A Logical Foundation for Nested Semi-structured Data and Web Forms

Semi-structured data are commonly represented by labeled flat db-graphs. In this paper, we study an extension of db-graph model for representing nested semi-structured data. This extension allows one to have db-graphs whose vertex labels are db-graphs themselves. Bringing the data model closer to the natural presentation of data stored via Web documents is the main motivation behind nesting db-graphs. The importance of nested db-graphs is similar to the importance of nested tables in relational model. The main purpose of the paper is to provide a mechanism to query nested semi-structured data and Web forms in a uniform way. Most of the languages proposed so far have been designed as extensions of SQL with, among others, the advantage to provide a user-friendly syntax and commercial flavor. The major focus of the paper is on defining a graph query language in a multi-sorted calculus like style.