Sharing and Distribution of Wrappers

During the development of XWRAP, we encountered a number of interesting challenges. One category of issues is related to the design of Wrapper API. An interesting challenge is the identification of desirable and undesirable wrapper functionality as well as the mandatory and optional wrapper functionality. Another category of issues is related to the ways of creating a repository where wrapper programs can be shared and distributed among application developers.

In this paper we present a metadata approach to building an extensible wrapper repository system - WPstore. The goal of WPstore is to develop mechanisms and meta interfaces for sharing wrappers. The WPstore wrapper repository construction consists of two phases.

• The first phase includes the development of an extensible wrapper framework and a component library, called component library. This library hosts a collection of code components useful for constructing wrapper programs, and a collection of wrapper API functions, plug-ins, and meta-interfaces for applications to hook up with specific wrapper programs downloaded from the WPstore. The main issues in the first phase include the identification of mandatory functionality (such as sophisticated retrieval mechanisms, error handling, streaming mode and blocking mode), optional functionality (such as performance statistics, proxies, optimization), as well as undesirable functionality (such as massaging data, sophisticated recovery strategies).
• The second phase involves setting up a distributed metadata repository, to which wrapper-developers can contribute wrappers and the wrapper-users can download them. For example, we will provide a WrapperRepository object that provides install(...) and download(...) methods to implement this functionality. Issues in the second phase also include mechanisms for handling broken wrappers, metadata structure design for encoding information about wrappers, and issues on how to apply version control, etc.