Dynamically Generating Conceptual Browsing Interfaces for Digital Libraries Using SVG

Overview

In this paper we present a system that supports the dynamic generation of conceptual browsing interfaces for digital libraries using SVG. This system is part of the Strand Map Service (SMS), a service being developed for the National Science Digital Library (NSDL). The SMS aims to provide educators and learners with conceptual browsing interfaces that help them to locate and use learning resources in educational digital libraries. These interfaces are comprised of interacting visual components that contain different views onto a concept space that can be modeled as nodes and links (Strand Maps). Rather than creating a static presentation of these interfaces, the system generates visualizations of these interfaces dynamically using SVG techniques from information modeled in the data repository. Our approach builds on recent advances in visualization components and programmatic interfaces to knowledge organization systems.

Concept Browsing Interfaces

Concept browsing interfaces, based on nationally recognized education standards, can help educators and learners to locate, comprehend and use educational resources in digital libraries. These interfaces provide navigational and orientational cues that are typically lacking from traditional keyword or fielded search interfaces.

Service Impact

• Digital Libraries' Perspective: By dynamically generating conceptual browsing interfaces in SVG, the Strand Map Service will enable digital libraries to organize their resources around science content standards. This novel application of webmapping demonstrates the real-time generation of progression-of-understanding maps through SVG-database connectivity.
• End User's Perspective: By generating interactive SVG components based on web services (described below), the conceptual browsing interface provides users a gateway for information discovery in distributed digital libraries. As described below, we provide a query language which can be used by different digital libraries to request the generation of an SVG visual interface linked to their individual on-line resources.

System Features

• Client-Server Architecture:

  The server is based on the struts architecture. It consists of a client request handler to analyze user requests and generate a service call; an application logic to dynamically generate visual interfaces in SVG; and a data resources component to connect to Relational Database (Microsoft SQL Server 2000) at backend and generate and execute SQL Query.

  The client consists of the Interface Window and the Viewer.

• Services as Communication Media:

  We developed a web services-based protocol—the Concept Space Interchange Protocol (CSIP)—to enable communications between client and server. The protocol design is based on REpresentational State Transfer (REST) web architecture style. CSIP is implemented in XML. The protocol defines a query language which is used by the client to initiate the request to generate SVG components. When the CSIP query is sent to the server, it dynamically generates SVG as the front end of this web services and sends back the SVG as a query result to the client through CSIP.

• Server-Side Dynamic Generation of the Visual Interface in SVG:

  In order to present the visual interfaces in response to user's request, instead of storing static visual interfaces the server generates SVG dynamically by retrieving data from a backend database. A visualization algorithm that we have developed is then applied to dynamically generate a graphical representation of the concept browsing interface in SVG.

Visualization Algorithm

The conceptual browsing interfaces contain visual components which are modeled as nodes and links. It is a form of directed acyclic graph. The visualization algorithm we developed uses tree-based processing where a strand map is viewed as consisting of a special tree with multiple roots. Breadth first search is used to compute the vertical depth level of each node relative to its nearest root. Depth first search is used to compute the horizontal relationships, across strands and within a strand, between nodes at the same vertical depth. The results of these two searches are combined to quantitatively identify internal relations between nodes. These quantitative relations are then used to allocate nodes to placements within a predefined grid that represents the available drawing space. When pairs of nodes conflict, local placement adjustments are then made by moving the conflicting node to the next available placement in the grid.

System Architecture

Figure 1 - System Architecture

User Request Analyzer Component:

• Receives queries from the client through CSIP
• Analyzes and translates these requests to a graphical query (XML)
• Sends graphical query to the Data Resource Component

Data Resource Component:

• Parses the graphical query and generates corresponding SQL query using XSLT
• Executes SQL Query
• Gets the result set from the database
• Creates the data structure used by the Graph Layout Component

Graph Layout Component:

• Implements the visualization algorithm in Java
• Uses the Rules and Aesthetics Component to create the requested conceptual browsing interface
• Encodes the result in SVG format

Rules and Aesthetics Component:

• Defines graph drawing rules
• Represents the semantic constraints and the aesthetic heuristics
• Defines the priorities guiding rule application

The Strand Map Service demonstrates the utility of dynamically generated SVGs as conceptual browsing interfaces for digital libraries.