## 6 Implementation and Application of the PORTAL-DOORS System
### Infrastructure System versus Tools and Applications versus Content  
PORTAL-DOORS as a lower-level infrastructure system must be distinguished from higher-level tools and applications built on the foundation of the infrastructure. PORTAL-DOORS as a mobile metadata management, communication, and distribution system must also be distinguished from the actual metadata that the infrastructure is designed to send, receive, and exchange throughout the system. Fundamentally, the PORTAL-DOORS System establishes an interoperable, platform-independent, application-independent, messaging interface standard for information exchange over the internet. The design of this infrastructure system is guided by the HDMM architectural style and mandated to fulfill additional requirements in order to serve both the original web and semantic web as specified in the blueprint paper [1], here in this report, and partially implemented in the current draft version 0.6 of a reference implementation written in XML Schema *.xsd files. Work to complete this reference implementation must clarify and stabilize not only the structural data model for the resource records and messages, but also the functional behavioral model for the PORTAL and DOORS services in response to requests from clients. Servers and clients must also communicate over transport protocols. The PORTAL-DOORS Project maintains a vision of serving more than one transport protocol as discussed in Section VII.E. of [1]. Initial drafts of the PDS schema files (prior to version 0.5) assumed use of the IRIS core protocol. The previous draft (version 0.5) addressed only the structural data model. The current draft (version 0.6) has re-introduced use of a specific transport protocol but replaced the IRIS core protocol with an http protocol using RESTful web services. At present, in a bootstrapping stage of development for the PORTAL-DOORS System, RESTful web services provide a more favorable environment for promoting adoption of the system. However, a fully dedicated and optimized protocol specifically for PORTAL-DOORS may ultimately prove necessary to achieve the speed and efficiency comparable to that which exists now for IRIS-DNS. As PORTAL-DOORS continues to be developed and implemented, any client tool, application, or web site that accesses PORTAL-DOORS must be distinguished from the system itself. The PORTAL-DOORS System should not be considered either a single site or repository any more than the IRIS-DNS System of domain name registries and directories could be construed to be a single site or repository. For both IRIS-DNS and PORTAL-DOORS infrastructure systems, server-side data stores and services and client-side tools and applications can be written in any language on any platform. Client tools are necessary for agents to edit the information maintained at an individual server data store. Client tools are also necessary for agents and users to navigate, search and query the information stored not only at a particular server but also throughout the entire network of servers. These tools include faceted browsers, keyword search utilities, and SPARQL query interfaces. Even more complex applications can be built in which the navigation, search, and query tools may be embedded within more sophisticated applications that hide these tools from the user interface. An important example is an application component that would provide natural language answers to natural language questions in the context of the overall function of the software application. In this example,the component converts the user's natural language question to a SPARQL query submitted to PORTAL-DOORS, and then converts the query response from PORTAL-DOORS back to a natural language answer for presentation to the user. The usefulness of any technology system designed to manage content, regardless of how it is constructed from interface standards, server networks, client tools, and applications, is only as good as the content that it manages and exposes to producers and consumers of the content.