1. Introduction
2. Keyword Based Querying
   1. Single-Word Queries
   2. Context Queries
   3. Boolean Queries
   4. Natural Language
3. Pattern Matching
4. Structural Queries
   1. Fixed Structure
   2. Hypertext
   3. Hierarchical Structures
      1. A Sample of Hierarchical Models
      2. Discussion
   4. Query Protocols
   5. Trends and Research Issues
   6. Bibliographic Discussion

With G. Navarro