XML and Metadata in P2P Systems: Applications


Now that we have reviewed the basics of XML and metadata, the application areas that are beneficial for P2P frameworks may seem evident. Core areas for leveraging XML and metadata in P2P systems include messaging, content management, data storage, and software distribution.

Messaging

Although messaging is nothing more than communication between peers, XML offers a platform-neutral format for sending short structured messages between peers for communication or exchanging content. The use of XML messages allows for many different kinds of peers to discover, participate, and communicate with each other. Many P2P frameworks like Napster and Gnutella have their own protocols for communication. If these two frameworks need to exchange data, using XML in the underlying protocol for each will solve this integration issue quite easily, provided there is a "translation," using XSLT or something like it. Thus, different applications that work on different platforms and talk different message dialects can interact and exchange information by using this stylesheet to convert between disparate formats. The mapping requirements in order to build these stylesheets require an understanding of both protocols' message formats and vocabularies, but once achieved, they provide a powerful message exchange medium. XML can also be leveraged at the messaging layer to broadcast metadata to a peer group. This example is embodied in JXTA by advertisements that can be represented in XML.

Content Management

Enterprises often manage data within their environments via either a centralized portal or replicated servers. Web portals are centralized hubs that present data for companies and their respective suppliers or partners in a single user interface; in order to share data, participants must somehow get it onto the portal. This cumbersome approach not only requires significant maintenance, but is also disruptive to work processes that require data to remain in its original locations. Replicated servers is a system wherein each corporation or department uses its own server for storing information; periodically, each server must synchronize with or replicate its data to each of the other servers. This has a disadvantage for the user who wants to see recent data; he might not be looking at the most up-to-date information because of the synchronization schedules or because of network partitioning or other connectivity issues.

By moving to a P2P framework, decentralized access to content in its native format becomes a reality. As the content can remain on the respective servers, more granular control of the information can be applied. To construct such a framework, a robust technology foundation and an effective search engine construct is required in order to discover the information, and then subsequently orchestrate how the information is accessed. The initial stage of discovery is a key area for the role of metadata in P2P frameworks.

XML As Data Sources

In most IT environments, data is stored in one of two ways. The first method uses custom or unstructured data formats. A second approach uses a relational database to store the information and manage the relationships between the data records. Because true P2P systems have no central server for managing information between peers, efficiently distributing and storing application data for peer access is not a trivial task. Data often has to reside locally on the peer for processing; XML provides for a simple and lightweight interchange format suitable for network transmission.

XML As P2P Application Deployment Model

As the number of peers in a P2P network expands, the issues with application deployment dramatically increase. One XML-based solution to this problem is the Open Software Description Model (OSD). OSD files enable system architects to define the application components required for peer applications, along with the locations to download these components and any component dependencies. Each peer can verify that it has the most recent software components and automatically download upgrades if needed. The goal of the OSD format is to provide an XML-based vocabulary for describing software packages and their interdependencies, whether it is peer initiated (pulled), or automated (pushed). Using an XML data model, the markup tags in the OSD vocabulary are represented as elements of a tree. Effectively integrating OSD files into a P2P deployment strategy shifts the burden of software upgrades from the user to the P2P application itself.



JavaT P2P Unleashed
JavaT P2P Unleashed
ISBN: N/A
EAN: N/A
Year: 2002
Pages: 209

flylib.com © 2008-2017.
If you may any questions please contact us: flylib@qtcs.net