c-tree provides ISAM functions, a set of high-level functions for manipulating data and index files. Each function performs multiple file and index access operations.
ISAM functions assume a hierarchical relationship among the data and index files, in the sense that each data file may have many indexes, while each index relates to only one data file.
For example, an accounts payable system may define a vendor data file indexed by vendor name and number, and an invoice data file indexed by vendor number and invoice number. In this case, each data file has two indexes. Although each data file is indexed by vendor number, there is a separate vendor number index for each data file.
ISAM functions assume the key values for each index are derived from the contents of the data records of the associated data file. As described later, the Key Segment parameter specifies how to extract a key value from a data record.