data structures using is pointer that points to the position at which next read/write operation will be performed indicates whether the file is text file or binary file index table stores and of the record in the file in sequentially ordered file the index whose search key specifies the sequential order of the file is defined as the index files are frequently used indexing technique in document retrieval systems for large textual databases is collection of data organized in fashion that facilitates updatingretrievingand managing the data