Chapter 3


3.1 Overview

The framework of the UNITE project consists of an enhanced WWW server, server tools, and a Macintosh client. These applications provide a mechanism for users to access multimedia resources in a database. The contents of the database are contributed by the user community. In our driving application, a two-stage review process is used to review these contributions (Figure
Figure 3-1: UNITE: An Information Service for Contributing, Coordinating and Distributing Educational Resource

3.2 The Database

The database is primarily used to organize the resources. Each database has a configuration file associated with it which describes the structure, format, and treatment of the database records. Databases can store several classes of information and must be capable of managing significantly different kinds of data (i.e. software, text, video, audio, etc...). A database configuration language provides a centralized user-readable and modifiable specification of the data stored and its treatment by the system. Following the definition of a database, the records need to be entered and ultimately presented to the user. The records are indexed using the CSO database and are then rendered in HTML. The HTML generation is currently done at contribution time but could be done on-the-fly if it were desirable to trade time for space.

3.3 The UNITE Server

The UNITE server is based on HTTP which has been used by the Web community since 1990 and therefore allows it to be used as a regular Web server. It supports the standard request methods with the addition of the SEARCH method. It runs CGI scripts and supports user directory access. On the other hand, the UNITE server does not support directory indexing, authentication, and a number of other services which were not required for our driving application. The SEARCH method is a unique feature of the UNITE server. It was created to allow the server to directly respond to queries from the client rather than via CGI scripts. It also defines a search syntax, which has yet to be done by the Web community. To support access from other WWW clients, which do not support the SEARCH method, a generic forms interface to the search capability was built. This interface allows the user to select which database and which fields of the database to search on. The current search engine used for UNITE is CSO. CSO was originally written for a simple name service, a computer resident phone book, but required only slight modifications to fit UNITE's needs. It can keep relatively small amounts of information about a relatively large number of objects, and provide fast access to that information over the Internet
[4]. CSO also allows for wild card expansion which permits users to be conveniently vague when formulating queries. Another search engine that is currently being integrated into the UNITE server is WAIS. WAIS (Wide Area Information Server) is a free text search engine which would support natural language queries and allow the user to perform inexact searches. Another advantage of WAIS is that it returns a ranked list of matches. This allows the user to select resources that have the best match to the query instead of having to browse through a set of resources to find the best.

3.4 Client: User Interface

The client was based on a prototype developed during earlier pilot projects [1]. This design used a layered approach to represent hierarchal structures similar to the approach used to represent directories in typical graphical user interfaces. Novice users understand how to navigate this structure and they are successful in locating useful resources. The pilot users also provided several suggestions for improving the client interface. Key among these were suggestions for more efficient browsing views of those hierarchical structures and the ability to locate items using multiple selection criteria.

Figure 3-2: The Explorer Client Search Window
The recent user interface development has been centered on incorporating recent additions to HTML for presenting an easy-to-use interface for constructing Boolean queries using standard WWW clients. Figure 3-2 shows a user constructing part of a Boolean query by specifying, in this case, curriculum values. Additional controlled vocabulary fields may be coupled with remaining text entry fields to form complex queries for specifying resources.

3.5 Distributed Aspects

The success of UNITE as a model for distributed access to collections of information across the Internet depends on a number of factors, but the single most important is ensuring that the system provides good support for adding to the database. Our driving application is a particularly good example of this since the educational materials are contributed by the users of the system, rather than by some central authority. However, we believe that this is one of the strengths of the Internet and represents an important aspect of systems which look toward the future of the National Information Infrastructure.

First and foremost, the success of such a database requires the participation of users, who are often the best qualified people to generate source material as practitioners in the field. With this in mind, we implemented a method we called the Contribution Process, supported by software called the Contributor. The Contributor must first know to which database the user wishes to contribute a record. Then the Contributor prompts the user to enter information for each field of the database. The Contributor then sends the newly defined record to a local reviewer. The local reviewer's duties are to make sure the record relates to the application area to which it is being contributed, that it is properly formatted, and is well written. The local reviewer then passes the record along to a master reviewer whose duties are to check the local reviewer's work and approve or reject the record for inclusion in the database. From there, the record is sent to the UNITE server for integration in the database. Currently this is done using FTP but in the future the PUT method will be used. The idea here is that the record is sent to a centralized server, keeping the databases consistent by ensuring that there is only one place where new information is introduced to the system. Once the record is transferred to the server, a series of steps is taken to add the record to the proper database. The first step is to generate an HTML document following the format of the database record definition. Note that this is done on the server and not by the user, keeping a consistent look and feel for all the HTML representations of the database records. Once the database record has been created, it is then added to the database. The final step is to generate a new layered and outline view and to rebuild the database indices. This will allow users to request or search for the newly contributed record.

This Contribution Process is currently run nightly and therefore the time for a newly defined record to appear in the database is usually 24 hours. To distribute server load and improve availability, UNITE supports a method of creating multiple copies of a database on multiple server machines, which is called mirroring. The mirroring process is currently run every night and operates in two modes. The first mode makes a complete copy of the database file structure, including all HTML documents and all indices built by CSO, to the mirrored server. This method is usually used for newly added servers or those that have been inactive for a long period of time. The second method is used for updates to active mirrors. It determines the set of files modified since the last update of the mirrored server and sends. None of the mirrored servers are allowed to receive contributions, thus helping to ensure database consistency.