Change detection in structured documents (e.g. SGML) is important in many applications including data warehousing, digital libraries and Internet databases. The paper presents a graphical environment for detecting changes in the structured documents. The authors represent each document by an ordered labeled tree based on the underlying markup language. They then compare two documents by using previously developed algorithms for pattern matching and pattern discovery in trees. Several operators are developed to support the comparison of the documents; graphical devices are provided to facilitate the use of the operators. They believe the proposed tool is useful for not only document management, but also software maintenance, particularly configuration management and version control, where programs are represented as parse trees and detecting changes in the trees provides a way to find the syntactic differences of two program versions.

Structural matching and discovery in documents such as SGML and HTML is important for data warehousing [6], version management [7, 11], hypertext authoring, digital libraries [4] and Internet databases. As an example, a user of the World Wide Web may be interested in knowing changes in an HTML document [2, 5, 10]. Such changes can be detected by comparing the old and new version of the document (referred to as structural matching of documents). As another example, in hypertext authoring, a user may wish to find the common portions in the history list of a document or in a database of documents (referred to as structural discovery of documents). In SIGMOD 95 demo sessions, we exhibited a software package, called TreeDiff [13], for comparing two latex documents and showing their differences. Given two documents, the tool represents the documents as ordered labeled trees and finds an optimal sequence of edit operations to transform one document (tree) to the other. An edit operation could be an insert, delete, or change of a node in the trees. The tool is so named because documents are represented and compared using approximate tree matching techniques [9, 12, 14].