FLink is a tool that was developed to handle large quantities of input and output data. It enables you to traverse from a group of records in a source database to a ranked list of associated records in a destination database. For example, it can accept up to 100,000 protein sequence, gene, or small molecule identifiers as input and retrieve a ranked list of up to 100,000 biosystems. More information and illustrations are available in the FLink documentation:

• About FLink
• Illustrated quick start guide (example: proteins → biosystems)
• Textual step-by-step guide (example: proteins → biosystems)

Although FLink was initially developed as a companion tool for the BioSystems database, it can also be used in a similar way for other types of input and output data, as noted in the list of FLink's supported databases.

E-Utilities are tools that provide access to data within NCBI's Entrez system outside of the regular web query interface. They provide a method of automating Entrez tasks within software applications. Each utility performs a specialized retrieval task, and can be used simply by writing a specially formatted URL.