005.
REFERENCES
Agosti, M. et al., 2006. D1.1.1: Evaluation and
comparison of the service architecture, P2P, and Grid
approaches for DLs. Technical Report, DELOS – A
Network of Excellence on Digital Libraries.
Bainbridge, D. et al., 2001. Greenstone: A platform for
distributed digital library applications. In
Constantopoulos, P., & Solvberg, I.T. (Ed.), Research
and Advanced Technology for Digital Libraries (pp.
137-148). Springer.
EPrints, 2007. EPrints for Digital Repositories. http://
www.eprints.org
Gong, L., 2001. JXTA: a network programming
environment. Internet Computing, 88-95. IEEE.
Lagoze, C. et al., 2005. Fedora: an architecture for
complex objects and their relationships. In Inter-
national Journal on Digital Libraries, 6 (4), 124-138.
Ma, Y., Aygun, R.S., 2005. Peer-to-peer based multimedia
digital library. In Proceedings of the Thirty-Seventh
Southeastern Symposium on System Theory, SSST
'05, 130- 134.
Mastroianni, C., Talia, D., Verta, O., 2005. A super-peer
model for resource discovery services in large-scale
Grids. Future Generation Computer Systems, 1235-1248.
Mazurek, C., Werla, M., 2005. Distributed services
architecture in dLibra Digital Library Framework.
Future digital library management systems: System
architecture and information access, 26-31. DELOS.
Mischke, J., Stiller, B., 2004. A methodology for the
design of distributed search in P2P middleware. IEEE
Network, 30-37.
Nedjl, W. et al., 2002. EDUTELLA: a P2P networking
infrastructure based on RDF. In Proceedings of the
11
th
international conference on World Wide Web,
604-615.
Ratnasamy, S. et al., 2001. A scalable content-addressable
network. ACM ISGCOMM, 161-172.
Ripeanu, M. (2001). Peer-to-Peer architecture case study:
Gnutella network. In Proceedings of the First
SOPPA - SERVICE ORIENTED P2P FRAMEWORK FOR DIGITAL LIBRARIES
219