Glossary

addressed direct access

a method of access in which each record is stored and retrieved directly by its address relative to the beginning of the file (relative-byte address), which is independent of the record's location relative to data that is previously accessed. Addressed direct access can be used to access ESDS and KSDS records.

AIX

See alternate index.

alternate index

an index that is related to a given base cluster and is organized by an alternate key (a key other than the prime key of the associated base cluster data records). Its function is to provide an alternate method for locating records. An alternate index can be built over an ESDS or a KSDS. Use AMS to build an alternate index.

base cluster

the data component of an ESDS or the data and prime index components of a KSDS.

cluster

a named structure consisting of a data component, an index component, or both.

control area

a group of control intervals that compose the unit that VSAM preformats as records are added to the data set.

control interval

a contiguous area of secondary (disk) storage that VSAM uses for storing records and the control information that describes them. It is the unit of information that VSAM transmits to and from direct access storage.

DATA step view

a type of SAS data set that consists of a stored DATA step program. A DATA step view contains a definition of data that is stored elsewhere; the view does not contain the physical data. The view's input data can come from one or more sources, including external files and other SAS data sets. Because a DATA step view only reads (opens for input) other files, you cannot update the view's underlying data.

Entry-Sequenced Data Set

a VSAM file type whose record sequence is determined by the order in which the records are entered into the file, without respect to the record contents.

ESDS

See Entry-Sequenced Data Set.

key

a value that uniquely identifies a specific record and its order among other records in a database.

key field

See sequence field.

keyed direct access

a method of access in which records are retrieved and stored by specifying the record's key for a KSDS or the relative-record number (RRN) for an RRDS.

logical record

data that is requested of or given to the data management function (VSAM in this case) as a unit.

path

the route through a hierarchical file system that leads to a particular file or directory.

physical record

a unit of information that is stored on secondary (disk) storage. A physical record might consist of all or part of a logical record, and it might contain multiple logical records. Its form depends on the characteristics of the file and the disk type.

prime key

in VSAM, the main key of a key-sequenced base cluster. It is the key by which the KSDS records are initially entered and ordered. Each KSDS record must have a unique prime key.

RBA

See related-byte address.

related-byte address

the displacement of a record or control interval from the beginning of the file.

Relative-Record Data Set

a VSAM file type whose records are loaded into fixed-length slots and referenced by the record numbers of the slots.

relative-record number

in VSAM in an RRDS, a number that identifies the slot, or data space, and the record contained therein.

RRDS

See Relative-Record Data Set.

RRN

See relative-record number.

sequence field

a field that identifies and provides access to segments in a database. It contains the record's key, which is located in the same position in each record of a key-sequenced data set.

skip sequential access

a two-step process that combines both direct and sequential access. The initial record is located by keyed direct access, and subsequent records are retrieved sequentially. Skip sequential access can be used with a KSDS, an RRDS, and an ESDS that is accessed through an alternate index.

spanned record

in VSAM, a logical record that is contained in more than one control interval.

stored record

a VSAM data record, together with its control information, that is stored in auxiliary storage.

Virtual Storage Access Method

See VSAM.

VSAM

a multifunction, all-purpose IBM data access method.

VSAM catalog

a KSDS with an index that contains extensive file and volume information that VSAM requires to locate files, allocate and deallocate storage space, verify the authorization of a program or operator to gain access to a file, and accumulate file usage statistics.

VSAM data set

a classification that indicates how the records in an operating system data set are organized. VSAM is an acronym for Virtual Storage Access Method and is an IBM data access method that provides three ways to organize records in a disk file: Entry-Sequenced Data Set (ESDS), Key- Sequenced Data Set (KSDS), and Relative Record Data Set (RRDS). VSAM allows three types of access to records in VSAM files: sequential, direct, and skip sequential.

VSAM file

See VSAM data set.