Why is information retrieval so difficult?

The reasons for the difficulties are:

1. Research is usually conducted across multiple sites on the web and in different jurisdictions(often world-wide).

2. Wide use of differing relevance ranking systems.

3. The differing role of web spiders to build searchable collections of remote documents.

4. The complex relationship between directories and search engines.

5. Differences between the functionality of electronically based research services and the goals of effective legal research

Source: http://laws1032.russell-allen.com/materials/

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