2.5.1.1 Internet
2.5.1.1.1 Physical structure
2.5.1.1.2 Virtual structure
2.5.1.2 Knowledge representation and organization
2.5.1.2.1. Databases
2.5.1.2.2 Extended markup language (XML)
2.5.1.2.3 Ontologies
2.5.1.3 Agents
2.5.1.3.1 Mobile agents
2.5.1.4 Human-computer interaction
2.5.1.4.1 Program interfaces