The Simple Digital Library Interoperability Protocol

The Simple Digital Library Interoperability Protocol (SDLIP; pronounced S-D-Lip) is a protocol for integrating multiple, heterogeneous information sources. It was developed jointly by Stanford University, UC Berkeley, UC Santa Barbara, the San Diego Supercomputer Center, and the California Digital Library Project. Clients use SDLIP to request searches to be performed over information sources. The result documents are returned synchronously, or they are streamed from service to client as they become available. Implementations can be constructed over HTTP or CORBA based transports. In fact, any search service can be accessible through both kinds of transports at the same time. Implementations for IETF's HTTP-based DASL protocol, and for CORBA are available.

Detailed information about SDLIP is available, as well as a streaming video.

Figure 1 below shows a typical example of where SDLIP is relevant.

Figure 1: The Role of SDLIP in a Digital Library Architecture With Autonomous Sources and Wrappers

The dotted line in Figure 1 indicates a network boundary: entities on the same side of the line are assumed to be in the same address space. Note in Figure 1 that the information to be served is stored in repositories that do not (necessarily) implement SDLIP.

SDLIP wrapper in Figure 1 wraps two external sources. Through its back end, the wrapper interacts with the external services via the transport and higher-level protocols required for these services. At the front end, the wrapper supports SDLIP. Of course, an information source may itself provide SDLIP access. In that case, the client can interact directly with the source.

The basic interaction is for the client to request a search across the network. Part of the request specifies how many documents are to be returned initially, once the search will be complete. The request also specifies which portion of each document is to be returned. For example, the client might ask for authors and titles of the first 10 documents to be returned right away. The client may later request more documents of the result, or it may request additional portions of the documents already delivered.

Figure 2 shows the interfaces that define SDLIP.

SDLIP Interfaces

Figure 2: SDLIP Interfaces

The Search Interface defines operations necessary to initiate searches. The Metadata Interface allows clients to explore an information source's capabilities. The Delivery and Result Access interfaces are optional facilities for asynchronous information access.