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Indexed Sequential Access Method (ISAM) is a method for creating, maintaining, and manipulating computer files of data so that records can be retrieved sequentially or randomly by one or more keys. Indexes of key fields are maintained to achieve fast retrieval of required file records in indexed files .
An indexed file is a computer file with an index that allows easy random access to any record given its file key. The key must be such that it uniquely identifies a record. If more than one index is present the other ones are called alternate indexes. The indexes are created with the file and maintained by the system.
Index is a full index so data file does not have to be ordered; Pros and cons versatile data structure – sequential as well as random access; access is fast; supports exact, range, part key and pattern matches efficiently. volatile files are handled efficiently because index is dynamic – expands and contracts as table grows and shrinks
Pervasive initially used the term "navigational database" to describe Btrieve, but later changed this to "transactional database". The use of the term navigational database was unusual because a navigational database uses "pointers" and "paths" to navigate among data records, and these pointers are contained in the record itself; ISAM, which is the fundamental structure of Btrieve, uses a ...
A database-utility program would use the database description file to create the remaining components of the database. Proprietary language compilers (such as COBOL and ALGOL) would use the database description file to create database-related elements in the object code of the compiled program. These compilers used language extensions to ...
Sequential access is a term describing a group of elements (such as data in a memory array or a disk file or on magnetic-tape data storage) being accessed in a predetermined, ordered sequence. It is the opposite of random access , the ability to access an arbitrary element of a sequence as easily and efficiently as any other at any time.
The KSDS organization was designed to replace ISAM, the Indexed Sequential Access Method. Changes in disk technology had meant that searching for data in ISAM data sets had become very inefficient. Changes in disk technology had meant that searching for data in ISAM data sets had become very inefficient.
A database index is a data structure that improves the speed of data retrieval operations on a database table at the cost of additional writes and storage space to maintain the index data structure. Indexes are used to quickly locate data without having to search every row in a database table every time said table is accessed.