Glossary: Glossary

Glossary

Access Method Services: an IBM utility program that defines VSAM files, allocates space for them, modifies file attributes in the catalog, facilitates file portability between operating systems, creates backup copies of files and indexes, helps make inaccessible files accessible, and lists records and catalog entries.
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.
AMS: See Access Method Services.
base cluster: the data component of an ESDS or the data and prime index components of a KSDS.
cluster: in VSAM, a named structure consisting of a group of related components. In a KSDS, a cluster consists of a data component and an index component. In an ESDS and an RRDS, the cluster consists of a data component only.
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.
direct access: a method of access in which each record is stored and retrieved directly according to its logical address (key or relative-record number) or its address relative to the beginning of the file (relative-byte address). Data storage and retrieval depend only on the location of the data and not on a reference to data previously accessed. Direct access is synonymous with random access.
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.
fileref: a short name (or alias) for the full physical name of an external file. A SAS FILENAME statement maps the fileref to the full physical name.
index: in VSAM, a data set that relates each record's key to its relative location in the file. VSAM uses the index to sequence and locate the records of a KSDS.
key: in VSAM, one or more consecutive characters, located in the key field of each record, that are used to identify the record and establish its order with respect to the other records.
key field: in VSAM, a field that contains the record's key, which is located in the same position in each record of a KSDS.
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.
Key-Sequenced Data Set: a VSAM file type in which record order is determined by the EBCDIC collating sequence of the key field contents.
KSDS: See Key-Sequenced Data Set.
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 folder 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.
sequential access: the retrieval and storage of data in either entry sequence for an ESDS, key sequence for a KSDS, or relative-record sequence for an RRDS.
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: a multifunction, all-purpose IBM data access method.
VSAM: See Virtual Storage 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. See also operating system data set.

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