An entry-sequenced data set (ESDS) is a type of
data set A data set (or dataset) is a collection of data. In the case of tabular data, a data set corresponds to one or more database tables, where every column of a table represents a particular variable, and each row corresponds to a given record of the d ...
used by
IBM's
VSAM Virtual Storage Access Method (VSAM) is an IBM DASD file storage access method, first used in the OS/VS1, OS/VS2 Release 1 (SVS) and Release 2 (MVS) operating systems, later used throughout the Multiple Virtual Storage (MVS) architecture and no ...
computer data storage system.
Records are accessed based on their sequential order, that is, the order in which they were written to the file; which means that accessing a particular record involves searching all the records
sequentially
In mathematics, a sequence is an enumerated collection of objects in which repetitions are allowed and order matters. Like a set, it contains members (also called ''elements'', or ''terms''). The number of elements (possibly infinite) is called ...
until it is located, or by using a relative physical address (''Relative byte address'', RBA), i.e. the number of bytes from the beginning of the file to start reading.
Keys may be used to access records in an ESDS by defining an alternate index.
See also
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Key Sequenced Data Set
A key-sequenced data set (KSDS) is a type of data set used by IBM's VSAM computer data storage system. Each record in a KSDS data file is embedded with a unique key. A KSDS consists of two parts, the data component and a separate index file kn ...
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Linear Data Set
A linear data set (LDS) is a type of data set organization used by IBM's VSAM computer data storage system.
The LDS has a control interval size of 4096 bytes to 32768 bytes in increments of 4096. A LDS does not have embedded control information, ...
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Relative Record Data Set
A relative record data set (RRDS) is a type of data set organization used by IBM's VSAM computer data storage system. Records are accessed based on their ordinal position in the file (''relative record number'', RRN). For example, the desired r ...
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Random access
Random access (more precisely and more generally called direct access) is the ability to access an arbitrary element of a sequence in equal time or any datum from a population of addressable elements roughly as easily and efficiently as any othe ...
References
Computer file systems
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