LORE: A Lightweight Object REpository for Semistructured Data

Abstract

LORE: A Lightweight Object REpository for Semistructured Data Dallan Quass, Jennifer Widom, Roy Goldman, Kevin Haas, Qingshan Luo, Jason McHugh, Svetlozar Nestorov, Anand Rajaraman, Hugo Rivero, Serge Abiteboul, Jeff Ullman, Janet Wiener Stanford University Database Group, http://db.stanford.edu The number of information sources accessible electronically is growing rapidly. Many of these sources store and export unstructured data in addition to or instead of structured data. In most cases, however, the unstructured data is not entirely devoid of structure, i.e., the data is semistructured. We consider data to be semistructured when there is no schema fixed or known in advance and when the data may be incomplete or irregular. For example, HTML files on the World-Wide Web usually contain some structure, but often the data is irregular or In addition, data integrated from multiple, heterogeneous information sources often is semistructured. Storing and querying semistructured data poses considerably different problems and requirements than those for traditional databases, where data storage and query processing are dependent upon structured data. Relational, nested-relational, and object-oriented database systems, for example, all depend upon the data having a known and regular schema. We have developed a system called LORE (for Lightweight Object REpositoryand a query language called LOREL (for LORE aimed specifically at handling semistructured data. The data model used in Lore is a "lightweight" object model called OEM (for Object Exchange Model) [3]. OEM is a simple, self-describing model with object nesting and identity. Because we use Lore primarily for storing and querying data obtained from other information sources, Lore itself also is "lightweight," in the sense that it is a repository and a query engine but not a full-feature database management system. Currently, Lore does not provide transaction management, concurrency control, or recovery. Lorel, the query