(PLS, WAIS)
Authentication features help support subscription-based online services. Some engines are also equipped with billing options that allow for customized prices to be set either per database, per document, or per number of characters downloaded (see the following figure). The activity log may keep track of:
- Total Number Of Connections
- Number of Different Machines Connecting
- Total Number of Searches
- Total Connect Time
- Total Search Time
- Searches Returning Zero Hits
- Total Number of Documents Retrieved
- Total Number of Databases Searched
- Number of Searches with no Database Name
- Number of Searches Requesting Help
- Average Number of Seed Words per Search
- Number of Searches using Relevance Feedback
- Number of Server Warnings
- Number of Server Errors
- Number of Search and Retrieval Requests for each database
- List of Client Machines
- Client Information
See also ``client / server'' and ``security''.